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Structure and functional composition of macroinvertebrate communities in coastal plain streams across a precipitation gradient
Freshwater Biology ( IF 2.7 ) Pub Date : 2022-07-26 , DOI: 10.1111/fwb.13968
Fernando R. Carvallo 1 , Bradley A. Strickland 2 , Sean K. Kinard 2 , Brandi Kiel Reese 3, 4 , James Derek Hogan 1 , Christopher J. Patrick 2
Affiliation  

1 INTRODUCTION

Average global temperature has exponentially increased since the industrial revolution from 0.8 to 1.2°C, causing significant changes in the frequency, intensity, and predictability of weather events now and in the future (IPCC, 2018). For instance, premature spring snow melts, increased forest fires, and increases in aridity have been documented across the globe (Seager et al., 2007; Ummenhofer & Meehl, 2017). Simultaneously, the variation in the frequency, intensity, and timing of rainfall events has become less spatially and seasonally predictable (Andrys et al., 2017; Szwed, 2019). These changes are also impacting stream ecosystems globally. For example, there have been regional changes in stream intermittency across the U.S.A. (Zipper et al., 2021) and decreased water flows and water security in Nepal (Dahal et al., 2018).

Rainfall, which drives the hydrological cycle, is a key factor shaping stream ecosystems (Lytle & Poff, 2004; Mims & Olden, 2012). Many studies have shown that macroinvertebrate community dynamics are driven by hydrological flow disturbance regimes, which is largely controlled by precipitation (Dodds et al., 2019; Lake, 2003, 2005; Mathers et al., 2019; Poff & Ward, 1989). However, forecasting specific effects of changes to precipitation patterns on stream ecosystems is challenging because unlike studies on temperature effects (Arai et al., 2015; Burgmer et al., 2006; Domisch et al., 2011; Hering et al., 2009), studies isolating rainfall effects are underrepresented in the literature (Adámek et al., 2016; Reynolds et al., 2015). What is known about how rainfall affects the structure and function of stream ecosystems comes primarily from large-scale observational studies conducted across climate gradients (e.g., Bonada et al., 2007). These studies show that arid systems receiving little annual precipitation generally lack canopy cover from riparian zone trees, leading to high solar insolation and low allochthonous input, and thus depend primarily upon autochthonous carbon from primary productivity (Benfield, 1997; Pomeroy et al., 2000). Arid stream hydrological regimes are typically flashy, with punctuated periods of dry riverbed and high energy flash floods—a common but stochastic occurrence (Jackson & Fisher, 1986). In response to these flow disturbances, arid streams tend to contain low species richness (Sheldon et al., 2002) and biomass production is stochastic through space and time, at times exceeding the secondary production of mesic (humid) systems by an order of magnitude (Grimm & Fisher, 1989; Lamberti & Steinman, 1997). The communities of arid streams have been observed to be inhabited predominantly by taxa that are better adapted for recolonisation after hydrological disturbance through faster generation time, wider dispersal ability, and greater fecundity than the taxa in the more hydrologically stable wetter systems (Bonada et al., 2007; Mellado-Díaz et al., 2007). The predominance of algae caused by high insolation also drives a higher proportion of taxa adapted for scraping and grazing algae than in wetter streams (Benfield, 1997; Grafius, 1974; Tait, 1997).

In contrast, wetter (mesic) streams are characterised by dense canopy cover provided by trees in the riparian zone. The trees decrease insolation, decreasing primary productivity, and increase allochthonous carbon input into the streams (Benfield, 1997). Due to predictable rainfall patterns and the role of terrestrial vegetation in moderating the hydrological cycle, mesic systems typically have much more stable hydrological regimes, more stable baseflow conditions and floods with more gentle rising and falling limbs occurring at predictable periods within the year (Dodds et al., 2015; Mellado-Díaz et al., 2007). These predictable and stable conditions in mesic streams can increase the success of species that depend on distinct niches in time that correspond with their life history strategies, supporting higher temporal β-diversity and more temporally stable biomass production rates than the arid streams through an increase in species turnover between seasons (Konar et al., 2013; Tonkin et al., 2017). Mesic streams in low-disturbance drainages are often inhabited by communities consisting of more specialised competitive species than rapidly colonising species (Boulton et al., 1992).

Precipitation regime determines hydrological conditions, particularly frequency of disturbance, and the identity of basal resources, which drive differences between arid and mesic stream ecosystem structure and function. For instance, a recent global meta-analysis showed that frequency of low flow disturbance events was the most important predictor of riverine benthic invertebrate secondary production after water temperature (Patrick et al., 2019). However, a challenge with interpreting the causal nature behind these patterns is the breadth of environmental variation when comparing systems across ecoregions. Observational studies that derive process from pattern (see Dodds et al., 2015) rely on a space for time substitution, but interpretations from these data are limited due to confounding environmental variables such as elevation, air temperature, and sun angle that are unavoidable in large latitudinal studies (Fukami & Wardle, 2005). To independently evaluate the effects of rainfall on stream structure and function, a study region needs to span a rainfall gradient with minimal variation in other factors (Fukami & Wardle, 2005; Liu & Schwartz, 2012).

Fortunately, the Texas Gulf Coastal Prairie (TGCP) is exactly such a region. Along the central TGCP, mean annual rainfall increases from 550 mm (semi-arid) to 1,350 mm/year (sub-humid) at a rate of 2.3 mm annual rainfall per km, making it the steepest non-montane rainfall gradient in the continental U.S.A. Along the gradient there are minimal covarying changes in underlying geology, elevation, and air temperature. Here, we report on 14 months of monthly sampling of invertebrate communities and associated environmental variables in nine streams distributed along the TGCP rainfall gradient. Our objective was to investigate how the composition, abundance, and diversity of stream invertebrate communities changed in response to interacting temporally proximate flow conditions, degrees of seasonality, and historical precipitation regimes.

Evidence suggests that greater predictability in flow regime increases temporal diversity through more specialist consumers occupying more temporally available niches and causing high temporal turnover in community composition (Tonkin et al., 2017). Thus, we predict that the abundance and diversity of invertebrates will increase with annual precipitation because wetter streams would have higher hydrological stability and seasonal predictability, supporting greater temporal diversity (Sheldon et al., 2002; Tonkin et al., 2017). This same mechanism should also drive greater seasonal shifts in invertebrate abundance and community composition in wetter sites. In contrast to the wetter streams, we predict that semi-arid sites would show stochastic temporal patterns of abundance and community composition driven by high and low flow events. We also expect semi-arid stream invertebrate communities to have greater proportions of taxa with functional adaptations to drought and flash flood disturbances including resistance to desiccation, ability to exit the water, multivoltinism, high dispersal potential, and high population turnover.



中文翻译:

跨降水梯度的沿海平原溪流大型无脊椎动物群落的结构和功能组成

1 简介

自工业革命以来,全球平均气温呈指数级上升,从 0.8°C 上升到 1.2°C,导致现在和未来天气事件的频率、强度和可预测性发生显着变化(IPCC,  2018 年)。例如,全球范围内记录了过早的春季融雪、森林火灾增加和干旱加剧(Seager 等人,  2007 年;Ummenhofer 和 Meehl,  2017 年)。同时,降雨事件的频率、强度和时间的变化在空间和季节上变得难以预测(Andrys et al.,  2017 ; Szwed,  2019)。这些变化也在影响全球的河流生态系统。例如,美国的河流间歇性发生了区域性变化(Zipper 等人,  2021 年),尼泊尔的水流量和水安全性下降(Dahal 等人,  2018 年)。

驱动水文循环的降雨是塑造河流生态系统的关键因素(Lytle & Poff,  2004 ; Mims & Olden,  2012)。许多研究表明,大型无脊椎动物群落动态是由水文流动扰动机制驱动的,这在很大程度上受降水控制(Dodds et al.,  2019 ; Lake,  2003 , 2005 ; Mathers et al.,  2019 ; Poff & Ward,  1989)。然而,预测降水模式变化对河流生态系统的具体影响具有挑战性,因为与温度效应研究不同(Arai 等人,  2015 年;Burgmer 等人,  2006 年;Domisch 等人,  2011 年); Hering 等人,  2009 年),孤立降雨效应的研究在文献中的代表性不足(Adámek 等人,  2016 年;雷诺兹等人,  2015 年)。关于降雨如何影响河流生态系统的结构和功能的已知信息主要来自跨气候梯度进行的大规模观测研究(例如,Bonada 等人,  2007 年)。这些研 _)。干旱河流水文状况通常是短暂的,断断续续地出现干涸的河床和高能山洪——这是一种常见但随机的事件(Jackson & Fisher,  1986 年)。为应对这些流动干扰,干旱河流的物种丰富度往往较低(Sheldon 等人,  2002 年),并且生物量生产在空间和时间上是随机的,有时超过中等(潮湿)系统的二次生产一个数量级(格林和费舍尔,  1989 年;兰伯蒂和斯坦曼,  1997 年)。已经观察到干旱河流群落主要居住在类群中,这些类群比水文更稳定的湿润系统中的类群更适合在水文扰动后通过更快的世代时间、更广泛的分散能力和更大的繁殖力重新定殖(Bonada et al. ,  2007 年;Mellado-Díaz 等人,  2007 年)。由高日照引起的藻类占优势也推动了比在更潮湿的溪流中适应刮擦和放牧藻类的类群比例更高(Benfield,  1997;Grafius,  1974;Tait,  1997)。

相比之下,较湿润(中等)溪流的特点是河岸带树木提供的茂密树冠覆盖。树木减少了日照,降低了初级生产力,并增加了流入河流的外来碳(Benfield,  1997 年)。由于可预测的降雨模式和陆地植被在调节水文循环中的作用,中枢系统通常具有更稳定的水文状况、更稳定的基流条件和洪水,在一年内可预测的时期发生更平缓的上升和下降分支(Dodds 等等人,  2015 年;Mellado-Díaz 等人,  2007 年)。中干流中的这些可预测和稳定的条件可以增加物种的成功,这些物种在时间上依赖于与其生活史策略相对应的不同生态位,通过增加季节之间的物种更替(Konar 等人,  2013 年;Tonkin 等人,  2017 年)。低干扰排水系统中的中央溪流通常居住在由更专业的竞争物种组成的群落中,而不是快速定殖的物种(Boulton 等,  1992)。

降水状况决定了水文条件,特别是扰动频率,以及基础资源的特性,这些决定了干旱和中水河流生态系统结构和功能之间的差异。例如,最近的一项全球荟萃分析表明,低流量扰动事件的频率是水温之后河流底栖无脊椎动物二次生产的最重要预测因素(Patrick 等人,  2019 年)。然而,在比较跨生态区域的系统时,解释这些模式背后的因果性质的挑战是环境变化的广度。从模式衍生过程的观察性研究(参见 Dodds 等人,  2015) 依赖于时间替换的空间,但由于在大型纬度研究中不可避免的环境变量(例如海拔、气温和太阳角度)混杂(Fukami 和 Wardle,  2005 年),因此对这些数据的解释是有限的。为了独立评估降雨对河流结构和功能的影响,研究区域需要跨越降雨梯度,而其他因素的变化最小(Fukami & Wardle,  2005 ; Liu & Schwartz,  2012)。

幸运的是,德克萨斯湾沿岸草原 (TGCP) 正是这样一个地区。沿着 TGCP 中部,年平均降雨量从 550 毫米(半干旱)增加到 1,350 毫米/年(半湿润),年降雨量为每公里 2.3 毫米,使其成为大陆最陡的非山地降雨梯度美国 沿着梯度,底层地质、海拔和气温的共变变化很小。在这里,我们报告了沿 TGCP 降雨梯度分布的九条溪流中无脊椎动物群落和相关环境变量的每月采样 14 个月。我们的目标是调查河流无脊椎动物群落的组成、丰度和多样性如何随着时间上接近的流动条件、季节性程度和历史降水制度的相互作用而变化。

有证据表明,流动状态的更大可预测性通过更多专业消费者占据更多时间可用的生态位并导致社区组成的高时间周转来增加时间多样性(Tonkin et al.,  2017)。因此,我们预测无脊椎动物的丰度和多样性将随着年降水量的增加而增加,因为较湿润的溪流将具有更高的水文稳定性和季节可预测性,从而支持更大的时间多样性(Sheldon et al.,  2002 ; Tonkin et al.,  2017)。同样的机制也应该推动更潮湿地区无脊椎动物丰度和群落组成的更大季节性变化。与较湿的溪流相比,我们预测半干旱地点将显示出由高流量和低流量事件驱动的丰度和群落组成的随机时间模式。我们还预计半干旱河流无脊椎动物群落具有更大比例的分类群,这些分类群具有对干旱和山洪干扰的功能适应性,包括抗干燥性、离开水的能力、多伏性、高扩散潜力和高人口流动率。

更新日期:2022-07-26
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