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  • Pulse of dissolved organic matter alters reciprocal carbon subsidies between autotrophs and bacteria in stream food webs
    Ecol. Monogr. (IF 7.698) Pub Date : 2020-01-08
    Benoît O. L. Demars; Nikolai Friberg; Barry Thornton

    Soils are currently leaching out dissolved organic matter (DOM) at an increasing pace due to climate and land use change or recovery from acidification. The implications for stream biogeochemistry and food webs remain largely unknown, notably the metabolic balance (biotic CO2 emissions) and carbon cycling between autotrophs and bacteria. We increased by 12% the flux of DOM in a stream for three weeks to mimic a pulse of natural DOM supply from soils rich in organic matter. We were able to track its fate into the food web through the use of a before and after control impact experimental design and the addition of DOM with a distinctive δ13C signature. We used whole‐stream metabolism to quantify carbon fluxes. Both photosynthesis and heterotrophic respiration increased rapidly following C addition, but this was short lived, likely due to nutrient limitations. Carbon exchange between autotrophs and bacteria in the control stream accounted for about 49% of bacterial production and 37% of net primary production, under stable flow conditions. Net primary production relied partly (19% in the control) on natural allochthonous dissolved organic carbon via the CO2 produced by bacterial respiration, intermingling the green and brown webs. The preferential uptake of labile carbon by bacteria and excess bacterial CO2 relative to nutrients (N, P) for autotrophs shifted the reciprocal carbon exchange between bacteria and autotrophs to a predominantly one‐way carbon flow from bacteria to autotrophs, increasing the C:N:P molar ratios of autotrophs, the latter likely to become less palatable to consumers. The bacterial response to sucrose addition shifted the metabolic balance toward heterotrophy increasing biotic CO2 emissions (+125%), shortened the average distance travelled by a molecule of organic matter (−40%), and thus provided less organic matter of lower quality for downstream ecosystems. Even a small increase in labile dissolved organic matter supply due to climate and land use change could significantly alter in‐stream carbon cycling, with large effects on stream food web and biogeochemistry in small streams draining catchments with soils rich in organic carbon.

    更新日期:2020-01-08
  • Urban soil carbon and nitrogen converge at a continental scale
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-12-30
    T.L.E. Trammell; D.E. Pataki; R.V. Pouyat; Peter M. Groffman; Carl Rosier; Neil Bettez; Jeannine Cavender‐Bares; Morgan Grove; Sharon Hall; James Heffernan; Sarah E. Hobbie; Jennifer L. Morse; Christopher Neill; Meredith Steele

    In urban areas, anthropogenic drivers of ecosystem structure and function are thought to predominate over larger‐scale biophysical drivers. Residential yards are influenced by individual homeowner preferences and actions, and these factors are hypothesized to converge yard structure across broad scales. We examined soil total C and total δ13C, organic C and organic δ13C, total N, and δ15N in residential yards and corresponding reference ecosystems in six cities across the U.S. that span major climates and ecological biomes (Baltimore, MD; Boston, MA; Los Angeles, CA; Miami, FL; Minneapolis‐St. Paul, MN; and Phoenix, AZ). Across the cities, we found soil C and N concentrations and soil δ15N were less variable in residential yards compared to reference sites supporting the hypothesis that soil C, N, and δ15N converge across these cities. Increases in organic soil C, soil N, and soil δ15N across urban, suburban, and rural residential yards in several cities supported the hypothesis that soils responded similarly to altered resource inputs across cities, contributing to convergence of soil C and N in yards compared to natural systems. Soil C and N dynamics in residential yards showed evidence of increasing C and N inputs to urban soils or dampened decomposition rates over time that are influenced by climate and/or housing age across the cities. In the warmest cities (LA, Miami, Phoenix), greater organic soil C and higher soil δ13C in yards compared to reference sites reflected the greater proportion of C4 plants in these yards. In the two warm arid cities (LA, Phoenix), total soil δ13C increased and organic soil δ13C decreased with increasing home age indicating greater inorganic C in the yards around newer homes. In general, soil organic C and δ13C, soil N, and soil δ15N increased with increasing home age suggesting increased soil C and N cycling rates and associated 12C and 14N losses over time control yard soil C and N dynamics. This study provides evidence that conversion of native reference ecosystems to residential areas results in convergence of soil C and N at a continental scale. The mechanisms underlying these effects are complex and vary spatially and temporally.

    更新日期:2019-12-31
  • Food quantity–quality interactions and their impact on consumer behavior and trophic transfer
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-12-27
    Alfred Burian; Jens M. Nielsen; Monika Winder

    Food quantity–quality interactions determine growth rates and reproductive success of consumers and thereby regulate community dynamics and food web structure. Predator–prey models that shape our conceptual understanding of foraging ecology typically rely on the parametrization of fixed consumer responses to either food quantity or food quality. In nature, however, consumers optimize their fitness by responding simultaneously to changes in food quantity and quality. Therefore, we assessed consumer responses to changing food environments using a new fitness optimization model that accounted for food quality–quantity interactions to better capture the regulatory flexibility of consumers. Our simulations demonstrated that the impact of food quality on important consumer traits can be altered or even reversed by changes in food quality. Low food quality, for example, affected feeding rates negatively at low food concentrations but triggered surplus feeding at high food concentrations. The scope of surplus feeding was thereby mainly dependent on dynamics of nutrient digestion and in contrast to previous assumptions, energy costs of feeding played a minor role. Further, the regulation of digestive enzyme production, a crucial factor determining assimilation efficiencies, was strongly dependent on whether nonessential or essential nutrients were limiting growth. Consequently, not only the degree but also the type of nutrient limitation mediated the impact of the food environment on consumers’ fitness. At the community level, food quality was key in shaping predator–prey biomass ratios. High food qualities resulted in top‐heavy systems with larger consumer than prey biomass. Decreases of prey digestibility or the availability of essential nutrients, however, triggered a switch from inverted to classical pyramid shapes of bi‐trophic systems. The impact of food quantity on trophic transfer and emerging structural ecosystem properties thus critically hinges on behavioral and physiological responses of consumers. The inclusion of the regulatory flexibility of consumers is therefore an essential next step to improve predator–prey models and our conceptual understanding of trophic interactions.

    更新日期:2019-12-29
  • Overfishing and the ecological impacts of extirpating large parrotfish from Caribbean coral reefs
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-12-22
    Andrew A. Shantz; Mark C. Ladd; Deron E. Burkepile

    The unique traits of large animals often allow them to fulfill functional roles in ecosystems that small animals cannot. However, large animals are also at greater risk from human activities. Thus, it is critical to understand how losing large animals impacts ecosystem function. In the oceans, selective fishing for large animals alters the demographics and size‐structure of numerous species. While the community‐wide impacts of losing large animals is a major theme in terrestrial research, the ecological consequences of removing large animals from marine ecosystems remain understudied. Here, we combine survey data from 282 sites across the Caribbean with a field experiment to investigate how altering the size‐structure of parrotfish populations impacts coral reef communities. We show that Caribbean‐wide, parrotfish populations are skewed towards smaller individuals, with fishes < 11 cm in length comprising nearly 70% of the population in the most heavily fished locations versus ~ 25% at minimally fished sites. Despite these differences in size‐structure, sites had similar overall parrotfish biomass. As a result, algal cover was unrelated to parrotfish biomass and instead, was negatively correlated with the density of large parrotfishes. To mechanistically explore how large parrotfishes shape benthic communities, we manipulated fishes’ access to the benthos to create three distinct fish communities with different size‐structure. We found that excluding large or large and medium‐sized parrotfishes did not alter overall parrotfish grazing rates but caused respective 4‐ and 10‐fold increases in algal biomass. Unexpectedly, branching corals benefited from excluding large parrotfishes whereas the growth of mounding coral species was impaired. Similarly, removing large parrotfishes led to unexpected increases in coral recruitment that were absent when both large and medium bodied fishes were excluded. Our data highlight the unique roles of large parrotfishes in driving benthic dynamics on coral reefs and suggests that diversity of size is an important component of how herbivore diversity impacts ecosystem function on reefs. This study adds to a growing body of literature revealing the ecological ramifications of removing large animals from ecosystems and sheds new light on how fishing down the size‐structure of parrotfish populations alters functional diversity to reshape benthic reef communities.

    更新日期:2019-12-23
  • Flower traits, habitat, and phylogeny as predictors of pollinator service: a plant community perspective
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-12-21
    Carlos M. Herrera

    Pollinator service is essential for successful sexual reproduction and long‐term population persistence of animal‐pollinated plants, and innumerable studies have shown that insufficient service by pollinators results in impaired sexual reproduction (“pollen limitation”). Studies directly addressing the predictors of variation in pollinator service across species or habitats remain comparatively scarce, which limits our understanding of the primary causes of natural variation in pollen limitation. This paper evaluates the importance of pollination‐related features, evolutionary history and environment as predictors of pollinator service in a large sample of plant species from undisturbed montane habitats in southeastern Spain. Quantitative data on pollinator visitation were obtained for 191 insect‐pollinated species belonging to 142 genera in 43 families, and the predictive values of simple floral traits (perianth type, class of pollinator visitation unit, and visitation unit dry mass), phylogeny, and habitat type were assessed. A total of 24,866 pollinator censuses accounting for 5,414,856 flower‐min of observation were conducted on 510 different dates. Flowering patch and single flower visitation probabilities by all pollinators combined were significantly predicted by the combined effects of perianth type (open vs. restricted), class of visitation unit (single flower vs. flower packet), mass of visitation unit, phylogenetic relationships, and habitat type. Pollinator composition at insect order level varied extensively among plant species, largely reflecting the contrasting visitation responses of Coleoptera, Diptera, Hymenoptera and Lepidoptera to variation in floral traits. Pollinator composition had a strong phylogenetic component, and the distribution of phylogenetic autocorrelation hotspots of visitation rates across the plant phylogeny differed widely among insect orders. Habitat type was a key predictor of pollinator composition, as major insect orders exhibited decoupled variation across habitat types in visitation rates. Comprehensive pollinator sampling of a regional plant community has shown that pollinator visitation and composition can be parsimoniously predicted by a combination of simple floral features, habitat type and evolutionary history. Ambitious community‐level studies can help to formulate novel hypotheses and questions, shed fresh light on long‐standing controversies in pollination research (e.g., “pollination syndromes”), and identify methodological cautions that should be considered in pollination community studies dealing with small, phylogenetically‐biased plant species samples.

    更新日期:2019-12-21
  • Reviewing the role of plant litter inputs to forested wetland ecosystems: leafing through the literature
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-12-12
    Aaron B. Stoler; Rick A. Relyea

    The input of senescent terrestrial leaf litter into soil and aquatic ecosystems is one of the most massive cyclic subsidies on Earth, particularly within forested ecosystems. For freshwater systems embedded within forests, litter inputs provide a vital source of energy and nutrients that allows greater production than in‐situ resources can provide. In return, freshwater food webs can provide an enormous amount of material to the terrestrial landscape through biotic respiration, photosynthesis, and organism emergence. Most research concerning this important aquatic‐terrestrial link has focused on lotic ecosystems (i.e., streams and rivers); far less attention has been given to its role in lentic systems (i.e., wetlands and lakes). A focus on small forested wetlands is particularly important, as these systems account for a disproportionate amount of global carbon flux relative to their spatial coverage, and the decomposition of leaf litter is a major contributor. Here, we review six themes: 1) the evidence for the role of leaf litter inputs as an ecologically important subsidy in forested wetlands; 2) the bottom‐up effects of quantitative and qualitative variation in litter inputs; 3) how diversity in litter mixtures can alter ecological functioning; 4) evidence for top‐down consequences of litter inputs through toxic effects on predators and parasites, and the alteration of predator‐prey interactions; 5) the relevance of our review to other research fields by considering the role of litter inputs relative to other types of subsidies and environmental gradients (e.g., temperature, canopy cover, and hydrology); and 6) the interaction of litter subsidies with anthropogenic disturbances. We conclude by highlighting several high‐priority research questions and providing suggestions for future research on the role of litter subsidies in freshwater ecosystems.

    更新日期:2019-12-13
  • Removal of grazers alters the response of tundra soil carbon to warming and enhanced nitrogen availability
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-12-09
    Henni Ylänne, Elina Kaarlejärvi, Maria Väisänen, Minna K. Männistö, Saija H. K. Ahonen, Johan Olofsson, Sari Stark

    The circumpolar Arctic is currently facing multiple global changes that have the potential to alter the capacity of tundra soils to store carbon. Yet, predicting changes in soil carbon is hindered by the fact that multiple factors simultaneously control processes sustaining carbon storage and we do not understand how they act in concert. Here, we investigated the effects of warmer temperatures, enhanced soil nitrogen availability, and the combination of these on tundra carbon stocks at three different grazing regimes: on areas with over 50‐yr history of either light or heavy reindeer grazing and in 5‐yr‐old exlosures in the heavily grazed area. In line with earlier reports, warming generally decreased soil carbon stocks. However, our results suggest that the mechanisms by which warming decreases carbon storage depend on grazing intensity: under long‐term light grazing soil carbon losses were linked to higher shrub abundance and higher enzymatic activities, whereas under long‐term heavy grazing, carbon losses were linked to drier soils and higher enzymatic activities. Importantly, under enhanced soil nitrogen availability, warming did not induce soil carbon losses under either of the long‐term grazing regimes, whereas inside exclosures in the heavily grazed area, also the combination of warming and enhanced nutrient availability induced soil carbon loss. Grazing on its own did not influence the soil carbon stocks. These results reveal that accounting for the effect of warming or grazing alone is not sufficient to reliably predict future soil carbon storage in the tundra. Instead, the joint effects of multiple global changes need to be accounted for, with a special focus given to abrupt changes in grazing currently taking place in several parts of the Arctic.

    更新日期:2019-12-09
  • Spatiotemporal patterns of microbial composition and diversity in precipitation
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-12-02
    Ken A. Aho, Carolyn F. Weber, Brent C. Christner, Boris A. Vinatzer, Cindy E. Morris, Rachel Joyce, Kevin C. Failor, Jason T. Werth, Aurora L. H. Bayless‐Edwards, David G. Schmale

    Microbes in the atmosphere have broad ecological impacts, including the potential to trigger precipitation through species and strains that act as ice nucleation particles. To characterize spatiotemporal trends of microbial assemblages in precipitation we sequenced 16S (bacterial) and 18S (fungal) rRNA gene amplicon libraries collected from 72 precipitation events in three U.S. states (Idaho, Louisiana, and Virginia) over four seasons. We considered these data from the perspective of a novel metacommunity framework. In agreement with our heuristic, we found evidence for distinct mechanisms underlying the composition and diversity of bacterial and fungal assemblages in precipitation. Specifically, we determined that (1) bacterial operational taxonomic unit (OTU) composition of precipitation was strongly associated with macroscale drivers including season and high‐altitude characteristics of storms; (2) fungal OTU composition was strongly correlated with mesoscale drivers including particular spatial locations; (3) β‐diversity (heterogeneity of taxa among samples) for both bacteria and fungi was largely maintained by turnover of taxa; however, (4) bacterial assemblages had higher contributions to total β‐diversity from nestedness (i.e., lower richness assemblages were largely taxonomic subsets of richer assemblages), due to losses of taxa during dispersal, particularly among potential ice nucleation active bacteria; and (5) fungal assemblages had higher contributions to total β‐diversity from turnover due to OTU replacement. Spatiotemporal trends in precipitation‐borne metacommunities allowed delineation of a large number of statistically significant indicator taxa for particular sites and seasons, including trends for bacteria that are potentially ice nucleation active. Our findings advance understanding regarding the dispersion of aerosolized microbes via wet deposition, and the development of theory concerning potential assembly rules for bioaerosol assemblages.

    更新日期:2019-12-03
  • Clinal variation in drought resistance shapes past population declines and future management of a threatened plant
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-11-29
    Paul D. Krushelnycky, Jesse M. Felts, Robert H. Robichaux, Kasey E. Barton, Creighton M. Litton, Matthew D. Brown

    Predicting vegetation responses to increased future drought is challenging, owing to the complex interaction of multiple factors influencing both plant drought resistance and local climatic conditions, each of which may be subject to spatial and temporal heterogeneity. We conducted a detailed study of potential mechanisms underlying an elevational gradient in mortality that has characterized recent population declines of a threatened alpine plant, the Haleakalā silversword (Argyroxiphium sandwicense subsp. macrocephalum). We used a pair of greenhouse experiments staged at high and low elevations to test the influences of plasticity (to contrasting soil water availability and atmospheric conditions) and heredity (different seed source elevations) on the development of functional traits associated with drought resistance and on performance in a terminal drought. We then out‐planted a subset of plants into three common‐garden plots near the bottom, middle and top of the silversword elevational range, and tracked growth and survival over 3.5 years. A range of morphological traits (root and leaf mass fractions, specific leaf area, leaf area ratio, and root length per shoot mass) exhibited either heritable variation or plasticity, or both. Among physiological traits measured, only water use efficiency exhibited a plastic treatment response. Survival of out‐plants was influenced during the first year by a home site advantage, and by the water treatment imposed in the greenhouses, with high water plants dying more often than low water plants. These effects subsequently dissipated, being replaced over the final 1.5 years by a strengthening out‐plant site effect: survival was positively associated with site elevation, matching the pattern of mortality observed in the wild population. The balance of information suggests this pattern stems from lower elevation plants being less drought resistant than higher elevation plants, owing principally to plasticity, and thus suffering greater mortality during recent dry seasons. The pattern may be enhanced by stronger deviations from typical climatic conditions at lower elevations. Our findings suggest that future management should focus on climatically suitable habitat rather than advantageous genetic ecotypes. More broadly, they provide evidence that clinal variation can be important to consider when modelling future vegetation responses to climate change.

    更新日期:2019-11-30
  • The impact of yeast presence in nectar on bumble bee behavior and fitness
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-11-19
    María I. Pozo, Gaby van Kemenade, Annette van Oystaeyen, Tomás Aledón‐Catalá, Alfredo Benavente, Wim Van den Ende, Felix Wäckers, Hans Jacquemyn

    The presence of yeasts in pollen and floral nectar is rather the norm than the exception. Due to the metabolic activities of yeasts, sugar and amino acid composition of nectar often drastically change and may negatively impact the nutritional value of nectar for pollinators and hence insect fitness. On the other hand, the presence of yeasts in floral nectar may also increase its nutritional value due to yeast's probiotic effect and the release of yeast's metabolites. In this study, we investigated whether the presence of defined flower‐ and insect‐associated yeasts affected individual and colony fitness of the bumble bee pollinator Bombus terrestris. Specifically, we tested whether the presence of yeasts in nectar affected bumble bee foraging behavior and nectar consumption, individual growth and colony development, larval and queen mortality, and mating success. Quantitative analyses of sugar and amino acid profiles showed that nectar yeasts significantly affected the chemical composition of nectar. However, dual‐choice experiments indicated that yeast inoculation did not significantly affect foraging behavior or consumption rates. Nest development, on the other hand, was significantly affected by the presence of yeasts, but effects largely depended on species identity, with Candida bombiphila, Metschnikowia gruessii, and Rhodotorula mucilaginosa having the largest positive impact on colony growth. Interestingly, the effects at the colony level were more pronounced than at the individual level. In vitro growth tests further showed that yeasts have the potential to suppress the growth of the bumble bee gut pathogen Crithidia bombi. Overall, these results demonstrate that nectar‐inhabiting yeasts can have diverse effects on bumble bee fitness and therefore may mediate plant–pollinator mutualisms.

    更新日期:2019-11-20
  • Multiple metrics of latitudinal patterns in insect pollination and herbivory for a tropical‐temperate congener pair
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-11-12
    Carina A. Baskett, Lucy Schroeder, Marjorie G. Weber, Douglas W. Schemske

    The biotic interactions hypothesis posits that biotic interactions are more important drivers of adaptation closer to the equator, evidenced by “stronger” contemporary interactions (e.g. greater interaction rates) and/or patterns of trait evolution consistent with a history of stronger interactions. Support for the hypothesis is mixed, but few studies span tropical and temperate regions while experimentally controlling for evolutionary history. Here, we integrate field observations and common garden experiments to quantify the relative importance of pollination and herbivory in a pair of tropical‐temperate congeneric perennial herbs. Phytolacca rivinoides and P. americana are pioneer species native to the Neotropics and the eastern USA, respectively. We compared plant‐pollinator and plant‐herbivore interactions between three tropical populations of P. rivinoides from Costa Rica and three temperate populations of P. americana from its northern range edge in Michigan and Ohio. For some metrics of interaction importance, we also included three subtropical populations of P. americana from its southern range edge in Florida. This approach confounds species and region but allows us, uniquely, to measure complementary proxies of interaction importance across a tropical‐temperate range in one system. To test the prediction that lower‐latitude plants are more reliant on insect pollinators, we quantified floral display and reward, insect visitation rates, and self‐pollination ability (autogamy). To test the prediction that lower‐latitude plants experience more herbivore pressure, we quantified herbivory rates, herbivore abundance, and leaf palatability. We found evidence supporting the biotic interactions hypothesis for most comparisons between P. rivinoides and north‐temperate P. americana (floral display, insect visitation, autogamy, herbivory, herbivore abundance, and young‐leaf palatability). Results for subtropical P. americana populations, however, were typically not intermediate between P. rivinoides and north‐temperate P. americana, as would be predicted by a linear latitudinal gradient in interaction importance. Subtropical young‐leaf palatability was intermediate, but subtropical mature leaves were the least palatable, and pollination‐related traits did not differ between temperate and subtropical regions. These nonlinear patterns of interaction importance suggest future work to relate interaction importance to climatic or biotic thresholds. In sum, we found that the biotic interactions hypothesis was more consistently supported at the larger spatial scale of our study.

    更新日期:2019-11-13
  • Obtaining birth and mortality patterns from structured population trajectories.
    Ecol. Monogr. (IF 7.698) Pub Date : 1994-02-01
    S N Wood

    "A method is presented for unravelling the demographic equation for structured populations. A solution to the McKendrick-von Foerster equation is constructed using spline functions and this is fitted to stage-structured population data in such a way that the solution is smooth, positive, and does not imply negative death rates. The smoothness of the surface, and hence the complexity of the population model, is determined in a statistically optimum manner using cross validation. Time- and age-dependent death rates can be obtained as well as time-dependent birth rates. Confidence intervals are obtained for population size and death rates that give a 95% probability that the true population dynamics are within the intervals. Practical application of the method is demonstrated, and comparison made with three alternative methods."

    更新日期:2019-11-01
  • From early life to senescence: individual heterogeneity in a long-lived seabird.
    Ecol. Monogr. (IF 7.698) Pub Date : 2018-08-21
    Rémi Fay,Christophe Barbraud,Karine Delord,Henri Weimerskirch

    Although population studies have long assumed that all individuals of a given sex and age are identical, ignoring among-individual differences may strongly bias our perception of eco-evolutionary processes. Individual heterogeneity, often referred to as individual quality, has received increasing research attention in the last decades. However, there are still substantial gaps in our current knowledge. For example, there is little information on how individual heterogeneity influences various life-history traits simultaneously, and studies describing individual heterogeneity in wild populations are generally not able to jointly identify possible sources of this variation. Here, based on a mark-recapture data set of 9,685 known-aged Wandering Albatrosses (Diomedea exulans), we investigated the existence of individual quality over the entire life cycle of this species, from early life to senescence. Using finite mixture models, we investigated the expression of individual heterogeneity in various demographic traits, and examined the origin of these among-individual differences by considering the natal environmental conditions. We found that some individuals consistently outperformed others during most of their life. In old age, however, the senescence rate was stronger in males that showed high demographic performance at younger ages. Variation in individual quality seemed strongly affected by extrinsic factors experienced during the ontogenetic period. We found that individuals born in years with high population density tended to have lower performances during their lifespan, suggesting delayed density dependence effects through individual quality. Our study showed that among-individual differences could be important in structuring individual life history trajectories, with substantial consequences at higher ecological levels such as population dynamics.

    更新日期:2019-11-01
  • The impact of future forest dynamics on climate: interactive effects of changing vegetation and disturbance regimes.
    Ecol. Monogr. (IF 7.698) Pub Date : 2018-04-10
    Dominik Thom,Werner Rammer,Rupert Seidl

    Currently, the temperate forest biome cools the earth's climate and dampens anthropogenic climate change. However, climate change will substantially alter forest dynamics in the future, affecting the climate regulation function of forests. Increasing natural disturbances can reduce carbon uptake and evaporative cooling, but at the same time increase the albedo of a landscape. Simultaneous changes in vegetation composition can mitigate disturbance impacts, but also influence climate regulation directly (e.g., via albedo changes). As a result of a number of interactive drivers (changes in climate, vegetation, and disturbance) and their simultaneous effects on climate-relevant processes (carbon exchange, albedo, latent heat flux) the future climate regulation function of forests remains highly uncertain. Here we address these complex interactions to assess the effect of future forest dynamics on the climate system. Our specific objectives were (1) to investigate the long-term interactions between changing vegetation composition and disturbance regimes under climate change, (2) to quantify the response of climate regulation to changes in forest dynamics, and (3) to identify the main drivers of the future influence of forests on the climate system. We investigated these issues using the individual-based forest landscape and disturbance model (iLand). Simulations were run over 200 yr for Kalkalpen National Park (Austria), assuming different future climate projections, and incorporating dynamically responding wind and bark beetle disturbances. To consistently assess the net effect on climate the simulated responses of carbon exchange, albedo, and latent heat flux were expressed as contributions to radiative forcing. We found that climate change increased disturbances (+27.7% over 200 yr) and specifically bark beetle activity during the 21st century. However, negative feedbacks from a simultaneously changing tree species composition (+28.0% broadleaved species) decreased disturbance activity in the long run (-10.1%), mainly by reducing the host trees available for bark beetles. Climate change and the resulting future forest dynamics significantly reduced the climate regulation function of the landscape, increasing radiative forcing by up to +10.2% on average over 200 yr. Overall, radiative forcing was most strongly driven by carbon exchange. We conclude that future changes in forest dynamics can cause amplifying climate feedbacks from temperate forest ecosystems.

    更新日期:2019-11-01
  • Effects of soil microbes on plant competition: a perspective from modern coexistence theory
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-10-21
    Po‐Ju Ke, Joe Wan

    Growing evidence shows that soil microbes affect plant coexistence in a variety of systems. However, since these systems vary in the impacts microbes have on plants and in the ways plants compete with each other, it is challenging to integrate results into a general predictive theory. To this end, we suggest that the concepts of niche and fitness difference from modern coexistence theory should be used to contextualize how soil microbes contribute to plant coexistence. Synthesizing a range of mechanisms under a general plant–soil microbe interaction model, we show that, depending on host specificity, both pathogens and mutualists can affect the niche difference between competing plants. However, we emphasize the need to also consider the effect of soil microbes on plant fitness differences, a role often overlooked when examining their role in plant coexistence. Additionally, since our framework predicts that soil microbes modify the importance of plant–plant competition relative to other factors for determining the outcome of competition, we suggest that experimental work should simultaneously quantify microbial effects and plant competition. Thus, we propose experimental designs that efficiently measure both processes and show how our framework can be applied to identify the underlying drivers of coexistence. Using an empirical case study, we demonstrate that the processes driving coexistence can be counterintuitive, and that our general predictive framework provides a better way to identify the true processes through which soil microbes affect coexistence.

    更新日期:2019-10-21
  • The ecology and evolution of seed predation by Darwin's finches on Tribulus cistoides on the Galápagos Islands
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-10-21
    Sofía Carvajal‐Endara, Andrew P. Hendry, Nancy C. Emery, Corey P. Neu, Diego Carmona, Kiyoko M. Gotanda, T. Jonathan Davies, Jaime A. Chaves, Marc T. J. Johnson

    Predator–prey interactions play a key role in the evolution of species traits through antagonistic coevolutionary arms races. The evolution of beak morphology in the Darwin's finches in response to competition for seed resources is a classic example of evolution by natural selection. The seeds of Tribulus cistoides are an important food source for the largest ground finch species (Geospiza fortis, G. magnirostris, and G. conirostris) in dry months, and the hard spiny morphology of the fruits is a potent agent of selection that drives contemporary evolutionary change in finch beak morphology. Although the effects of these interactions on finches are well known, how seed predation affects the ecology and evolution of the plants is poorly understood. Here we examine whether seed predation by Darwin's finches affects the ecology and evolution of T. cistoides. We ask whether the intensity of seed predation and the strength of natural selection by finches on fruit defense traits vary among populations, islands, years, or with varying finch community composition (i.e., the presence/absence of the largest beaked species, which feed on T. cistoides most easily). We then further test whether T. cistoides fruit defenses have diverged among islands in response to spatial variation in finch communities. We addressed these questions by examining seed predation by finches in 30 populations of T. cistoides over 3 yr. Our study reveals three key results. First, Darwin's finches strongly influence T. cistoides seed survival, whereby seed predation varies with differences in finch community composition among islands and in response to interannual fluctuations in precipitation. Second, finches impose phenotypic selection on T. cistoides fruit morphology, whereby smaller and harder fruits with longer or more spines exhibited higher seed survival. Variation in finch community composition and precipitation also explains variation in phenotypic selection on fruit defense traits. Third, variation in the number of spines on fruits among islands is consistent with divergent phenotypic selection imposed by variation in finch community composition among islands. These results suggest that Darwin's finches and T. cistoides are experiencing an ongoing coevolutionary arms race, and that the strength of this coevolution varies in space and time.

    更新日期:2019-10-21
  • Persistence and turnover in desert plant communities during a 37‐yr period of land use and climate change
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-08-26
    Scott R. Abella, Ross J. Guida, Chris L. Roberts, Carrie M. Norman, James S. Holland

    Understanding long‐term changes in ecological communities during global change is a priority for 21st‐century ecology. Deserts, already at climatic extremes, are of unique interest because they are projected to be ecosystems most responsive to global change. Within a 500‐km2 landscape in the Mojave Desert, USA, we measured perennial plant communities at 100 sites three times (1979, 2008, and 2016) during 37 yr to evaluate six hypotheses of community change. These hypotheses encompassed shifts in community measures (e.g., diversity, cover) and species elevational distributions, biotic homogenization, disproportionately large change at the highest elevations, relationships between turnover and species’ responses to disturbance and drought, and that environmental refugia (e.g., moist topographic positions) would receive species during climatic warming and drying. Most community measures changed temporally, such as species density (species/600 m2) increasing 23% and plant cover doubling between 1979 and 2016. There was no increase in nonnative species and minimal evidence for biotic homogenization. High‐elevation communities did not display greater change than low‐elevation communities. Moreover, environmental refugia factored little in species shifts. While species distributional changes were unrelated to affinity for disturbance, the six most persistent species (persisting on >80% of sites) were long‐lived shrubs not associated with disturbance. Overall, seemingly paradoxically, climatic warming and drying was associated with increasing plant abundance. Comparing the 1970s to 2007–2016, precipitation in the study area declined 16% from 17 to 14 cm/yr and average daily minimum temperature rose 13% (1.2°C). The current climate with fewer freezes, together with reduced grazing, could be among the most optimal for desert perennials in the past century, although potential response lags to continuing warming and drying are uncertain. This study of long‐term elevational shifts in communities during global change is among few in deserts, and the average upward elevational shift of 6 m/decade for species in our study is within the range reported for temperate biomes. However, the 41% of species moving downslope is unusually high. We propose that dynamics within desert perennial communities follow a core‐transient species model where a site's species are either highly persistent or transient in approximately equal proportions.

    更新日期:2019-08-26
  • Disentangling herbivore impacts in primary succession by refocusing the plant stress and vigor hypotheses on phenology
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-08-23
    Christian Che‐Castaldo, Charlie M. Crisafulli, John G. Bishop, Elise F. Zipkin, William F. Fagan

    The plant stress and plant vigor hypotheses are widely used to explain the distribution and abundance of insect herbivores across their host plants. These hypotheses are the subject of contentious debate within the plant herbivore research community, with several studies finding simultaneous support for both hypotheses for the same plant–herbivore interaction. We address the question of how such support is possible using dynamic site‐occupancy models to quantify the attack dynamics of Cryptorhynchus lapathi (poplar‐willow weevil) on Salix sitchensis (Sitka willow), a dioecious shrub colonizing Mount St. Helens, Washington, USA after the 1980 eruption, in relation to host plant stress, vigor, and sex. We also introduce several scaling criteria as a rigorous test of the plant vigor hypothesis and demonstrate why modeling insect detection is important in plant–insect studies. Weevils responded positively to water stress associated with seasonal dry‐downs, and this response was phenologically compartmentalized by larval feeding mode. Weevils preferentially attacked large and/or flowering stems, imposing an ecological cost on willow reproduction via increased stem mortality and susceptibility to future attack. We propose that the dual response to host plant stress and vigor is due to the synchronization between young weevil larval feeding and willow nutrient pulses that are mediated by environmental stress. In turn, this process drives successional dynamics, causing the juvenilization of upland willow plants and possibly delaying establishment of a willow‐dominated upland sere. These results highlight the common, but often overlooked, phenological basis of the plant stress and plant vigor hypotheses, which both focus on how stress changes the quality of plant resources available to immature insects.

    更新日期:2019-08-25
  • Demographic and population responses of an apex predator to climate and its prey: a long‐term study of South Polar Skuas
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-08-13
    Nathan Pacoureau, Karine Delord, Stéphanie Jenouvrier, Christophe Barbraud

    Ecologists widely acknowledge that a complex interplay of endogenous (density‐dependent) and exogenous (density‐independent) factors impact demographic processes. Individuals respond differently to those forces, ultimately shaping the dynamics of wild populations. Most comprehensive studies disentangling simultaneously the effects of density dependence, climate, and prey abundance while taking into account age structure were conducted in terrestrial ecosystems. However, studies on marine populations are lacking. Here we provide insight into the mechanisms affecting four vital rates of an apex Antarctic marine predator population, the South Polar Skua Catharacta maccormicki, by combining a nearly half‐century longitudinal time series of individual life histories and abundance data, with climatic and prey abundance covariates. Using multistate capture–mark–recapture models, we estimated age classes effects on survival, breeding, successful breeding with one or two chicks and successful breeding with two chicks probabilities, and assessed the different effects of population size, climate, and prey abundance on each age‐specific demographic parameter. We found evidence for strong age effects in the four vital rates studied. Vital rates at younger ages were lower than those of older age classes for all parameters. Results clearly evidenced direct and indirect influences of local climate (summer sea ice concentration), of available prey resources (penguins), and of intrinsic factors (size of the breeding population). More covariate effects were found on reproductive rates than on survival, and younger age classes were more sensitive than the older ones. Results from a deterministic age‐structured density‐dependent matrix population model indicated greater effects of prey abundance and sea ice concentration on the total population size than on the breeding population size. Both total population size and the number of breeders were strongly affected by low values of sea ice concentration. Overall, our results highlight the greater sensitivity of reproductive traits and of younger age classes to prey abundance, climate variability, and density dependence in a marine apex predator, with important consequences on the total population size but with limited effects on the breeding population size. We discuss the mechanisms by which climate variability, prey abundance, and population size may affect differentially age‐specific vital rates, and the potential population consequences of future environmental changes.

    更新日期:2019-08-14
  • Geographic variation in the intensity of warming and phenological mismatch between Arctic shorebirds and invertebrates
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-07-24
    Eunbi Kwon, Emily L. Weiser, Richard B. Lanctot, Stephen C. Brown, Heather R. Gates, Grant Gilchrist, Steve J. Kendall, David B. Lank, Joseph R. Liebezeit, Laura McKinnon, Erica Nol, David C. Payer, Jennie Rausch, Daniel J. Rinella, Sarah T. Saalfeld, Nathan R. Senner, Paul A. Smith, David Ward, Robert W. Wisseman, Brett K. Sandercock

    Responses to climate change can vary across functional groups and trophic levels, leading to a temporal decoupling of trophic interactions or “phenological mismatches.” Despite a growing number of single‐species studies that identified phenological mismatches as a nearly universal consequence of climate change, we have a limited understanding of the spatial variation in the intensity of this phenomenon and what influences this variation. In this study, we tested for geographic patterns in phenological mismatches between six species of shorebirds and their invertebrate prey at 10 sites spread across ~13° latitude and ~84° longitude in the Arctic over three years. At each site, we quantified the phenological mismatch between shorebirds and their invertebrate prey at (1) an individual‐nest level, as the difference in days between the seasonal peak in food and the peak demand by chicks, and (2) a population level, as the overlapped area under fitted curves for total daily biomass of invertebrates and dates of the peak demand by chicks. We tested whether the intensity of past climatic change observed at each site corresponded with the extent of phenological mismatch and used structural equation modeling to test for causal relationships among (1) environmental factors, including geographic location and current climatic conditions, (2) the timing of invertebrate emergence and the breeding phenology of shorebirds, and (3) the phenological mismatch between the two trophic levels. The extent of phenological mismatch varied more among different sites than among different species within each site. A greater extent of phenological mismatch at both the individual‐nest and population levels coincided with changes in the timing of snowmelt as well as the potential dissociation of long‐term snow phenology from changes in temperature. The timing of snowmelt also affected the shape of the food and demand curves, which determined the extent of phenological mismatch at the population level. Finally, we found larger mismatches at more easterly longitudes, which may be affecting the population dynamics of shorebirds, as two of our study species show regional population declines in only the eastern part of their range. This suggests that phenological mismatches may be resulting in demographic consequences for Arctic‐nesting birds.

    更新日期:2019-07-25
  • Climate outweighs native vs. nonnative range‐effects for genetics and common garden performance of a cosmopolitan weed
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-07-22
    Christoph Rosche, Isabell Hensen, Adrian Schaar, Uzma Zehra, Marie Jasieniuk, Ragan M. Callaway, Damase P. Khasa, Mohammad M. Al‐Gharaibeh, Ylva Lekberg, Dávid U. Nagy, Robert W. Pal, Miki Okada, Karin Schrieber, Kathryn G. Turner, Susanne Lachmuth, Andrey Erst, Tomonori Tsunoda, Min Sheng, Robin Schmidt, Yanling Peng, Wenbo Luo, Yun Jäschke, Zafar A. Reshi, Manzoor A. Shah

    Comparing genetic diversity, genetic differentiation, and performance between native and nonnative populations has advanced our knowledge of contemporary evolution and its ecological consequences. However, such between‐range comparisons can be complicated by high among‐population variation within native and nonnative ranges. For example, native vs. nonnative comparisons between small and non‐representative subsets of populations for species with very large distributions have the potential to mislead because they may not sufficiently account for within‐range adaptation to climatic conditions, and demographic history that may lead to non‐adaptive evolution. We used the cosmopolitan weed Conyza canadensis to study the interplay of adaptive and demographic processes across, to our knowledge, the broadest climatic gradient yet investigated in this context. To examine the distribution of genetic diversity, we genotyped 26 native and 26 nonnative populations at 12 microsatellite loci. Furthermore, we recorded performance traits for 12 native and 13 nonnative populations in the field and in the common garden. To analyze how performance was related to range and/or climate, we fit pedigree mixed‐effects models. These models weighed the population random effect for co‐ancestry to account for the influence of demographic history on phenotypic among‐population differentiation. Genetic diversity was very low, selfing rates were very high, and both were comparable between native and nonnative ranges. Nonnative populations out‐performed native populations in the field. However, our most salient result was that both neutral genetic differentiation and common garden performance were far more correlated with the climatic conditions from which populations originated than native vs. nonnative range affiliation. Including co‐ancestry of our populations in our models greatly increased explained variance and our ability to detect significant main effects for among‐population variation in performance. High propagule pressure and high selfing rates, in concert with the ability to adapt rapidly to climatic gradients, may have facilitated the global success of this weed. Neither native nor nonnative populations were homogeneous groups but responded comparably to similar environments in each range. We suggest that studies of contemporary evolution should consider widely distributed and genotyped populations to disentangle native vs. nonnative range effects from varying adaptive processes within ranges and from potentially confounding effects of demographic history.

    更新日期:2019-07-22
  • Foodwebs based on unreliable foundations: spatiotemporal masting merged with consumer movement, storage, and diet
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-07-17
    James S. Clark, Chase Nuñez, Bradley Tomasek

    Mast‐fruiting trees represent a pulsed resource that both supports and destabilizes consumer populations. Whereas a reliable resource is abundant on average and with limited variation in time and space, masting is volatile and localized, and that variability ramifies throughout food‐webs. Theory is developed to evaluate how the space–time structure of masting interacts with consumers who exploit alternative hosts, forage widely in space, and store reserves in time. We derive the space–time–species covariance in resource supply and combine it with the space–time–diet breadth of consumers, or ambit. Direct connection to data is made possible with Mast Inference and Forecasting (MASTIF), a state‐space autoregressive model that fits seed‐trap and canopy observations and predicts resource availability within the canopy and on the forest floor with full uncertainty. A resource score can be assigned to each consumer–habitat combination that integrates the benefits of a high mean supply weighed against the variance cost. As the consumer ambit increases, the volatility of an unreliable resource shifts from a variance cost to a mean benefit. Consumers foraging in the canopy (arboreal arthropods and rodents, song birds) experience space‐time covariance between host trees. Consumers on the forest floor (seed and damping‐off fungi, arthropods, rodents, ground‐nesting birds, mammals) experience instead a redistribution of that covariance by dispersal. For consumers lacking mobility, demographic storage in the form of episodic birth cohorts following mast years is important for population persistence. Consumers additionally compensate volatility with diet breadth. Depending on the dominant masting strategies of host tree species in the diet, habitats differentially limit consumers depending on the misalignment between consumer ambit and spatiotemporal covariance of hosts. The impact of adding or subtracting a diet item can be gauged with the standard error (SE) rule or the benefit of an added diet item balanced against the variance cost, both of which depend on the existing diet, the abundance of the new host, and the consumer's foraging ambit. Results rank habitats by their capacities to support wildlife and other consumers from a resource perspective. Results are connected directly to data, with full uncertainty, by MASTIF.

    更新日期:2019-07-18
  • How extreme is extreme? Demographic approaches inform the occurrence and ecological relevance of extreme events
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-07-16
    Christopher E. Latimer, Benjamin Zuckerberg

    Projected increases in the variability of both temperature and precipitation will result in the greater likelihood and magnitude of extreme weather (e.g., cold snaps, droughts, heat waves) with potential implications for animal populations. Despite the ecological consequences of extreme weather, there are several challenges in identifying extreme events and measuring their influence on key demographic processes in free‐living animals. First, there is often a mismatch between the spatial and/or temporal resolution of biological and climate data that could hinder our ability to draw accurate inferences about how species and populations respond to extreme events. Second, there are multiple approaches for identifying an extreme event ranging from statistical definitions (e.g., standardized deviates) to species‐specific biological thresholds. Lastly, the impacts of extreme weather on species can vary as a function of differences in exposure and intrinsic sensitivity to climate variability. In the Northern Hemisphere, rapid warming has contributed to a “wobblier” jet stream that promotes the higher likelihood of cold Arctic air moving southward and leading to more extreme winter conditions. Due to these conditions, the Upper Midwest experienced two of the coldest winters in the past 35 yr during 2014 and 2015. We combined radiofrequency identification technologies with fine‐scale weather data and standard capture–mark–recapture analyses to estimate weekly and overwinter survival rates of a common winter passerine, the Black‐capped Chickadee (Poecile atricapillus), in a near continuous fashion. Using both statistical and biological definitions of weather extremes, we found that declining ambient temperatures reduced survival (despite the presence of favorable microclimates), and that biologically defined thresholds of extreme weather were better at explaining variation in survival than statistical ones. Moreover, habitat fragmentation interacted with temperature to modify the exposure of birds to extreme weather with survival consequences, but sensitivity, as measured by body condition, did not appear to play a significant role. These results provide a novel contribution to the understanding of how extreme weather may interact with local‐ and landscape features to influence the demography of species and populations, and suggest potential opportunities for climate‐change adaptation in human‐dominated landscapes.

    更新日期:2019-07-17
  • Compound‐specific isotope analysis of amino acids as a new tool to uncover trophic chains in soil food webs
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-07-09
    Melanie M. Pollierer, Thomas Larsen, Anton Potapov, Adrian Brückner, Michael Heethoff, Jens Dyckmans, Stefan Scheu

    Food webs in soil differ fundamentally from those aboveground; they are based on inputs from both living plants via root exudates, and from detritus, which is a complex mixture of fungi, bacteria, and dead plant remains. Trophic relationships are difficult to disentangle due to the cryptic lifestyle of soil animals and inevitable microbial contributions to their diet. Compound‐specific isotope analysis of amino acids (AAs) is increasingly used to explore complex food webs. The combined use of AA δ13C and δ15N values is a promising new approach to disentangle trophic relationships since it provides independent but complementary information on basal resources, as well as the trophic position of consumers. We conducted a controlled feeding study in which we reconstructed trophic chains from main basal resources (bacteria, fungi, plants) to primary consumers (springtails, oribatid mites) and predators (gamasid mites, spiders). We analyzed dual compound‐specific isotope AA values of both resources and consumers. By applying an approach termed “stable isotope (13C) fingerprinting” we identified basal resources, and concomitantly calculated trophic positions using 15N values of trophic and source AAs in consumers. In the 13C fingerprinting analysis, consumers in general grouped close to their basal resources. However, higher than usual offsets in AA δ13C between diet and consumers suggest either gut microbial supplementation or the utilization of specific resource fractions. Identification of trophic position crucially depends on correct estimates of the trophic discrimination factor (TDFGlu‐Phe), which was close to the commonly applied value of 7.6‰ in primary consumers feeding on microbial resources, but considerably lower in arachnid predators (~2.4‰), presumably due to higher diet quality, excretion of guanine, and fluid feeding. While our feeding study demonstrates that dual compound‐specific AA analyses hold great promise in delineating trophic linkages among soil‐dwelling consumers and their resources, it also highlights that a “one‐size‐fits‐all” approach to TDFGlu‐Phe does not apply to soil food webs.

    更新日期:2019-07-10
  • Plant responses to nutrient addition experiments conducted in tropical forests
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-07-09
    S. Joseph Wright

    I present a meta‐analysis of plant responses to 48 nutrient addition experiments conducted with native species in naturally growing tropical forests, exclusive of mangrove forests. The added nutrients include nitrogen (N) in 36 experiments, phosphorus (P) in 33 experiments, calcium and potassium in one experiment each, and various mixtures of essential nutrients in the remaining experiments. I evaluate the hypotheses that nutrients limit tropical forest plants, nutrient limitation is stronger in successional than in old‐growth forests, P but not N is limiting in lowland forests, and N is limiting in montane forests. Responses to the most complete nutrient mix used in each experiment were strong for plant functions that contribute to aboveground production (Hedges’ g averages 0.87) and nonsignificant for fine root biomass. Responses to N addition and to P addition were strong for tissue concentrations of the added element (Hedges’ g averages 0.75 and 1.4, respectively), moderate for fine litter production (0.64 and 0.65, respectively), moderate to weak for plant growth (0.46 and 0.37, respectively) and nonsignificant for fine root biomass. Growth responses were stronger in successional than in old‐growth forests. All responses were unrelated to elevation. The 48 experiments included 30 factorial nitrogen‐phosphorus experiments that enable additional direct tests of the widely cited hypotheses that P limitation is stronger than N limitation in lowland forests and vice versa in montane forests. Both hypotheses were rejected. The N × P interaction effect was nonsignificant across the factorial experiments. In conclusion, nutrients clearly limit tropical forest plants. Limitation by N is widespread in both lowland and montane forests, and the same is true for P. Single experiments identify limitation by calcium and potassium, and correlative studies suggest limitation by calcium, potassium, and magnesium. The available evidence is consistent with the possibility that most macronutrients limit tropical forest plants; however, experiments focus almost exclusively on N and P. The way forward will include taking fuller advantage of existing nutrient addition experiments, siting new experiments strategically, and developing cost‐effective methods to assay responses to all of the essential nutrients soils supply to plants.

    更新日期:2019-07-09
  • Novel bird responses to successive, large‐scale, landscape transformations
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-03-11
    David B. Lindenmayer, Wade Blanchard, Martin J. Westgate, Claire Foster, Sam C. Banks, Philip Barton, Mason Crane, Karen Ikin, Ben C. Scheele

    Transformation of intact vegetation into new kinds and configurations of human‐modified habitats is a well‐established driver of biodiversity loss. Following initial conversion, many human‐dominated landscapes are then subject to further large‐scale changes in land use. The impacts on biodiversity of repeated changes in land use remain poorly known, particularly how changes in the matrix interact with initial patterns of vegetation clearing. We used an 18‐yr study of birds in remnant patches of endangered temperate woodland in south‐eastern Australia to quantify the spatial and temporal effects of successive land use transformation in the surrounding landscape. We examined bird response to (1) initial patterns of landscape modification (creating semi‐cleared grazing land dominated by pastures that surrounded remnant woodland patches), (2) subsequent establishment and maturation of exotic tree plantations on the pastures surrounding woodland patches, and (3) additive and interactive effects of both types of landscape transformation. The majority of the 57 bird species modeled responded to conversion of grazing land to exotic plantations, either independently from initial patterns of landscape transformation (20 species), or interactively (18 species) or additively (15 species) with initial landscape transformation. The occurrence of only one species (the Common Bronzewing) was related to patterns of initial transformation but not subsequent transformation due to plantation establishment. Thus, despite many characteristics of the woodland patches within the plantation remaining largely unaltered throughout our 18‐yr investigation, the matrix had a profound effect on the kinds of species inhabiting them, with such impacts often magnified over time as the matrix continued to change. Plantation establishment triggered new regional‐level spatial processes with effects on birds detected in woodland patches up to 2 km away from the plantation. Matrix conversion selected for species with different traits (size, diet and movement patterns) compared to the initial transformation, suggesting it is acting as a different filter on the bird community. New kinds of landscape transformation (such as plantation establishment on previously cleared land) can radically affect the species that have persisted for many decades in previously modified landscapes. This highlights the challenges, but also opportunities, for conserving taxa in ever changing human‐dominated environments.

    更新日期:2019-07-05
  • Biases in studies of spatial patterns in insect herbivory
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-03-08
    Elena L. Zvereva, Mikhail V. Kozlov

    The properties of the human mind are responsible for a number of biases that affect the quality of scientific research. However, scientists working in the fields of ecology and environmental science rarely take these biases into account. We conducted a meta‐analysis of data extracted from 125 publications comparing woody plant damage by defoliating insects in different environments in order to understand the extent to which our knowledge on spatial patterns in herbivory is affected by various biases. We asked which research methods are most prone to biases and whether these biases lead to overestimation of the effects under study. The effect sizes (ESs) decreased with increases in the numbers of plant species involved in the study, with 61% lower ESs for herbivory estimated on all plants growing in study plots compared to herbivory on selected species. ESs also depended on the leaf sampling procedure: when all leaves from a tree or branch were sampled for measurements of herbivory or when random or systematic selection protocols were applied, ESs were 74% smaller than in cases of more subjective haphazard selection. In addition, ESs were 97% and 135% greater when the person conducting sampling and measuring was aware of the research hypothesis or sample origin, when compared with situations when the observer was blinded to these factors. The impacts of cognitive biases on the study outcomes significantly decreased with the increase in publication year; however, this pattern emerged mostly due to high‐ranked journals and was non‐significant for other journals. Using the studies of spatial patterns in herbivory as an example, we showed that our ecological and environmental knowledge is considerably biased due to an unconscious tendency of researchers to find support for their hypotheses and expectations, which generally leads to overestimation of the effects under study. Cognitive biases can be avoided by using different methods, such as applying randomization procedures in sampling and blinding of research hypotheses and sample origins. These measures should be seen as obligatory; otherwise, accumulation of the biased results in primary studies may ultimately lead to false general conclusions in subsequent research synthesis.

    更新日期:2019-07-05
  • Experimental nitrogen addition alters structure and function of a boreal bog: critical load and thresholds revealed
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-06-18
    R. Kelman Wieder, Dale H. Vitt, Melanie A. Vile, Jeremy A. Graham, Jeremy A. Hartsock, Hope Fillingim, Melissa House, James C. Quinn, Kimberli D. Scott, Meaghan Petix, Kelly J. McMillen

    Bogs and fens cover 6% and 21%, respectively, of the 140,329 km2 Oil Sands Administrative Area in northern Alberta. Development of the oil sands has led to increasing atmospheric N deposition, with values as high as 17 kg N·ha−1·yr−1; regional background deposition is <2 kg N·ha−1·yr−1. Bogs, being ombrotrophic, may be especially susceptible to increasing N deposition. To examine responses to N deposition, over five years, we experimentally applied N (as NH4NO3) to a bog near Mariana Lake, Alberta, unaffected by oil sands activities, at rates of 0, 5, 10, 15, 20, and 25 kg N·ha−1·yr−1, plus controls (no water or N addition). Increasing N addition: (1) stimulated N2 fixation at deposition <3.1 kg N·ha−1·yr−1, and progressively inhibited N2 fixation as N deposition increased above this level; (2) had no effect on Sphagnum fuscum net primary production (NPP) in years 1, 2, and 4, but inhibited S. fuscum NPP in years 3 and 5; (3) stimulated dominant shrub and Picea mariana NPP; (4) led to increased root biomass and production; (5) changed Sphagnum species relative abundance (decrease in S. fuscum, increase in S. magellanicum, no effect on S. angustifolium); (6) led to increasing abundance of Rhododendron groenlandicum and Andromeda polifolia, and to vascular plants in general; (7) led to increasing shrub leaf N concentrations in Andromeda polifolia, Chamaedaphne calyculata, Vaccinium oxycoccos, V. vitis‐idaea, and Picea mariana; (8) stimulated cellulose decomposition, with no effect on S. fuscum peat or mixed vascular plant litter decomposition; (9) had no effect on net N mineralization rates or on porewater NH4+‐N, NO3−‐N, or DON concentrations; and (10) had minimal effects on peat microbial community composition. Increasing experimental N addition led to a switch from new N being taken up primarily by Sphagnum to being taken up primarily by shrubs. As shrub growth and cover increase, Sphagnum abundance and NPP decrease. Because inhibition of N2 fixation by increasing N deposition plays a key role in bog structural and functional responses, we recommend a N deposition critical load of 3 kg N·ha−1·yr−1 for northern Alberta bogs.

    更新日期:2019-06-18
  • A comprehensive evaluation of predictive performance of 33 species distribution models at species and community levels
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-06-12
    Anna Norberg; Nerea Abrego; F. Guillaume Blanchet; Frederick R. Adler; Barbara J. Anderson; Jani Anttila; Miguel B. Araújo; Tad Dallas; David Dunson; Jane Elith; Scott D. Foster; Richard Fox; Janet Franklin; William Godsoe; Antoine Guisan; Bob O'Hara; Nicole A. Hill; Robert D. Holt; Francis K. C. Hui; Magne Husby; John Atle Kålås; Aleksi Lehikoinen; Miska Luoto; Heidi K. Mod; Graeme Newell; Ian Renner; Tomas Roslin; Janne Soininen; Wilfried Thuiller; Jarno Vanhatalo; David Warton; Matt White; Niklaus E. Zimmermann; Dominique Gravel; Otso Ovaskainen

    A large array of species distribution model (SDM) approaches has been developed for explaining and predicting the occurrences of individual species or species assemblages. Given the wealth of existing models, it is unclear which models perform best for interpolation or extrapolation of existing data sets, particularly when one is concerned with species assemblages. We compared the predictive performance of 33 variants of 15 widely applied and recently emerged SDMs in the context of multispecies data, including both joint SDMs that model multiple species together, and stacked SDMs that model each species individually combining the predictions afterward. We offer a comprehensive evaluation of these SDM approaches by examining their performance in predicting withheld empirical validation data of different sizes representing five different taxonomic groups, and for prediction tasks related to both interpolation and extrapolation. We measure predictive performance by 12 measures of accuracy, discrimination power, calibration, and precision of predictions, for the biological levels of species occurrence, species richness, and community composition. Our results show large variation among the models in their predictive performance, especially for communities comprising many species that are rare. The results do not reveal any major trade‐offs among measures of model performance; the same models performed generally well in terms of accuracy, discrimination, and calibration, and for the biological levels of individual species, species richness, and community composition. In contrast, the models that gave the most precise predictions were not well calibrated, suggesting that poorly performing models can make overconfident predictions. However, none of the models performed well for all prediction tasks. As a general strategy, we therefore propose that researchers fit a small set of models showing complementary performance, and then apply a cross‐validation procedure involving separate data to establish which of these models performs best for the goal of the study.

    更新日期:2019-06-12
  • Preferential sampling for presence/absence data and for fusion of presence/absence data with presence‐only data
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-06-10
    Alan E. Gelfand; Shinichiro Shirota

    Presence/absence data and presence‐only data are the two customary sources for learning about species distributions over a region. We present an ambitious agenda with regard to the analysis of such data. We illuminate the fundamental modeling differences between the two types of data. Most simply, locations are considered to be fixed under presence/absence data; locations are random under presence‐only data. The definition of “probability of presence” is incompatible between the two. We are not comfortable with modeling strategies in the literature that ignore this incompatibility and that assume that presence/absence modeling can be induced from presence‐only specifications and, therefore, that fusion of presence‐only and presence/absence data sources is routine. While, in some cases, data collection may not support this, we propose that, since, in nature, presence/absence is seen at the point locations, presence/absence data should be modeled at point level. If so, we need to specify two surfaces. The first provides the probability of presence at any location in the region. The second provides a realization from this surface in the form of a binary map yielding the results of Bernoulli trials across all locations; this surface is only partially observed. On the other hand, presence‐only data should be modeled as a (partially observed) point pattern, arising from a random number of individuals seen at random locations, driven by specification of an intensity function. There is no notion of Bernoulli trials; events are associated with areas. We further suggest that, with just presence/absence data, preferential sampling of locations may arise. Accounting for this, using a shared process perspective, can improve our estimated presence/absence surface as well as prediction of presence. We further propose that preferential sampling can enable a probabilistically coherent fusion of the two data types. We illustrate with two real data sets, one presence/absence, one presence‐only, for invasive species presence in New England in the United States. We demonstrate that potential bias in sampling locations can affect inference with regard to presence/absence and show that inference can be improved with preferential sampling ideas. We also provide a probabilistically coherent fusion of the two data sets again with the goal of improving inference for presence/absence. The importance of our work is to encourage more careful modeling when studying species distributions. Ignoring incompatibility between data types and adopting nongenerative modeling specifications results in invalid inference; the quantitative ecological community should benefit from this recognition.

    更新日期:2019-06-11
  • Propagule pressure and genetic diversity enhance colonization by a ruderal species: a multi‐generation field experiment
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-05-23
    Stephen M. Hovick; Kenneth D. Whitney

    Colonization is a critical filter, setting the stage for short‐term and long‐term population success. Increased propagule pressure (e.g., more founding individuals) usually enhances colonization; however, this pattern may be driven by purely numeric effects, population genetic diversity effects, or both. To determine the independent and interactive effects of propagule pressure and genetic diversity, we conducted a seed addition experiment in the field using the ruderal annual Arabidopsis thaliana. Propagule pressure treatments spanned five levels, from 32 to 960 seeds per 0.25‐m2 plot. Founder populations were composed of one, four, or eight genotypes and exposed to ambient or reduced levels of interspecific competition. Genotype monocultures were included to quantify additive vs. non‐additive effects. Populations were followed for three generations, with abundance, population persistence and genotype retention (the proportion of introduced genotypes persisting over time) as the major response variables. Increased propagule pressure enhanced abundance immediately following introduction, particularly where nutrient availability was high and competition reduced. Greater propagule pressure also increased the likelihood of population persistence and genotype retention through three generations. However, most populations experienced rapid abundance declines over time, yielding no relationship between propagule pressure and third‐generation abundance across persisting populations. Under reduced competition, increased genetic diversity led to a marginal increase in persistence through the third generation that was more pronounced, and statistically significant, in low nutrient conditions. Genetic diversity did not affect persistence through the first generation, thus indicating that genetic diversity effects strengthened over time. Nevertheless, genotypic mixture populations fell short of expectations based on performance in monocultures (negative non‐additive effects). Increased genetic diversity was also associated with abundance declines, largely due to one particularly high‐performing genotype in the lowest diversity treatments (i.e., genotypic identity effects). Overall, our results indicate that increases in both propagule pressure and genetic diversity can enhance colonization success but are highly context dependent. They also highlight novel ways in which both factors can impact the retention of introduced genetic diversity over time. Our findings pinpoint the determinants of a fundamental population process and have key implications for applications where enhanced or suppressed colonization is desired, including ecological restoration and invasive species management.

    更新日期:2019-05-24
  • Connected macroalgal‐sediment systems: blue carbon and food webs in the deep coastal ocean
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-05-23
    Ana Moura Queirós; Nicholas Stephens; Stephen Widdicombe; Karen Tait; Sophie J. McCoy; Jeroen Ingels; Saskia Rühl; Ruth Airs; Amanda Beesley; Giorgia Carnovale; Pierre Cazenave; Sarah Dashfield; Er Hua; Mark Jones; Penelope Lindeque; Caroline L. McNeill; Joana Nunes; Helen Parry; Christine Pascoe; Claire Widdicombe; Tim Smyth; Angus Atkinson; Dorte Krause‐Jensen; Paul J. Somerfield

    Macroalgae drive the largest CO2 flux fixed globally by marine macrophytes. Most of the resulting biomass is exported through the coastal ocean as detritus and yet almost no field measurements have verified its potential net sequestration in marine sediments. This gap limits the scope for the inclusion of macroalgae within blue carbon schemes that support ocean carbon sequestration globally, and the understanding of the role their carbon plays within distal food webs. Here, we pursued three lines of evidence (eDNA sequencing, Bayesian Stable Isotope Mixing Modeling, and benthic‐pelagic process measurements) to generate needed, novel data addressing this gap. To this end, a 13‐month study was undertaken at a deep coastal sedimentary site in the English Channel, and the surrounding shoreline of Plymouth, UK. The eDNA sequencing indicated that detritus from most macroalgae in surrounding shores occurs within deep, coastal sediments, with detritus supply reflecting the seasonal ecology of individual species. Bayesian stable isotope mixing modeling [C and N] highlighted its vital role in supporting the deep coastal benthic food web (22–36% of diets), especially when other resources are seasonally low. The magnitude of detritus uptake within the food web and sediments varies seasonally, with an average net sedimentary organic macroalgal carbon sequestration of 8.75 g C·m−2·yr−1. The average net sequestration of particulate organic carbon in sediments is 58.74 g C·m−2·yr−1, the two rates corresponding to 4–5% and 26–37% of those associated with mangroves, salt marshes, and seagrass beds, systems more readily identified as blue carbon habitats. These novel data provide important first estimates that help to contextualize the importance of macroalgal‐sedimentary connectivity for deep coastal food webs, and measured fluxes help constrain its role within global blue carbon that can support policy development. At a time when climate change mitigation is at the foreground of environmental policy development, embracing the full potential of the ocean in supporting climate regulation via CO2 sequestration is a necessity.

    更新日期:2019-05-23
  • Plant selection initiates alternative successional trajectories in the soil microbial community after disturbance
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-05-21
    Marie Duhamel; Joe Wan; Laura M. Bogar; R. Max Segnitz; Nora C. Duncritts; Kabir G. Peay

    Because interactions between plants and microbial organisms can influence species diversity and rates of nutrient cycling, how plants shape microbial communities is fundamental to understanding the structure of ecosystems. Despite this, the spatial and temporal scales over which plants influence microbial communities is poorly understood, particularly whether past abiotic or biotic legacies strongly constrain microbial community development. We examined biogeochemical cycling and microbial community structure in a coastal landscape where historical patterns of vegetation transition after a large fire in 1995 are well known, allowing us to account for past abiotic and biotic conditions. We found that alternative states in microbial community structure and ecosystem processes emerged under different plant species, regardless of past conditions. Greenhouse studies further demonstrated that these differences arise from direct plant selection of microbes, with selection stronger in roots compared with soils, especially for bacteria. Correlation of microbial community structure with seedling growth rates was also stronger for fungi compared to bacteria. Despite these effects, minimal overlap between seedling and field microbial communities indicates that the effects of initial plant selection are not stable; rather, plant selection initiated alternative successional trajectories after the fire. Using data from a guild where we have abundant natural history information, ectomycorrhizal fungi, we show that greenhouse communities are dominated by ruderal taxa that are also common in the field after the fire and that these ruderal fungi strongly alter spatial patterns in plant–soil feedback, enabling invasion and transformation of soils previously occupied by heterospecific plants, thus potentially acting as keystone mutualists.

    更新日期:2019-05-21
  • Regional variation in interior Alaskan boreal forests is driven by fire disturbance, topography, and climate
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-05-20
    Carl A. Roland; Joshua H. Schmidt; Samantha G. Winder; Sarah E. Stehn; E. Fleur Nicklen

    High latitude regions are warming rapidly with important ecological and societal consequences. Utilizing two landscape‐scale data sets from interior Alaska, we compared patterns in forest structure in two regions with differing fire disturbance, topography, and summer climate norms. Our goal was to evaluate a set of hypotheses concerning possible warming‐driven changes in forest structure suggested by recent literature. We found essentially consistent habitat associations for the tree flora across two disparate study areas concomitant with considerable differences in observed patterns of forest structure and composition. Our results confirmed expected increases in broadleaved species occupancy and abundance in the warmer, more fire‐affected study region along with considerably higher tree occupancy and abundance in high elevation areas there. However, contrary to our predictions, we found no evidence of expected reductions in conifer occupancy or increases in non‐fire related tree mortality. Instead, both individual and combined tree species occupancy, density, abundance, and richness were considerably higher in the warmer, more fire‐influenced region, except in the warmest, driest areas (steep and south‐facing slopes at low elevation). Our comparison of two landscape‐scale data sets suggests that changes in tree distribution and forest structure in interior Alaska will proceed unevenly, governed by a mosaic of site‐dependent influences wherein forest community composition and species dominance will shift along different trajectories and at different rates according to variation in underlying landscape attributes. Although there were clear differences in forest structure between the two areas that were likely attributable to differences in growing season warmth and fire disturbance, we found scant support for the concept of an incipient, ongoing biome shift in interior Alaska resulting from impending diminution of boreal forest cover over the short to medium term. Indeed, we suggest that (depending on severity of disturbance dynamics and the rapidity of future warming) cooler areas of interior Alaska's forest may reasonably be expected to sustain marginal increases in forest cover with additional warming, at least in certain topographic positions (such as poorly drained basins and cool treeline sites) and/or geographic regions, prior to any landscape‐scale diminution of forest cover due to warming.

    更新日期:2019-05-20
  • Indirect legacy effects of an extreme climatic event on a marine megafaunal community
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-04-25
    Robert Nowicki; Michael Heithaus; Jordan Thomson; Derek Burkholder; Kirk Gastrich; Aaron Wirsing

    While extreme climatic events (ECEs) are predicted to become more frequent, reliably predicting their impacts on consumers remains challenging, particularly for large consumers in marine environments. Many studies that do evaluate ECE effects focus primarily on direct effects, though indirect effects can be equally or more important. Here, we investigate the indirect impacts of the 2011 “Ningaloo Niño” marine heatwave ECE on a diverse megafaunal community in Shark Bay, Western Australia. We use an 18‐year community‐level data set before (1998–2010) and after (2012–2015) the heatwave to assess the effects of seagrass loss on the abundance of seven consumer groups: sharks, sea snakes (multiple species), Indo‐pacific bottlenose dolphins (Tursiops aduncus), dugongs (Dugong dugon), green turtles (Chelonia mydas), loggerhead turtles (Caretta caretta), and Pied Cormorants (Phalacrocorax spp.). We then assess whether seagrass loss influences patterns of habitat use by the latter five groups, which are under risk of shark predation. Sharks catch rates were dominated by the generalist tiger shark (Galeocerdo cuvier) and changed little, resulting in constant apex predator density despite heavy seagrass degradation. Abundances of most other consumers declined markedly as food and refuge resources vanished, with the exception of generalist loggerhead turtles. Several consumer groups significantly modified their habitat use patterns in response to the die‐off, but only bottlenose dolphins did so in a manner suggestive of a change in risk‐taking behavior. We show that ECEs can have strong indirect effects on megafauna populations and habitat use patterns in the marine environment, even when direct effects are minimal. Our results also show that indirect impacts are not uniform across taxa or trophic levels and suggest that generalist marine consumers are less susceptible to indirect effects of ECEs than specialists. Such non‐uniform changes in populations and habitat use patterns have implications for community dynamics, such as the relative strength of direct predation and predation risk. Attempts to predict ecological impacts of ECEs should recognize that direct and indirect effects often operate through different pathways and that taxa can be strongly impacted by one even if resilient to the other.

    更新日期:2019-05-16
  • IPM2: toward better understanding and forecasting of population dynamics
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-03-28
    Floriane Plard; Daniel Turek; Martin U. Grüebler; Michael Schaub

    Dynamic population models typically aim to predict demography and the resulting population dynamics in relation to environmental variation. However, they rarely include the diversity of individual responses to environmental changes, thus hampering our understanding of demographic mechanisms. We develop an integrated integral projection model (IPM2) that is a combination of an integrated population model (IPMpop) and an integral projection model (IPMind). IPM2 includes interactions between environmental and individual effects on demographic rates and can forecast both population size and individual trait distributions. First, we study the performance of this model using eight simulated scenarios with variable reproductive selective pressures on an individual trait. When the individual trait interacts with the environmental variable and the selective pressure on the individual trait is nonlinear, only IPM2 produces adequate predictions, because IPMind does not link predictions between the population level and observed data and because IPMpop does not include the individual trait. Second, we apply IPM2 to a population of barn swallows. The model accurately predicts trends of the barn swallow population while also providing mechanistic insights. High precipitation negatively influenced population dynamics through delaying laying dates, which lowered reproductive and survival rates. To predict the future of populations, we need to understand their individual drivers and thus include individual responses to their environment while following the entire population. As a consequence, IPM2 will improve our ability to test ecological and evolutionary hypotheses and improve the accuracy of population forecasting to aid management programs.

    更新日期:2019-05-16
  • Emerging reservoir delta‐backwaters: biophysical dynamics and riparian biodiversity
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-03-19
    Malia A. Volke; W. Carter Johnson; Mark D. Dixon; Michael L. Scott

    Deltas and backwater‐affected bottomlands are forming along tributary and mainstem confluences in reservoirs worldwide. Emergence of prograding deltas, along with related upstream hydrogeomorphic changes to river bottomlands in the backwater fluctuation zones of reservoirs, signals the development of new and dynamic riparian and wetland habitats. This study was conducted along the regulated Missouri River, USA, to examine delta‐backwater formation and describe vegetation response to its development and dynamics. Our research focused specifically on the delta‐backwater forming at the confluence of the White River tributary and Lake Francis Case reservoir. Objectives of the research were to: (1) describe and analyze the process of delta‐backwater formation over space and time; (2) determine by field sampling and GIS mapping how vegetation has responded to development of the delta‐backwater; and (3) compare the woody plant communities of the delta‐backwater to those along free‐flowing and regulated remnant river reaches. In response to base level changes caused by reservoir filling, the thalweg of the lower 31 km of the original White River channel and adjacent floodplain aggraded by up to 12 m between 1954 and 2011. The overall channel slope flattened from 0.70 to 0.29 m/km. Riparian Populus–Salix forests increased in area by nearly 50% during the post‐dam period by colonizing new deltaic and floodplain deposits. Many of the native woody species found along natural and regulated river reaches were also found on the delta‐backwater. Woody species sorted along a fluvial to delta gradient; wetland affiliated species (Salix spp., Typha spp.) dominated the delta‐backwater near the reservoir while riparian species (Populus, Fraxinus) dominated in upstream portions of the delta‐backwater. This habitat complex supports young stands of native riparian vegetation now in decline in remnant reaches protected from flooding.

    更新日期:2019-05-16
  • Eighteen years of ecological monitoring reveals multiple lines of evidence for tundra vegetation change
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-03-12
    Isla H. Myers‐Smith; Meagan M. Grabowski; Haydn J. D. Thomas; Sandra Angers‐Blondin; Gergana N. Daskalova; Anne D. Bjorkman; Andrew M. Cunliffe; Jakob J. Assmann; Joseph S. Boyle; Edward McLeod; Samuel McLeod; Ricky Joe; Paden Lennie; Deon Arey; Richard R. Gordon; Cameron D. Eckert

    The Arctic tundra is warming rapidly, yet the exact mechanisms linking warming and observed ecological changes are often unclear. Understanding mechanisms of change requires long‐term monitoring of multiple ecological parameters. Here, we present the findings of a collaboration between government scientists, local people, park rangers, and academic researchers that provide insights into changes in plant composition, phenology, and growth over 18 yr on Qikiqtaruk‐Herschel Island, Canada. Qikiqtaruk is an important focal research site located at the latitudinal tall shrub line in the western Arctic. This unique ecological monitoring program indicates the following findings: (1) nine days per decade advance of spring phenology, (2) a doubling of average plant canopy height per decade, but no directional change in shrub radial growth, and (3) a doubling of shrub and graminoid abundance and a decrease by one‐half in bare ground cover per decade. Ecological changes are concurrent with satellite‐observed greening and, when integrated, suggest that indirect warming from increased growing season length and active layer depths, rather than warming summer air temperatures alone, could be important drivers of the observed tundra vegetation change. Our results highlight the vital role that long‐term and multi‐parameter ecological monitoring plays in both the detection and attribution of global change.

    更新日期:2019-03-13
  • Dominance network analysis provides a new framework for studying the diversity–stability relationship
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-03-06
    Zhanshan (Sam) Ma; Aaron M. Ellison

    The diversity–stability relationship is a long‐standing, central focus of community ecology. Two major challenges have impeded studies of the diversity–stability relationship (DSR): the difficulty in obtaining high‐quality longitudinal data sets; and the lack of a general theoretical framework that can encompass the enormous complexity inherent in “diversity,” “stability,” and their many interactions. Metagenomic “Big Data” now provide high quality longitudinal data sets, and the human microbiome project (HMP) offers an unprecedented opportunity to reinvigorate investigations of DSRs. We introduce a new framework for exploring DSRs that has three parts: (1) a cross‐scale measure of dominance with a simple mathematical form that can be applied simultaneously to individual species and entire communities and can be used to construct species dominance networks (SDNs); (2) analysis of SDNs based on special trio motifs, core‐periphery, rich‐club, and nested structures, and high salience skeletons; and (3) a synthesis of coarse‐scale core/periphery/community‐level stability modeling with fine‐scale analysis of SDNs that further reveals the stability properties of the community structures. We apply this new approach to data from the human vaginal microbiome of the HMP, simultaneously illustrating its utility in developing and testing theories of diversity and stability while providing new insights into the underlying ecology and etiology of a human microbiome‐associated disease.

    更新日期:2019-03-07
  • The intrinsic predictability of ecological time series and its potential to guide forecasting
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-03-05
    Frank Pennekamp; Alison C. Iles; Joshua Garland; Georgina Brennan; Ulrich Brose; Ursula Gaedke; Ute Jacob; Pavel Kratina; Blake Matthews; Stephan Munch; Mark Novak; Gian Marco Palamara; Björn C. Rall; Benjamin Rosenbaum; Andrea Tabi; Colette Ward; Richard Williams; Hao Ye; Owen L. Petchey

    Successfully predicting the future states of systems that are complex, stochastic, and potentially chaotic is a major challenge. Model forecasting error (FE) is the usual measure of success; however model predictions provide no insights into the potential for improvement. In short, the realized predictability of a specific model is uninformative about whether the system is inherently predictable or whether the chosen model is a poor match for the system and our observations thereof. Ideally, model proficiency would be judged with respect to the systems’ intrinsic predictability, the highest achievable predictability given the degree to which system dynamics are the result of deterministic vs. stochastic processes. Intrinsic predictability may be quantified with permutation entropy (PE), a model‐free, information‐theoretic measure of the complexity of a time series. By means of simulations, we show that a correlation exists between estimated PE and FE and show how stochasticity, process error, and chaotic dynamics affect the relationship. This relationship is verified for a data set of 461 empirical ecological time series. We show how deviations from the expected PE–FE relationship are related to covariates of data quality and the nonlinearity of ecological dynamics. These results demonstrate a theoretically grounded basis for a model‐free evaluation of a system's intrinsic predictability. Identifying the gap between the intrinsic and realized predictability of time series will enable researchers to understand whether forecasting proficiency is limited by the quality and quantity of their data or the ability of the chosen forecasting model to explain the data. Intrinsic predictability also provides a model‐free baseline of forecasting proficiency against which modeling efforts can be evaluated.

    更新日期:2019-03-06
  • Multiple mechanisms confer stability to isolated populations of a rare endemic plant
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-03-04
    Reilly R. Dibner; Megan L. Peterson; Allison M. Louthan; Daniel F. Doak

    The persistence of small populations remains a puzzle for ecology and conservation. Especially interesting is how naturally small, isolated populations are able to persist in the face of multiple environmental forces that create fluctuating conditions and should, theory predicts, lead to high probabilities of extirpation. We used a combination of long‐term census data and a five‐year demographic study of a naturally rare, endemic plant, Yermo xanthocephalus, to evaluate the importance of several possible mechanisms for small population persistence: negative density dependence, vital rate buffering, demographic compensation, asynchrony in dynamics among sub‐populations, and source–sink dynamics. These non‐exclusive explanations for population persistence all have been shown to operate in some systems, but have rarely if ever been simultaneously examined for the same population or species. We hypothesized that asynchrony in dynamics and demographic compensation would be more powerful than the other three mechanisms. We found partial support for our hypothesis: density dependence, asynchrony among population segments, and source–sink patterns appear to be the most important mechanisms maintaining population viability in this species. Importantly, these processes all appear to operate strongly at very fine spatial scales for Yermo, allowing the only two, extremely small, populations to persist. We also found considerable differences in the results of our census and demographic analyses. In general, we estimated substantially greater chances of population survival from the census data than from the shorter‐term demographic studies. In part, this difference is due to drier than average climate conditions during the years of the demographic work. These results emphasize that while demographic information is necessary to understand various components of population dynamics, longer term studies, even if much less detailed, can be more powerful in uncovering some mechanisms that may be critical in stabilizing population numbers, especially in variable environments.

    更新日期:2019-03-04
  • Spatially structured statistical network models for landscape genetics
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-02-27
    Erin E. Peterson; Ephraim M. Hanks; Mevin B. Hooten; Jay M. Ver Hoef; Marie‐Josée Fortin

    A basic understanding of how the landscape impedes, or creates resistance to, the dispersal of organisms and hence gene flow is paramount for successful conservation science and management. Spatially structured ecological networks are often used to represent spatial landscape‐genetic relationships, where nodes represent individuals or populations and resistance to movement is represented using non‐binary edge weights. Weights are typically assigned or estimated by the user, rather than observed, and validating such weights is challenging. We provide a synthesis of current methods used to estimate edge weights and an overview of common model types, stressing the advantages and disadvantages of each approach and their ability to model landscape‐genetic data. We further explore a set of spatial‐statistical methods that provide ecologists with alternative approaches for modeling spatially explicit processes that may affect genetic structure. This includes an overview of spatial autoregressive models, with a particular focus on how correlation and partial correlation are used to represent neighborhood structure with the inverse of the covariance matrix (i.e., precision matrix). We then demonstrate how to model resistance by specifying an appropriate statistical model on the nodes, conditioned on the edge weights, through the precision matrix. This integration of network ecology and spatial statistics provides a practical analytical framework for landscape‐genetic studies. The results can be used to make statistical inferences about the relative importance of individual landscape characteristics, such as the vegetative cover, hillslope, or the presence of roads or rivers, on gene flow. In addition, the R code we include allows readers to explore landscape‐genetic structure in their own datasets, which will potentially provide new insights into the evolutionary processes that generated ecological networks, as well as valuable information about the optimal characteristics of conservation corridors.

    更新日期:2019-02-28
  • Phylofactorization: a graph partitioning algorithm to identify phylogenetic scales of ecological data
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-02-19
    Alex D. Washburne; Justin D. Silverman; James T. Morton; Daniel J. Becker; Daniel Crowley; Sayan Mukherjee; Lawrence A. David; Raina K. Plowright

    The problem of pattern and scale is a central challenge in ecology. In community ecology, an important scale is that at which we aggregate species to define our units of study, such as aggregation of “nitrogen fixing trees” to understand patterns in carbon sequestration. With the emergence of massive community ecological data sets, there is a need to objectively identify the scales for aggregating species to capture well‐defined patterns in community ecological data. The phylogeny is a scaffold for identifying scales of species‐aggregation associated with macroscopic patterns. Phylofactorization was developed to identify phylogenetic scales underlying patterns in relative abundance data, but many ecological data, such as presence‐absences and counts, are not relative abundances yet may still have phylogenetic scales capturing patterns of interest. Here, we broaden phylofactorization to a graph‐partitioning algorithm identifying phylogenetic scales in community ecological data. As a graph‐partitioning algorithm, phylofactorization connects many tools from data analysis to phylogenetically informed analyses of community ecological data. Two‐sample tests identify five phylogenetic factors of mammalian body mass which arose during the K‐Pg extinction event, consistent with other analyses of mammalian body mass evolution. Projection of data onto coordinates connecting the phylogeny and graph‐partitioning algorithm yield a phylogenetic principal components analysis which refines our understanding of the major sources of variation in the human gut microbiome. These same coordinates allow generalized additive modeling of microbes in Central Park soils, confirming that a large clade of Acidobacteria thrive in neutral soils. The graph‐partitioning algorithm extends to generalized linear and additive modeling of exponential family random variables by phylogenetically constrained reduced‐rank regression or stepwise factor contrasts. All of these tools can be implemented with the R package phylofactor.

    更新日期:2019-02-19
  • Nitrogen deposition and climate change effects on tree species composition and ecosystem services for a forest cohort
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-02-05
    George Van Houtven; Jennifer Phelan; Christopher Clark; Robert D. Sabo; John Buckley; R. Quinn Thomas; Kevin Horn; Stephen D. LeDuc

    The composition of forests in the northeastern United States and the ecosystem services they provide to future generations will depend on several factors. In this paper, we isolate the effects of two environmental drivers, nitrogen (N) deposition and climate (temperature and precipitation) change, through an analysis of a single cohort of 24 dominant tree species. We assembled a tree database using data from U.S. Forest Service Forest Inventory and Analysis monitoring plots. Applying observed species‐specific growth and survival responses, we simulated how forest stands in a 19‐state study area would change from 2005 to 2100 under 12 different future N deposition–climate scenarios. We then estimated implications for three selected forest ecosystem services: merchantable timber, aboveground carbon sequestration, and tree diversity. Total tree biomass (for 24 species combined) was positively associated with both increased N deposition and temperatures; however, due to differences in the direction and magnitude of species‐specific responses, forest composition varied across scenarios. For example, red maple (Acer rubrum) trees gained biomass under scenarios with more N deposition and more climate change, whereas biomass of yellow birch (Betula alleghaniensis) and red pine (Pinus resinosa) was negatively affected. Projections for ecosystem services also varied across scenarios. Carbon sequestration, which is positively associated with biomass accumulation, increased with N deposition and increasing climate change. Total timber values also increased with overall biomass; however, scenarios with increasing climate change tended to favor species with lower merchantable value, whereas more N deposition favored species with higher merchantable value. Tree species diversity was projected to decrease with greater changes in climate (warmer temperatures), especially in the northwestern, central, and southeastern portions of the study area. In contrast, the effects of N deposition on diversity varied greatly in magnitude and direction across the study area. This study highlights species‐specific and regional effects of N deposition and climate change in northeastern U.S. forests, which can inform management decision for air quality and forests in the region, as well as climate policy. It also provides a foundation for future studies that may incorporate other important factors such as multiple cohorts, sulfur deposition, insects, and diseases.

    更新日期:2019-02-05
  • Size, weapons, and armor as predictors of competitive outcomes in fossil and contemporary marine communities
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-02-01
    L. H. Liow; T. Reitan; K. L. Voje; P. D. Taylor; E. Di Martino

    Inter‐ and intraspecific competition are usually observed over a few generations but their patterns and consequences are seldom tractable in natural systems over longer timescales relevant to macroevolutionary change. Here, we use win‐draw‐lose competitive overgrowths for a marine benthic community of encrusting bryozoans that have evolved together in New Zealand for at least 2.3 million years to investigate battles for substrate space, a resource that is limiting for these colonial organisms. Using more than 6,000 fossilized and contemporary battles, we explored what combination of traits—including relative zooid (module) size, weapons, armor, and relative abundance—best predict battle outcomes, and if these are time varying. In simpler models, where we disregard trait–trait interactions, we find that the effects of larger zooid sizes and three‐dimensional growth on battle outcomes are both positive, while that of relative abundance is negative, such that more common species are more often overgrown by less common species. When we include trait–trait and trait–time interactions in our models, we confirm that a larger zooid size is advantageous for successful overgrowth but infer that it is time varying. In these complex models, we also detect interactions between combinations of traits, where more armored and weaponized bryozoans seem to be at a disadvantage in overgrowth battles. Our best models do perform statistically better than the null model, but we find that there is low predictability for overgrowth outcomes for our New Zealand data set of fossil and contemporary battles, suggesting unmeasured variables and/or high stochasticity in a system that is otherwise well characterized. A best model, developed using our New Zealand data, is applied to three ecologically similar systems described in previous studies to investigate its general predictive power, with the expectation that it would perform better than null models. Surprisingly, we find that the best model developed within the New Zealand system cannot be extrapolated to other encrusting cheilostome bryozoan communities and that these three communities often even have opposite signs for trait coefficients. We conclude that there is much to learn about multi‐species marine communities where biotic interactions such as competition may have long‐lasting consequences for ecological and evolutionary dynamics.

    更新日期:2019-02-05
  • Phenology as a process rather than an event: from individual reaction norms to community metrics
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-02-01
    Brian D. Inouye; Johan Ehrlén; Nora Underwood

    Measures of the seasonal timing of biological events are key to addressing questions about how phenology evolves, modifies species interactions, and mediates biological responses to climate change. Phenology is often characterized in terms of discrete events, such as a date of first flowering or arrival of first migrants. We discuss how phenological events that are typically measured at the population or species level arise from distributions of phenological events across seasons, and from norms of reaction of these phenological events across environments. We argue that individual variation in phenological distributions and reaction norms has important implications for how we should collect, analyze, and interpret phenological information. Regarding phenology as a reaction norm rather than one year's specific values implies that selection acts on the phenologies that an individual expresses over its lifetime. To understand how climate change is likely to influence phenology, we need to consider not only plastic responses along the reaction norm but changes in the reaction norm itself. We show that when individuals vary in their reaction norms, correlations between reaction norm elevation and slope make first events particularly poor estimators of population sensitivity to climate change, and variation in slopes can obscure the pattern of selection on phenology. We also show that knowing the shape of the distribution of phenological events across the season is important for predicting biologically important phenological mismatches with climate change. Last, because phenological events are parts of a continuous developmental process, we suggest that the approach of measuring phenology by recording developmental stages of individuals in a population at a single point in time should be used more widely. We conclude that failure to account for phenological distributions and reaction norms may lead to overinterpretation of metrics based on single events, such as commonly recorded first event dates, and may confound meta‐analyses that use a range of metrics. Rather than prescribing a single universal approach to studying phenology, we point out limitations of inferences based on single metrics and encourage work that considers the multivariate nature of phenology and more tightly links data collection and analyses with biological hypotheses.

    更新日期:2019-02-05
  • A comprehensive analysis of autocorrelation and bias in home range estimation
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-31
    Michael J. Noonan; Marlee A. Tucker; Christen H. Fleming; Thomas S. Akre; Susan C. Alberts; Abdullahi H. Ali; Jeanne Altmann; Pamela Castro Antunes; Jerrold L. Belant; Dean Beyer; Niels Blaum; Katrin Böhning‐Gaese; Laury Cullen; Rogerio Cunha de Paula; Jasja Dekker; Jonathan Drescher‐Lehman; Nina Farwig; Claudia Fichtel; Christina Fischer; Adam T. Ford; Jacob R. Goheen; René Janssen; Florian Jeltsch; Matthew Kauffman; Peter M. Kappeler; Flávia Koch; Scott LaPoint; A. Catherine Markham; Emilia Patricia Medici; Ronaldo G. Morato; Ran Nathan; Luiz Gustavo R. Oliveira‐Santos; Kirk A. Olson; Bruce D. Patterson; Agustin Paviolo; Emiliano Esterci Ramalho; Sascha Rösner; Dana G. Schabo; Nuria Selva; Agnieszka Sergiel; Marina Xavier da Silva; Orr Spiegel; Peter Thompson; Wiebke Ullmann; Filip Zięba; Tomasz Zwijacz‐Kozica; William F. Fagan; Thomas Mueller; Justin M. Calabrese

    Home range estimation is routine practice in ecological research. While advances in animal tracking technology have increased our capacity to collect data to support home range analysis, these same advances have also resulted in increasingly autocorrelated data. Consequently, the question of which home range estimator to use on modern, highly autocorrelated tracking data remains open. This question is particularly relevant given that most estimators assume independently sampled data. Here, we provide a comprehensive evaluation of the effects of autocorrelation on home range estimation. We base our study on an extensive data set of GPS locations from 369 individuals representing 27 species distributed across five continents. We first assemble a broad array of home range estimators, including Kernel Density Estimation (KDE) with four bandwidth optimizers (Gaussian reference function, autocorrelated‐Gaussian reference function [AKDE], Silverman's rule of thumb, and least squares cross‐validation), Minimum Convex Polygon, and Local Convex Hull methods. Notably, all of these estimators except AKDE assume independent and identically distributed (IID) data. We then employ half‐sample cross‐validation to objectively quantify estimator performance, and the recently introduced effective sample size for home range area estimation ( N ^ area ) to quantify the information content of each data set. We found that AKDE 95% area estimates were larger than conventional IID‐based estimates by a mean factor of 2. The median number of cross‐validated locations included in the hold‐out sets by AKDE 95% (or 50%) estimates was 95.3% (or 50.1%), confirming the larger AKDE ranges were appropriately selective at the specified quantile. Conversely, conventional estimates exhibited negative bias that increased with decreasing N ^ area . To contextualize our empirical results, we performed a detailed simulation study to tease apart how sampling frequency, sampling duration, and the focal animal's movement conspire to affect range estimates. Paralleling our empirical results, the simulation study demonstrated that AKDE was generally more accurate than conventional methods, particularly for small N ^ area . While 72% of the 369 empirical data sets had >1,000 total observations, only 4% had an N ^ area >1,000, where 30% had an N ^ area <30. In this frequently encountered scenario of small N ^ area , AKDE was the only estimator capable of producing an accurate home range estimate on autocorrelated data.

    更新日期:2019-01-31
  • Trajectory analysis in community ecology
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-31
    Miquel De Cáceres; Lluís Coll; Pierre Legendre; Robert B. Allen; Susan K. Wiser; Marie‐Josée Fortin; Richard Condit; Stephen Hubbell

    Ecologists have long been interested in how communities change over time. Addressing questions about community dynamics requires ways of representing and comparing the variety of dynamics observed across space. Until now, most analytical frameworks have been based on the comparison of synchronous observations across sites and between repeated surveys. An alternative perspective considers community dynamics as trajectories in a chosen space of community resemblance and utilizes trajectories as objects to be analyzed and compared using their geometry. While methods that take this second perspective exist, for example to test for particular trajectory shapes, there is a need for formal analytical frameworks that fully develop the potential of this approach. By adapting concepts and procedures used for the analysis of spatial trajectories, we present a framework for describing and comparing community trajectories. A key element of our contribution is the means to assess the geometric resemblance between trajectories, which allows users to describe, quantify, and analyze variation in community dynamics. We illustrate the behavior of our framework using simulated data and two spatiotemporal community data sets differing in the community properties of interest (species composition vs. size distribution of individuals). We conclude by evaluating the advantages and limitations of our community trajectory analysis framework, highlighting its broad domain of application and anticipating potential extensions.

    更新日期:2019-01-31
  • Temporal variation in resource selection of African elephants follows long‐term variability in resource availability
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-29
    Miriam Tsalyuk; Werner Kilian; Björn Reineking; Wayne Marcus Getz

    The relationship between resource availability and wildlife movement patterns is pivotal to understanding species behavior and ecology. Movement response to landscape variables occurs at multiple temporal scales, from sub‐diurnal to multiannual. Additionally, individuals may respond to both current and past conditions of resource availability. In this paper, we examine the temporal scale and variation of current and past resource variables that affect movement patterns of African elephants (Loxodonta africana) using sub‐hourly movement data from GPS‐GSM collared elephants in Etosha National Park, Namibia. We created detailed satellite‐based spatiotemporal maps of vegetation biomass, as well as distance from surface water, road and fence. We used step selection functions to measure the relative importance of these landscape variables in determining elephants’ local movement patterns. We also examined how elephants respond to information, in locations they have previously visited, on productivity integrated over different temporal scales: from current to historical conditions. Our results demonstrate that elephants choose patches with higher than average annual productivity and grass biomass, but lower tree biomass. Elephants also prefer to walk close to water, roads, and fences. These preferences vary with time of day and with season, thereby providing insights into diurnal and seasonal behavioral patterns and the ecological importance of the landscape variables examined. We also discovered that elephants respond more strongly to long‐term patterns of productivity than to immediate forage conditions, in familiar locations. Our results illustrate how animals with high cognitive capacity and spatial memory integrate long‐term information on landscape conditions. We illuminate the importance of long‐term high temporal resolution satellite imagery to understanding the relationship between movement patterns and landscape structure.

    更新日期:2019-01-30
  • Range‐wide populations of a long‐distance migratory songbird converge during stopover in the tropics
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-25
    Camila Gómez; Sara L. Guerrero; Alyssa M. FitzGerald; Nicholas J. Bayly; Keith A. Hobson; Carlos Daniel Cadena

    Geographic convergence during migration influences the extent to which animal populations may experience carry‐over effects across periods of the annual cycle. When most individuals of a population share geographic areas during a given priod, carry‐over effects are likely stronger than when individuals occupy multiple areas. We used genetic data and stable isotope (δ2H) measurements from feathers and claws to describe the likely breeding and wintering geographic origins of a long‐distance migratory songbird (Gray‐cheeked Thrush, Catharus minimus) moving through northern Colombia in spring and fall migration. Furthermore, we used these data coupled with regional occupancy surveys to assess whether individuals from various breeding populations converge during migration and evaluated whether geographic origin, age, or sex affected stopover strategies. We found that range‐wide breeding populations of Gray‐cheeked Thrush converged in northern Colombia in an area spanning <1% of the breeding range, especially during a prolonged spring stopover in the Sierra Nevada de Santa Marta. Breeding (but not winter) origin, sex, and age influenced arrival date and body condition upon arrival at stopover sites where populations converged. Birds from more northerly breeding latitudes, males and adults generally arrived earlier and in lower body condition than those with more southerly breeding origins, females, and juveniles. Our work and other studies suggest that areas in northern Colombia may function as ecological bottlenecks for Gray‐cheeked Thrush because they concentrate individuals from across the breeding range, provide critical resources, and impose constraints during migration. Future studies quantifying the effects of high‐convergence areas on fitness and survival of individuals and their demographic consequences are required to assess their roles as ecological bottlenecks.

    更新日期:2019-01-25
  • An attribute‐diversity approach to functional diversity, functional beta diversity, and related (dis)similarity measures
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-25
    Anne Chao; Chun‐Huo Chiu; Sébastien Villéger; I‐Fang Sun; Simon Thorn; Yi‐Ching Lin; Jyh‐Min Chiang; William B. Sherwin

    Based on the framework of attribute diversity (a generalization of Hill numbers of order q), we develop a class of functional diversity measures sensitive not only to species abundances but also to trait‐based species‐pairwise functional distances. The new method refines and improves on the conventional species‐equivalent approach in three areas: (1) the conventional method often gives similar values (close to unity) to assemblages with contrasting levels of functional diversity; (2) when a distance metric is unbounded, the conventional functional diversity depends on the presence/absence of other assemblages in the study; (3) in partitioning functional gamma diversity into alpha and beta components, the conventional gamma is sometimes less than alpha. To resolve these issues, we add to the attribute‐diversity framework a novel concept: τ, the threshold of functional distinctiveness between any two species; here, τ can be chosen to be any positive value. Any two species with functional distance ≥ τ are treated as functionally equally distinct. Our functional diversity quantifies the effective number of functionally equally distinct species (or “virtual functional groups”) with all pairwise distances at least τ for different species pairs. We advocate the use of two complementary diversity profiles (τ profile and q profile), which depict functional diversity with varying levels of τ and q, respectively. Both the conventional species‐equivalent method (i.e., τ is the maximum of species‐pairwise distances) and classic taxonomic diversity (i.e., τ is the minimum of non‐zero species‐pairwise distances) are incorporated into our proposed τ profile for an assemblage. For any type of species‐pairwise distance matrices, our attribute‐diversity approach allows proper diversity partitioning, with the desired property gamma ≥ alpha and thus avoids all the restrictions that apply to the conventional diversity decomposition. Our functional alpha and gamma are interpreted as the effective numbers of functionally equally distinct species, respectively, in an assemblage and in the pooled assemblage, while beta is the effective number of equally large assemblages with no shared species and all species in the assemblages being equally distinct. The resulting beta diversity can be transformed to obtain abundance‐sensitive Sørensen‐ and Jaccard‐type functional (dis)similarity profiles. Hypothetical and real examples are used to illustrate the framework. Online software and R codes are available to facilitate computations.

    更新日期:2019-01-25
  • Structure and function of the bacterial and fungal gut microbiota of Neotropical butterflies
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-22
    Alison Ravenscraft; Michelle Berry; Tobin Hammer; Kabir Peay; Carol Boggs

    The relationship between animals and their gut flora is simultaneously one of the most common and most complex symbioses on Earth. Despite its ubiquity, our understanding of this invisible but often critical relationship is still in its infancy. We employed adult Neotropical butterflies as a study system to ask three questions: First, how does gut microbial community composition vary across host individuals, species and dietary guilds? Second, how do gut microbiota compare to food microbial communities? Finally, are gut flora functionally adapted to the chemical makeup of host foods? To answer these questions we captured nearly 300 Costa Rican butterflies representing over 50 species, six families, and two feeding guilds: frugivores and nectivores. We characterized bacteria and fungi in guts, wild fruits, and wild nectars via amplicon sequencing and assessed the catabolic abilities of the gut microbiota via culture‐based assays. Gut communities were distinct from food communities, suggesting that the gut environment acts as a filter on potential colonists. Nevertheless, gut flora varied widely among individuals and species. On average, a pair of butterflies shared 21% of their bacterial species and 6% of their fungi. Host species explained 25–30% of variation in microbial communities while host diet explained 4%, suggesting that non‐dietary aspects of host biology play a large role in structuring the butterfly gut flora. Much of the variation between species correlated with host phylogeny. Host diet was related to gut microbial function: compared to frugivores, nectivores’ gut flora exhibited increased catabolism of sugars and sugar alcohols and decreased catabolism of amino acids, carboxylic acids, and dicarboxylic acids. Since fermented juice contains more amino acids and less sugar than nectar, it appears that host diet filters the gut flora by favoring microbes that digest compounds abundant in foods. By quantifying the degree to which gut communities vary among host individuals, species and dietary guilds and evaluating how gut microbial composition and catabolic potential are related to host diet, this study highlights the linkages between structure and function in one of the most complex and ubiquitous symbioses in the animal kingdom.

    更新日期:2019-01-22
  • Traditionally managed landscapes do not prevent amphibian decline and the extinction of paedomorphosis
    Ecol. Monogr. (IF 7.698) Pub Date : 2018-12-22
    Mathieu Denoël; G. Francesco Ficetola; Neftali Sillero; Georg Džukić; Miloš L. Kalezić; Tanja Vukov; Irma Muhovic; Vuk Ikovic; Benjamin Lejeune

    Eco‐cultural landscapes are assumed to be favorable environments for the persistence of biodiversity, but global change may affect differently their terrestrial and aquatic components. Few long‐term studies have examined how multiple, global change stressors may affect wetland biodiversity in such environments. Facultative paedomorphosis is a spectacular example of intra‐specific variation, in which biphasic (metamorphosing) amphibians coexist with fully aquatic conspecifics that do not metamorphose (paedomorphs). Paedomorphosis is seriously threatened by global change stressors, but it is unknown to what extent traditional management will allow its long‐term persistence. Here, we tested the effects of alien species introductions while taking into account land use and climate changes on the distribution of two polymorphic newt species (Ichthyosaura alpestris and Lissotriton graecus) in Montenegro by using a 68‐yr data set and Bayesian mixed models integrating complex spatial and temporal structures. We found that, despite the persistence of natural landscapes, metamorphs dramatically declined and paedomorphs were nearly extirpated, losing 99.9% of their aquatic area of occupancy and all the major populations. Fish introduction was the main determinant of decline for both phenotypes. Climate and the presence of crayfish further contributed to the decline of metamorphs, which started later and was less dramatic than that of paedomorphs. The near extinction of paedomorphosis on a country‐wide scale shows how invasive species determine broad‐scale impacts, which can be even stronger than other global change stressors, and underlines the need for immediate management actions to avoid the extinction of a unique developmental process, paedomorphosis.

    更新日期:2019-01-22
  • Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-17
    Winslow D. Hansen; Monica G. Turner

    Robust tree regeneration following high‐severity wildfire is key to the resilience of subalpine and boreal forests, and 21st century climate could initiate abrupt change in forests if postfire temperature and soil moisture become less suitable for tree seedling establishment. Using two widespread conifer species, lodgepole pine (Pinus contorta var. latifolia) and Douglas‐fir (Pseudotsuga menziesii var. glauca), we conducted complementary experiments to ask (1) How will projected early‐ to mid‐21st‐century warming and drying affect postfire tree seedling establishment and mortality? (2) How does early seedling growth differ between species and vary with warming and drying? With a four‐year in situ seed‐planting experiment and a one growing season controlled‐environment experiment, we explored effects of climate on tree seedling establishment, growth, and survival and identified nonlinear responses to temperature and soil moisture. In our field experiment, warmer and drier conditions, consistent with mid‐21st‐century projections, led to a 92% and 76% reduction in establishment of lodgepole pine and Douglas‐fir. Within three years, all seedlings that established under warmer conditions died, as might be expected at lower elevations and lower latitudes of species’ ranges. Seedling establishment and mortality also varied with aspect; approximately 1.7 times more seedlings established on mesic vs. xeric aspects, and fewer seedlings died. In the controlled‐environment experiment, soil temperatures were 2.0°–5.5°C cooler than the field experiment, and warming led to increased tree seedling establishment, as might be expected at upper treeline or higher latitudes. Lodgepole pine grew taller than Douglas‐fir and produced more needles with warming. Douglas‐fir grew longer roots relative to shoots, compared with lodgepole pine, particularly in dry soils. Differences in early growth between species may mediate climate change effects on competitive interactions, successional trajectories, and species distributions. This study demonstrates that climate following high‐severity fire exerts strong control over postfire tree regeneration in subalpine conifer forests. Climate change experiments, such as those reported here, hold great potential for identifying mechanisms that could underpin fundamental ecological change in 21st‐century ecosystems.

    更新日期:2019-01-17
  • Enhancing insights into foraging specialization in the world's largest fish using a multi‐tissue, multi‐isotope approach
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-16
    Alex S.J. Wyatt; Rui Matsumoto; Yoshito Chikaraishi; Yosuke Miyairi; Yusuke Yokoyama; Keiichi Sato; Nao Ohkouchi; Toshi Nagata

    Intra‐species variability in foraging strategies may be common, which has significant implications for efforts to understand and manage enigmatic species like the whale shark Rhincodon typus. The ecological relevance of differences in tissue isotopes within and between individuals in the context of foraging however depends on understanding tissue turnover times and carbon (Δ13C) and nitrogen (Δ15N) discrimination, which can vary with physiology, metabolism, and diet quality. Here, we examine isotope dynamics in captive R. typus as a basis for enhanced ecological insights into wild populations of the world's largest fish and other enigmatic species. A variable diet, principally consisting of two krill (Euphausia pacifica and Euphausia superba) provided an average of 48 ± 20 MJ/d (mean ± SD), or 2.7 ± 1.3 times basal metabolic requirements. On this diet, in agreement with allometric relationships, large body sizes (3,000–4,000 kg) were matched by slow plasma and cartilage turnover rates (empirically derived as 9 months and 3 yr, respectively), which provide tissue‐specific limits on the timescales over which we can isotopically detect diet changes in this species. Average diet‐to‐tissue discrimination showed significant variation between tissues (plasma and cartilage), and among growing and fasting individuals (Δ13C range, 1.5 to 5.5‰; Δ15N range, −0.1 to 2.9‰). Assimilation rates increased with temperature and were higher for the smaller E. pacifica (15 ± 2 mm) than E. superba (48 ± 2 mm). Growth significantly lowered both Δ15Nplasma and Δ15Ncartilage, with inappetence markedly reducing Δ15Nplasma and Δ13Cplasma, as well as significantly altering blood biochemistry. Captive findings facilitated the first robust multi‐tissue growth‐ and nutrition‐corrected isotope analysis of a wild R. typus population, suggesting individual foraging specialization on low trophic level mid‐ocean or coastal prey. Long‐term fasting during ocean‐basin‐scale migrations may be common and such metabolic effects should be carefully quantified when isotopically assessing intra‐species foraging differences. The metabolically constrained multi‐tissue, multi‐isotope approach described can facilitate ecological insights that are indispensable for effective conservation and management of globally threatened, but poorly understood, species by identifying differences in key foraging areas and target prey within and between individuals.

    更新日期:2019-01-17
  • Shifting the conservation paradigm: a synthesis of options for renovating nature under climate change
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-15
    Suzanne M. Prober; Veronica A. J. Doerr; Linda M. Broadhurst; Kristen J. Williams; Fiona Dickson

    Changes in Earth's climate are accelerating, prompting increasing calls to ensure that investments in ecological restoration and nature conservation accommodate such changes. To acknowledge this need, we propose the term “ecological renovation” to describe ecological management and nature conservation actions that actively allow for environmental change. To evaluate and progress the development of ecological renovation and related intervention options in a climate change context, we reviewed the literature and established a typology of options that have been proposed. We explored how these options address emerging principles underpinning climate‐adapted conservation goals and whether the balance of approaches reflected in our typology is likely to be sufficient given expected rapid rates of climate change. Our typology recognizes a matrix of 23 intervention option types arranged on the basis of underpinning ecological mechanisms (“ameliorate changing conditions” or “build adaptive capacity”) on one axis, and the nature of the tools used to manipulate them (“low regrets” or “climate targeted”) on the other. Despite a burgeoning literature since 2008, we found that the majority of effort has consistently focused on low‐regrets adaptation approaches that aim to build adaptive capacity. This is in many ways desirable, but a paradigm shift enabling greater attention to climate‐targeted approaches is likely to be needed as climate change accelerates. When assessed against five emerging principles for setting nature conservation goals in a changing climate, only one option type could deliver to all five, and we identified a conflict between climate‐targeted options and “wildness” values that calls for deeper evaluation. Importantly, much of the inference in the 473 reviewed studies was drawn from ecological reasoning and modeling, with only 16% offering new empirical evidence. We also noted significant biases toward North America and Europe, forest ecosystems, trees, and vertebrates. To address these limitations and help shift the paradigm toward humans as “renovators” rather than “restorers” of a prior world, we propose that ecological researchers contribute by (1) informing societal discourse toward adapting nature conservation goals to climate change, (2) adjusting and upscaling conservation planning to accommodate this suite of climate‐adapted goals, and (3) reconceptualizing experimental approaches to increase empirical evidence and expedite innovation of tools to address change.

    更新日期:2019-01-15
  • Contrasting nitrogen fluxes in African tropical forests of the Congo Basin
    Ecol. Monogr. (IF 7.698) Pub Date : 2019-01-02
    Marijn Bauters; Hans Verbeeck; Tobias Rütting; Matti Barthel; Basile Bazirake Mujinya; Fernando Bamba; Samuel Bodé; Faustin Boyemba; Emmanuel Bulonza; Elin Carlsson; Linnéa Eriksson; Isaac Makelele; Johan Six; Landry Cizungu Ntaboba; Pascal Boeckx

    The observation of high losses of bioavailable nitrogen (N) and N richness in tropical forests is paradoxical with an apparent lack of N input. Hence, the current concept asserts that biological nitrogen fixation (BNF) must be a major N input for tropical forests. However, well‐characterized N cycles are rare and geographically biased; organic N compounds are often neglected and soil gross N cycling is not well quantified. We conducted comprehensive N input and output measurements in four tropical forest types of the Congo Basin with contrasting biotic (mycorrhizal association) and abiotic (lowland–highland) environments. In 12 standardized setups, we monitored N deposition, throughfall, litterfall, leaching, and export during one hydrological year and completed this empirical N budget with nitrous oxide (N2O) flux measurement campaigns in both wet and dry season and in situ gross soil N transformations using 15N‐tracing and numerical modeling. We found that all forests showed a very tight soil N cycle, with gross mineralization to immobilization ratios (M/I) close to 1 and relatively low gross nitrification to mineralization ratios (N/M). This was in line with the observation of dissolved organic nitrogen (DON) dominating N losses for the most abundant, arbuscular mycorrhizal associated, lowland forest type, but in contrast with high losses of dissolved inorganic nitrogen (DIN) in all other forest types. Altogether, our observations show that different forest types in central Africa exhibit N fluxes of contrasting magnitudes and N‐species composition. In contrast to many Neotropical forests, our estimated N budgets of central African forests are imbalanced by a higher N input than output, with organic N contributing significantly to the input‐output balance. This suggests that important other losses that are unaccounted for (e.g., NOx and N2 as well as particulate N) might play a major role in the N cycle of mature African tropical forests.

    更新日期:2019-01-02
  • A multistate open robust design: population dynamics, reproductive effort, and phenology of sea turtles from tagging data
    Ecol. Monogr. (IF 7.698) Pub Date : 2018-08-29
    William L. Kendall; Seth Stapleton; Gary C. White; James I. Richardson; Kristen N. Pearson; Peri Mason

    Understanding population dynamics, and how it is influenced by exogenous and endogenous factors, is important to the study and conservation of species. Moreover, for migratory species, the phenology and duration of use of a given location can also influence population structure and dynamics. For many species, breeding abundance, survival, and reproductive performance, as well as phenology of nesting, are often the most accessible, and therefore, practical elements of their life history to study. For a population of hawksbill sea turtles (Eretmochelys imbricata), we modeled population change for nesters and total adult females, survival, and breeding probability, from 25 yr of intensive tagging data. We modeled breeding probability as a function of the number of years since last breeding and tested for differences between neophyte and experienced nesters. For each year, we also estimated the number of clutches deposited per female, and phenology of use, for neophytes and experienced nesters. To implement the analysis, we developed a novel generalized multistate open robust design mark–recapture modeling framework, with parameters for survival and transition probabilities, and for each primary period, state structure and arrival, persistence, and detection probabilities. Derived parameters included abundance of observable and unobservable components of the population, residence time, expected arrival and departure periods, and per‐period intensity of study area use. Abundance of nesters increased over most of the time series. Survival probability was 0.935 ± 0.01 (estimate ± SE). Virtually all hawksbills skipped at least one year of nesting. Breeding probability increased by skipping a second year, but then decreased thereafter. Subsequent breeding probability was lower for neophyte nesters than for experienced nesters, but the effect was weaker than the effect of years since breeding. Clutch frequency varied by year, with no discernable pattern of differences between neophytes and experienced nesters. Mean arrival and departure dates also varied, with a slight shift of nesting activity to earlier in the season. The multistate open robust design model developed here provides a flexible framework for modeling the dynamics of structured migratory populations and the phenology and duration of their seasonal use of study areas.

    更新日期:2018-11-29
  • Mechanisms influencing the coexistence of multiple consumers and multiple resources: resource and apparent competition
    Ecol. Monogr. (IF 7.698) Pub Date : 2018-08-27
    Mark A. McPeek

    Interactions among multiple resources and consumers involve two indirect interactions: resource competition among consumers and apparent competition among resources. However, competition among multiple consumers is typically viewed through the lens of direct interactions embodied in the Lotka‐Volterra competition model, which fails to capture the mechanisms of these indirect interactions. In this paper, I analyze various elaborations of MacArthur's and Tilman's original consumer–resource models including more than two species per trophic level, saturating functional responses, and direct intraspecific density dependence within the consumers. First, the simplest model with two resources and two consumers with linear functional responses is analyzed via the structure of the resulting isoclines, and this is reconciled with Tilman's graphical ZNGI/consumption vector approach. With three species at each trophic level even in this simple model, each consumer is not required to have the largest impact on the resource that most limits its growth for multiple consumers to coexist. In fact, a consumer that is an inferior competitor on each resource in isolation may still coexist with superior competitors, and conversely a consumer that is an inferior competitor on each available resource may still be able to drive all other consumers extinct. However, the maximum number of coexisting consumers is set by the number of available resources. Saturating functional responses do not qualitatively alter the conditions for multiple consumers and resources to coexist at a stable point equilibrium but do increase the range of apparent competitive abilities for resources that can invade and coexist. Saturating functional responses also increase the range of dynamics that the community may display (i.e., limit cycles and chaos), which previous analyses have shown can permit more consumer species than resources to coexist. Adding direct intraspecific density dependence in the consumers, either in the form of feeding interference or density‐dependent demographic rates, permit more consumers to coexist than available resources, even at stable point equilibria. Understanding the indirect effects that cascade through a community is essential to predicting community changes and understanding how species at multiple trophic levels coexist, and these indirect effects should not be shrouded behind the curtain of Lotka‐Volterra competition.

    更新日期:2018-11-29
  • Complex long‐term dynamics of pollinator abundance in undisturbed Mediterranean montane habitats over two decades
    Ecol. Monogr. (IF 7.698) Pub Date : 2018-11-20
    Carlos M. Herrera

    Current notions of “pollinator decline” and “pollination crisis” mainly arose from studies on pollinators of economic value in anthropogenic ecosystems of mid‐latitude temperate regions. Comprehensive long‐term pollinator data from biologically diverse, undisturbed communities are needed to evaluate the actual extent of the so‐called “global pollination crisis.” This paper analyzes the long‐term dynamics of pollinator abundance in undisturbed Mediterranean montane habitats using pollinator visitation data for 65 plant species collected over two decades. Objectives are (1) to elucidate patterns of long‐term changes in pollinator abundance from the perspectives of individual plant species, major pollinator groups, and the whole plant community and (2) to propose a novel methodological implementation based on combining a planned missing data design with the analytical strength of mixed effects models, which allows one to draw community‐wide inferences on long‐term pollinator trends in species‐rich natural habitats. Probabilistic measurements (“patch visitation probability” and “flower visitation probability” per time unit) were used to assess pollinator functional abundance for each plant species on two separate, randomly chosen years. A total of 13,054 pollinator censuses accounting for a total watching effort of 2,877,039 flower‐min were carried out on 299 different dates. Supra‐annual unstability in pollinator functional abundance was the rule, with visitation probability to flowering patches and/or individual flowers exhibiting significant heterogeneity between years in the majority of plant species (83%). At the plant‐community level, there was a significant linear increase in pollinator functional abundance over the study period. Probability of pollinator visitation to flowering patches and individual flowers increased due to increasing visitation by small solitary bees and, to a lesser extent, small beetles. Visitation to different plant species exhibited contrasting changes, and insect orders and genera differed widely in sign and magnitude of linear abundance trends, thus exemplifying the complex dynamics of community‐wide changes in pollinator functional abundance. Results of this investigation indicate that pollinator declines are not universal beyond anthropogenic ecosystems; stress the need for considering broader ecological scenarios and comprehensive samples of plants and pollinators; and illustrate the crucial importance of combining ambitious sampling designs with powerful analytical schemes to draw reliable inferences on pollinator trends at the plant community level.

    更新日期:2018-11-21
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