Coexistence theory provides the key to integrating species interactions into predictions of species’ range limits
A fundamental goal of ecology is to predict where species will be present (i.e. their geographic distribution). It is currently unclear when species’ distributions depend on species interactions. Small-scale studies suggest that interactions among species, such as competition, are important. It is less clear when these interactions matter at large spatial scales; we rarely have the opportunity to experimentally examine the large-scale consequences of species’ interactions.
Here we argue that coexistence theory provides powerful, underexploited tools to resolve the effect of competition on species’ distributions. Coexistence theory seeks to identify conditions where competing species can be present at a given location. As a result, an understanding of when competing species coexist can provide an understanding of when one species influences the presence of another. Conditions that promote coexistence reduce the effect of competition on species’ distributions. Experiments designed to study coexistence can be modified to anticipate the effect of competition on range limits. Results from coexistence theory can be used to link a range of competitive interactions to their effects on species’ distributions. Finally, we discuss how these results can be used to improve predictions of changes in species’ distributions.