On the sympatric evolution and evolutionary stability of coexistence by relative nonlinearity of competition
Abstract
If two species exhibit different nonlinear responses to a single shared resource, and if each species modifies the resource dynamics such that this favors its competitor, they may stably coexist. This coexistence mechanism, known as relative nonlinearity of competition, is well understood theoretically, but less is known about its evolutionary properties and its prevalence in real communities. We address this challenge by using adaptive dynamics theory and individual-based simulations to compare community stabilization and evolutionary stability of species that coexist by relative nonlinearity. In our analysis, evolution operates on the species’ density-compensation strategies, and we consider a trade-off between population growth rates at high and low resource availability. We confirm previous findings that, irrespective of the particular model of density dependence, there are many combinations of overcompensating and undercompensating density-compensation strategies that allow stable coexistence by relative nonlinearity. However, our analysis also shows that most of these strategy combinations are not evolutionarily stable and will be outcompeted by an intermediate density-compensation strategy. Only very specific trade-offs lead to evolutionarily stable coexistence by relative nonlinearity. As we find no reason why these particular trade-offs should be common in nature, we conclude that the sympatric evolution and evolutionary stability of relative nonlinearity, while possible in principle, seems rather unlikely. Our study highlights the need for combining ecological and evolutionary perspectives for gaining a better understanding of community assembly and biogeographic patterns.
What the paper shows and why it matters (AI-generated)
Two species can stably coexist on a single shared resource if they respond to it nonlinearly in different, mutually favourable ways — a mechanism well understood in ecological theory but rarely examined for whether it could actually evolve and remain evolutionarily stable. Using adaptive dynamics and individual-based simulations, the authors find that while many density-compensation strategy combinations permit this coexistence in principle, only very specific trade-offs are evolutionarily stable against invasion by an intermediate strategy — grounds for scepticism that the mechanism, though mathematically real, is common in nature. The result has stayed a reference point for later work combining ecological and evolutionary perspectives on coexistence, including the authors' own subsequent review of mechanistic simulation models.