Environmental “Wiggles” as Stabilizers of Species Range Limits Set by Interspecific Competition

Abstract Whether interspecific competition is a major contributing factor in setting species’ range limits has been debated for a long time. Evolutionary models have helped propose a possible mechanism: interspecific competition interacts with the disruptive effects of gene flow along an environmental gradient to halt range expansion of species when they meet and compete with each other. However, the stability of such range limits has not previously been well-addressed. Here we use a deterministic evolutionary model to show that, when the environmental gradient varies linearly in space, range limits set by interspecific competition are unlikely to be evolutionarily stable. However, we demonstrate that step-like nonlinearities in the environmental optimum for a fitness-related phenotypic trait, or sharp changes in the steepness of the trait optimum, can stabilize competitively-formed range limits. We show that the stability of the range limits established at such nonlinearities is sufficiently robust against environmental perturbations such as climate change. We note that strong climatic changes can still destabilize the range limits, depending on how the relative dominance of the species changes across the environmental nonlinearities. Therefore, our results further highlight the importance of measuring the competitive ability of species when predicting their response to climate change.