Species range contractions in geographic and environmental space.

Abstract

Species range contractions are a defining feature of the Anthropocene. Given their prevalence, a key question arises: do range contractions follow consistent patterns? Empirical studies have produced mixed results, revealing some emergent patterns, but also considerable variation among taxa. Here, we present a framework that seeks to explain this variation, conceptualising range contractions as the outcome of the interplay between species' intrinsic population growth rates and the impact of threats across environmental gradients. Our framework shows how four primary patterns of range contraction arise, with a fifth emerging under incomplete threat spread. By describing when, where, and why particular patterns of decline occur, our framework advances understanding of species' responses to global change and provides a basis for more generalisable conservation strategies.