Changes in seasonality resulting from global change are expected to have severe eco-evolutionary consequences on partially migratory populations. Despite, identifying life-history stages and locations controlling partially migratory populations persistence and growth rates is crucial to understand and forecast their population dynamics, it remains an open challenge. Thanks to new tracking technologies, long-term monitoring projects and associated statistical methods, the required data to address such questions is increasingly available for diverse species. However, general theoretical framework incorporating variation in partial migration and identifying fundamental principles of such systems is lacking. Here, we aim to fill this critical knowledge gap by developing full-annual-cycle models that capture key dimensions of demographic structure in seasonally varying environments. We achieve this by conceptualizing partial migration within a Leslie matrix model as the result of two variable vital rates: seasonal movement and its associated survival probability. This novel formulation allows us to investigate how metapopulation growth rate and its associated elasticities vary with partial migration. Further, we explore how the answer to these questions changes when we consider different levels of plasticity (e.g. fixed vs plastic movement) and life-history strategies (i.e. short vs long-lived species). Finally, we illustrate how our model can be parametrized with real data to investigate the dynamics of a partially migratory species, the European shag (Phalacrocorax aristotelis).
Results/Conclusions
We provide a new framework that allows to model partially migratory populations in varying environments. We show how partial migration can substantially affect population persistence and growth rate depending on the species life-history strategy, and its plasticity. The effects of partial migration were comparable with those traditionally though to drive population dynamics (i.e. survival or fecundity). These effects follow non-linear dynamics and can be magnified under certain conditions. Finally, we illustrate how this modelling framework can be parametrized for real species and used to answer relevant eco-evolutionary questions. For instance, we identify how potential increases in migration of the European shags could potential cause decreases in overall metapopulation growth rate. Overall, we extend demographic and evolutionary theory by addressing key knowledge gaps in partial migration modelling and show how to integrate new data sources on a real species to understand how seasonally mobile populations might respond under global change.