On the sympatric evolution of coexistence by relative nonlinearity of competition
Florian Hartig, Tamara Münkemüller, Karin Johst, Ulf Dieckmann
(Submitted on 14 Aug 2013)

If two species show different nonlinear responses to a single shared resource, and if each species modifies resource dynamics such that it favors its competitor, they may stably coexist. While the mechanism behind this phenomenon, known as relative nonlinearity of competition, is well understood, less is known about its evolutionary properties and its prevalence in real communities. We address this challenge by using the adaptive dynamics framework as well as individual-based simulations to compare dynamic and evolutionary stability of communities coexisting through relative nonlinearity. Evolution operates on the species’ density compensation strategies, and a trade-off between growth at high versus low resource availability (population density) is assumed. We confirm previous findings that, irrespective of the particular model of density-dependence, there are usually broad ranges of coexistence between overcompensating and undercompensating density-compensation strategies. We show that most of these strategies, however, are not evolutionarily stable and will be outcompeted by a single compensatory strategy. Only very specific evolutionary trade-offs allow evolutionary stability of strategies that coexist through relative nonlinearity. As we find no reason why these particular trade-offs should be abundant in nature, we conclude that sympatric evolution of relative nonlinearity seems possible, but rather unlikely. We speculate that this may explain why relative nonlinearity has seldom been observed, although we note that a low probability of sympatric evolution does not exclude the possibility that this mechanism of coexistence might still frequently occur when species with different evolutionary histories meet in the same community. Our results highlight the need for combining ecological and evolutionary perspectives for understanding community assembly and biogeographical patterns.