Time‐delayed effects on population dynamics can generate hidden costs of plasticity and enable coexistence

Inducible defences allow organisms to adapt to variable predation risk. Whether this is beneficial or not, however, depends on two traits: how accurately they can detect current predation risk and how rapidly they can switch between phenotypes. Here we use a two‐prey one‐predator ecological model to investigate how differences in accuracy and switching speed determine the outcome of competition between two plastic prey threatened by a shared predator. The prey species are identical in all other respects, thus assuming the absence of direct costs for being more accurate or faster. Despite this absence of costs, we often found ecologically stable coexistence between the prey, or competitive exclusion of the seemingly superior (faster or more accurate) prey. We show how these counterintuitive results emerge from a feedback loop between population dynamics and the traits regulating phenotype expression: very accurate or fast‐switching prey often altered predator–prey dynamics to their own detriment and to the benefit of their seemingly inferior competitors, and vice versa. Thus, differences in the regulation of phenotype expression allowed coexistence through a novel form of relative non‐linearity. The demonstrated trait–abundance feedback was critical for determining the long‐term fitness and survival of both prey, as this feedback causes the emergence of new costs of plasticity, which require consideration of the long‐term dynamics, and are thus not apparent when measuring costs in short‐term studies. Thus, we show that the adaptive value of plasticity may be limited by mechanisms not visible in many current empirical studies, which overwhelmingly focus on the immediate impact of plasticity on individual fitness. Read the free Plain Language Summary for this article on the Journal blog.