Unravelling processes between phenotypic plasticity and population dynamics in migratory birds

Abstract

Populations 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. Investigating the link between migration strategy plasticity and population dynamics can help to understand the regulation of migrant populations under environmental change. We first estimated population trends of migratory waterbirds in the face of the loss of staging habitat by using census data. We found increasing trends both in abundance and species richness in the remaining staging area, which we hypothesised was a consequence of behavioural plasticity generated by the loss of the historical suitable staging habitat. To test whether our hypothesis could explain observed trends, we constructed and analysed a full-annual-cycle individual-based model where each individual follows the same set of rules in the course of migration under a range of different staging habitat scenarios. Our empirical and theoretical results align well: 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.