Land-cover gradients determine alternate drivers of mammalian species richness in fragmented landscapes

Abstract

Abstract Context Understanding habitat fragmentation is a critical concern for nature conservation and the focus of intense debate in landscape ecology. Resolving the uncertainty around the effects of habitat fragmentation on biodiversity remains an ongoing challenge that requires the successful delineation of multiple patch-landscape interactions. Objectives We carried out a regional analysis on species richness of woodland mammals to determine the relative influence of structural, compositional and functional characteristics related to woodland habitat across different land-cover gradients. Methods We calculated the Edge-weighted Habitat Index, an area-weighted measure of functional connectivity that incorporates a mechanistic estimate of edge-effects, for interior woodland habitat. We compared its influence on mammalian species richness to that of increasing edge and patch density, landscape diversity, and a habitat-only model, in different contexts of matrix hostility across Northern England in the UK. Results Our results demonstrate the relevance of alternative drivers of species richness resulting from patch-landscape interactions across gradients of matrix hostility. Evidence is provided for positive and negative effects of increasing structural (edge density), functional (connected interior habitat) and compositional (landscape diversity) attributes, varying according to matrix type and intensity. Results were sensitive to dominant land-cover types in the matrix and the scale of observation. Conclusion This study provides new insights into fragmentation effects on biodiversity and clarifies assumptions around the relative influence of structural, compositional and functional habitat characteristics on landscape-level species richness. We highlight the presence of thresholds, related to matrix hostility, that determine alternative drivers of species richness in woodland mammals. These drivers, and related thresholds, were sensitive to the scale of observation and landscape context. Landscape decisions aimed at promoting biodiversity should consider sources of matrix hostility and homogeneity at scales relevant to ecological processes of interest.