Environmental filtering and spillover explain multi-species edge responses across agricultural boundaries in a biosphere reserve

J Van Schalkwyk,M J Samways,R Gaigher,J S Pryke

doi:10.1038/s41598-020-71724-1

Abstract

To ensure integrity of protected areas we need to understand how species respond to anthropogenic borders. We investigate, from a metacommunity perspective, the direct and indirect mechanisms by which transformed areas affect distribution patterns of ground-living arthropod assemblages inhabiting an extensive protected area adjacent to fruit orchards in an important biosphere reserve. Arthropods and environmental variables were sampled along transects perpendicular to natural-orchard edges. Influence of distance from orchard boundary, degree of impermeability of the boundary, orchard habitat quality (local scale land-use intensity), and edge-induced changes in local environmental variables on arthropod species richness and composition in non-crop habitats were assessed. Arthropod groups were assessed in terms of habitat fidelity: species associated with natural habitat (stenotopic species), those within crop habitat (cultural species), and those showing no preference for either habitat (ubiquitous species). Spillover resulted in higher cultural species richness near edges, but not higher overall species richness. Environmental filtering was important for stenotopic species composition, which was influenced by edge-induced changes in environmental variables. Ubiquitous species composition was determined by orchard impermeability. Increased orchard habitat quality was associated with higher cultural and ubiquitous species richness. The effects of orchards on assemblages in natural habitats can be variable, but predictable when using species habitat specificity in conjunction with a metacommunity framework. High intensity orchards may act as sink habitats, especially for species that readily disperse between crop and natural habitats. Here we recommend that local buffer strips are > 85 m wide, which will reduce the influence of cultural species spillover on sensitive natural ecosystems.

Highlights

To ensure integrity of protected areas we need to understand how species respond to anthropogenic borders
Results from Generalized linear mixed-effects models (GLMMs) showed that edge-associated change in local environmental variables was important for all species and ubiquitous species richness (Table 2, Fig. 2a and Figure S1)
Edge-associated change in local conditions was negatively correlated with distance-to-edge, and higher species richness was associated with changes in local environmental conditions close to the orchard edge

Summary

Introduction

To ensure integrity of protected areas we need to understand how species respond to anthropogenic borders. Influence of distance from orchard boundary, degree of impermeability of the boundary, orchard habitat quality (local scale land-use intensity), and edge-induced changes in local environmental variables on arthropod species richness and composition in non-crop habitats were assessed. The United Nations Education, Scientific and Cultural Organization’s (UNESCOs) Man and the Biosphere Programme is considered one of the better options for integrating conservation with surrounding landscapes, as it recognizes that landscapes can be transformed along a gradient of land-use intensity In this regard, Biosphere Reserve (BR) buffer and transition zones are key functional spaces that represent the interface between conservation and resource extraction. Influences biotope structure[12,13,14], and unique species composition at edges can result from the blending of juxtaposed environmental c onditions[15] These three main effects do not operate in isolation. A species’ degree of habitat specificity can determine if and for how long it is exposed to management practices in transformed a reas[20,21]

Methods

Results

Conclusion