Habitat heterogeneity is correlated with isotopic niche breadth across the range of a mammalian generalist mesopredator

Abstract

Although generalists are becoming increasingly abundant and widespread, little is known about their response to ecological variation they encounter across their range. For example, the generalist’s flexible diet is cited to help explain recent range expansions, but no study has directly examined this claim. Here, we use stable isotope values of the Virginia opossum (Didelphis virginiana), a true generalist, to examine an extension of MacArthur’s habitat heterogeneity hypothesis for a single generalist species. If a generalist’s diet reflects local food abundance, then more heterogeneous landscapes should result in broader niches. We used stable isotope analysis, landcover indices, and WordClim data to further evaluate how the opossum’s use of its environment varies across ancestral regions, expansion fronts, and regions of human-facilitated introductions. Niche breadth varied across its range, especially between expansion fronts. We found a positive relationship between landcover diversity and isotopic niche breadth. WorldClim variables linked to aridity and C4 plant abundance were most strongly associated with nitrogen (δ15N) and carbon (δ13C) values, respectively. Our results reveal that a generalist’s stable isotope signature reflects its local environment, demonstrating their flexible diet is captured with stable isotopes and supporting the “generalist habitat heterogeneity hypothesis.”