Using species co‐occurrence patterns to quantify relative habitat breadth in terrestrial vertebrates

Abstract

The breadth of habitats that a species uses may determine its vulnerability to environmental change, with habitat specialists at greater risk than generalists. To test that hypothesis, we need a valid index of habitat specialization. Existing indices require extensive data, or ignore the magnitude of differences among habitat categories. We suggest an index based on patterns of species co‐occurrence within each of the 101 habitat categories recognized by the International Union for Conservation of Nature. Using this metric, a species is allocated a quantitative score based on the diversity of other taxa with which it co‐occurs: a generalist species occurs in a range of habitat categories that vary considerably in species composition, whereas a specialist species is found only in habitats that contain a consistent suite of other species. We provide data on these scores for 22,230 vertebrate species and show that habitat breadth varies among Classes (amphibians > birds > mammals > reptiles). Within each Class, generalist species are less likely to be in decline or threatened with extinction. Because our index is continuous, based on biologically relevant parameters, and easily calculated for a vast number of taxa, its use will facilitate analyses of the evolution and consequences of habitat specialization.