Phenotypic plasticity as a cause and consequence of population dynamics

Predicting complex species‐environment interactions is crucial for guiding conservation and mitigation strategies in a dynamically changing world. Phenotypic plasticity is a mechanism of trait variation that determines how individuals and populations adapt to changing and novel environments. For individuals, the effects of phenotypic plasticity can be quantified by measuring environment–trait relationships, but it is often difficult to predict how phenotypic plasticity affects populations. The assumption that environment–trait relationships validated for individuals indicate how populations respond to environmental change is commonly made without sufficient justification. Here we derive a novel general mathematical framework linking trait variation due to phenotypic plasticity to population dynamics. Applying the framework to the classical example of Nicholson's blowflies, we show how seemingly sensible predictions made from environment–trait relationships do not generalise to population responses. As a consequence, trait‐based analyses that do not incorporate population feedbacks risk mischaracterising the effect of environmental change on populations. We develop a novel mathematical modelling framework for representing the effects of phenotypic plasticity on populations. Applying the framework to the classical example of Nicholson's blowflies, we show how unintuitive population dynamical phenomena can emerge as a consequence of simple mechanisms of phenotypic plasticity. We demonstrate that to properly account for the effects of trait variation one must take an integrated approach, considering the response of both individuals and populations to environmental change, and that failure to do so may lead to erroneous conclusions.