Unravelling processes between phenotypic plasticity and population dynamics in migratory birds

Abstract

AbstractPopulations can rapidly respond to environmental change via adaptive phenotypic plasticity, which can also modify interactions between individuals and their environment, affecting population dynamics. Bird migration is a highly plastic resource-tracking strategy in seasonal environments. However, the link between the population dynamics of migratory birds and migration strategy plasticity is not well understood.The quality of staging habitats affects individuals’ migration timing and energy budgets in the course of migration, and can consequently affect individuals’ breeding and overwintering performance, and impact population dynamics. Given staging habitats being lost in many parts of the world, our goal is to investigate responses of individual migration strategies and population dynamics in the face of loss of staging habitat, and to identify the key processes connecting them.We started by constructed and analysed a general full-annual-cycle individual-based model with a stylized migratory population to generate hypotheses on how changes in the size of staging habitat might drive changes in individual stopover duration and population dynamics, and to identify the key processes connecting them. Next, through the interrogation of census data, we tested these hypotheses by analysing population trends and stopover duration of migratory waterbirds experiencing loss of staging habitat.We found empirical support for our modelling-identified hypotheses: the loss of staging habitat generates plasticity in migration strategies, with individuals remaining on the staging habitat for longer to obtain food due to a reduction in per capita food availability. The subsequent increasing population density on the staging habitat has knock on effects on population dynamics in the breeding and overwintering stage.Our results demonstrate how environmental change that impacts one energetically costly life history stage in migratory birds can have population dynamics impacts across the entire annual cycle via phenotypic plasticity.