The need for integrative approaches to understand and conserve migratory ungulates

Over the last two centuries overhunting, anthropogenic barriers and habitat loss have disrupted many ungulate migrations. We review the literature on ungulate migration disruptions and find that for many species the disruption of migratory routes causes a rapid population collapse. Previous research has focused on the proximal ecological factors that might favour migration, particularly spatiotemporal variation in resources and predation. However, this does not provide an adequate basis for understanding and mitigating anthropogenic effects on migratory populations. Migration is a complex behaviour and we advocate an integrative approach that incorporates population dynamics, evolution, genetics, behaviour and physiology, and that borrows insights and approaches from research on other taxa. We draw upon research on avian migration to illustrate research approaches that might also be fruitful in ungulates. In particular, we suggest that the migratory cycle should be evaluated in the context of seasonal population limitation, an approach we highlight with a preliminary demographic perturbation analysis of the Serengeti wildebeest (Connochaetes taurinus) population. We provide suggestions for avenues of future research and highlight areas where we believe rapid progress can be made by applying recent advances in theory, technology and analytical approaches.