Forest cover and heterogeneous pastures shape the diversity of predatory rove beetles in tropical riparian habitats

Highlights

• Riparian vegetation harbored 27% exclusive rove beetle species and 61% of total abundance.

• Rove beetle diversity was greater in heterogeneous pastures and micro-basins with <40% of forest cover.

• Heterogeneous pastures and riparian vegetation support complementary rove beetle assemblages.

• Abundance decline of riparian species seems to allow rare species to colonize heterogeneous pastures.

Abstract

In tropical landscapes, forest remnants have been reduced to narrow strips of vegetation along rivers and streams surrounded by agricultural land that affects biodiversity, depending on the habitat and landscape characteristics. To assess the effect of riparian forest loss on the diversity of Staphylininae predatory rove beetles, we considered two habitat conditions (river sites with riparian vegetation and sites with heterogeneous pastures) within two micro-basin types (with >70% and <40% forest cover) in a tropical montane cloud forest landscape, Mexico. Beetles were collected using baited pitfall traps during the rainy season of 2014. No differences were found between micro-basin types and, although species richness (⁰D) was similar between habitat conditions, when the diversity of common (¹D) and dominant (²D) species was considered, sites with heterogeneous pastures were almost twice as diverse as those with riparian vegetation. All diversity measurements were greater in sites with heterogeneous pastures of either micro-basin type. Air temperature and canopy cover were the environmental variables that best explained the variation in beetle species composition. The greatest environmental differences related to species composition were detected between habitat conditions and were more evident in sites with heterogeneous pastures and low forest cover in the surroundings. The results suggest that replacing riparian vegetation with heterogeneous pastures, within micro-basins that lost between 30% and 60% of their forest cover, does not significantly reduce the diversity of predatory rove beetle but rather modifies the beetle composition. Effective formulation of management strategies to mitigate the impact of land use modification therefore requires an understanding of the interaction between vegetation remnants and landscape characteristics.

Introduction

In human–dominated landscapes, riparian vegetation acts as a reservoir for many terrestrial taxa and often differs in species composition from neighboring forests or other land use types, increasing regional diversity (Naiman, Decamps & Pollock, 1993; Sabo et al., 2005). At the landscape scale, vegetation associated with watercourses provides habitat and resources for feeding and reproduction in a large number of species (Fahrig et al., 2011; Ries, Fletcher, Battin & Sisk, 2004). Species diversity associated with riparian zones is therefore expected to be influenced both by habitat structural characteristics (e.g., canopy and leaf litter cover) and the surrounding landscape (e.g., land cover types, forest edge density) (Braun, Pires, Stenert, Maltchik & Kotzian, 2018; Marczak et al., 2010).

Riparian zones are complex ecosystems that link water and land environments and provide multiple ecological services such as habitat connectivity and maintenance of biodiversity, riverbank reinforcement, pollution mitigation, nutrient redistribution and delivery and amenity and recreation, all of which are of great value to basin functioning and human well-being (Naiman et al., 1993, Richardson et al., 2007). For these reason, riparian vegetation remnants are an important ecosystem for conservation planning in order to promote structural and functional landscape connectivity to guarantee both the persistence of species and integrity of ecological functions (Rudnick et al., 2012).

The presence and spatial configuration of native vegetation and other land uses such as crops and pastures are among the most important factors that influence species diversity in agricultural landscapes (Fahrig et al., 2011). Intense, but localized, human activity increases landscape heterogeneity, promoting higher species diversity at the local and regional level (Tscharntke et al., 2008). In contrast, landscape homogenization due to the dominance of certain land uses (e.g., treeless pastures) often brings negative impacts on species diversity (Fahrig et al., 2011; Watling, Nowakowski, Donnelly & Orrock, 2011). However, to understand the contribution made by habitat remnants such as riparian vegetation to biodiversity conservation, it is necessary to evaluate their interaction with the surrounding landscape characteristics, which requires studies that consider different spatio-temporal scales (Tscharntke et al., 2012).

Rove beetles (Staphylinidae) make up an important but little-known element of biodiversity in most terrestrial ecosystems, with approximately 65 thousand species described (Irmler & Lipkow, 2018). Necrophilous rove beetles are generalist predators associated with carrion, and some species are associated with specific habitat conditions (Dekeirsschieter, Frederick, Verheggen, Drugmand & Haubruge, 2013; Mądra, Konwerski & Matuszewski, 2014). Rove beetles represent a significant proportion of the predator insect fauna in riparian vegetation (Gutiérrez-Chacon, Zuñiga, Van Bodegom, Chara & Giraldo, 2009). In these environments, Staphylinidae predators have a diet comprised mainly of aquatic invertebrates (some species up 80%) and are therefore considered an important functional component of riverine systems by contributing to the transfer of biomass from aquatic systems to terrestrial food webs (Eyre, Lott & Luff, 2001; Paetzold, Schubert & Tockner, 2005, 2008). The diversity patterns of rove beetles have mainly been explained by microenvironmental conditions and habitat structure (Caballero, León-Cortés & Morón-Ríos, 2009; Irmler & Gürlich, 2007; Irmler & Lipkow, 2018), and a few studies have focused on evaluating the role played by the surrounding landscape supporting the diversity of this insect group (Dauber et al., 2005; Rusch, Birkhofer, Bommarco, Smith & Ekbom, 2014).

In this study, we examined how the diversity and species composition of predatory rove beetles vary in a tropical montane cloud forest (TMCF) landscape in central Veracruz, Mexico, with respect to: i) forest cover at the micro-basin scale (micro-basins dominated by forest and micro-basins dominated by pastures), ii) habitat condition (sites with native riparian vegetation and sites with heterogeneous pastures) and iii) habitat condition as a function of micro basin type. In addition, we determined which site and microsite environmental variables explained species composition. We tested the hypothesis that modification of the environmental conditions (e.g., microclimate and availability of microhabitats), due to the replacement of native riparian vegetation with cattle pastures, will reduce rove beetle diversity, and we expect this reduction to become more evident as the area of TMCF decreases at the micro-basin scale.