Phenotypic plasticity as a cause and consequence of population dynamics

Predicting how species respond to dynamically changing and novel environments is crucial for guiding conservation and mitigation strategies. Phenotypic plasticity is a mechanism of trait variation demonstrably important in determining how individuals and populations adapt to environmental change. The effects of phenotypic plasticity can be quantified in individuals by measuring environment-trait relationships, but it is often difficult to predict how phenotypic plasticity affects populations from environment-trait relationships alone. Variation in the life-history traits expressed by individuals may alter population processes, and this in turn can feedback to induce further variation in the traits expressed by individuals. This means the assumption that environment-trait relationships validated for individuals are representative of how populations respond to environmental change risks mischaracterising the effect of environmental change on populations. Predicting the effect of phenotypic plasticity on populations necessitates the development and utilisation of specialised predictive tools able to integrate empirically verified mechanisms of trait variation into a population's dynamical processes. We have derived a novel general mathematical framework linking trait variation due to phenotypic plasticity to population dynamics which we apply to the classical example of Nicholson's blowflies. This application reveals a rich set of counter-intuitive population-dynamical behaviours and highlights how seemingly sensible predictions about how environment-trait relationships generalise to population responses break down in the context of a populations dynamical processes. Our results demonstrate the importance of the interplay between phenotypic plasticity and population dynamics and the need to account for the effects of trait variation when making predictions about population responses to environmental change.