Structural heterogeneity affects raptor assemblages and niche characteristics in mixed‐grass ecosystems

Abstract

AbstractLandscape function is largely determined by landscape structure. Evidence suggests that landscape heterogeneity often benefits generalists over sympatric specialists. The scale at which animals perceive that heterogeneity likely varies across species and could play an important role in determining the species assemblages supported by different landscapes. In this study, we investigated the relative importance of landscape heterogeneity in the structuring of raptor assemblages in mixed‐grass prairie. We compared niche breadth and overlap of 14 species in two landscapes that differed in heterogeneity. We used a modified line transect approach and distance sampling to determine approximate locations of raptors and mapped these locations in a GIS. We then compared land cover in buffered areas around detection locations to randomly selected locations at different scales. We calculated Outlying Mean Index to quantify niche breadth and compare among species. Species composition was similar in both landscapes, but niche characteristics differed according to heterogeneity. Raptor assemblages were better predicted by land cover composition in heterogeneous landscapes than by land cover configuration in homogenous landscapes. Outlying Mean Index analysis suggested that six of the 14 species occupied marginal niches and narrower niche breadths in homogeneous landscapes. None of these species demonstrated marginality but occupied broader niche breadths in heterogeneous landscapes. Our study provides evidence that heterogeneity is important in providing conditions necessary to support multiple, sympatric birds of prey in mixed‐grass prairie. Species overlapped broadly under heterogeneity but less in landscapes with larger patches of distinct land cover types.