Higher genetic variance of prey defence promotes fluctuation-dependent species coexistence

Understanding stable coexistence of competing species despite the competitive exclusion principle has been a central topic in ecology. Previous studies revealed that rapid contemporary evolution can promote species coexistence, but the mechanisms behind coexistence are not fully understood. A recent study showed that predator evolution can promote fluctuation-dependent species coexistence. Here, I propose a new mechanism where prey rapid evolution due to high genetic variance can also promote fluctuation-dependent coexistence of competing predator species. Previous experimental and theoretical studies demonstrated that rapid evolution of a prey defence trait can cause predator-prey population cycles. Although those studies focused on a system with a single predator species, I show that the population fluctuations driven by prey rapid evolution can promote coexistence of two competing predator species via a gleaner-opportunist trade-off. By expanding the framework of modern coexistence theory, I further show how prey rapid evolution can increase the niche difference of competing predators and simultaneously affect the competitive ability difference via population cycles. Given the propensity for oscillatory dynamics and prey rapid evolution (due to large population sizes and genetic variance) in nature, I argue that this expansion of coexistence theory provides an important solution to the coexistence paradox.