Migration plasticity in ungulates: will it translate into increased resilience to global change?

Migration is an important component of ungulate behavioural tactics, that is tightly linked both to population distribution and to the function ungulates exert in ecosystems. The migration rate of several species has been observed to decrease, and climate change and anthropic pressure have been indicated as potential driving causes. The loss of migratory behaviour in ungulates could have paramount consequences on the ecosystems that encompass their seasonal ranges, on the one side, and affect population dynamics on the other. This talk has two main goals: first, I will re-establish the link between migratory behaviour definition, classification and emerging patterns, in ungulates; then, I will assess the causes – or determinants- of migration by looking at a multi-population movement dataset of a large herbivore in temperate climates, specifically the European roe deer. The analysis of movement trajectories through different methods allowed us to identify an inconsistency in the classification of migratory behaviour at individual level, that we attributed to individual plasticity. Such inconsistency might have profound consequences when assessing the prevalence of the migratory strategy at the population level, i.e. the fraction of migrants in a partially migratory ungulate population. We then moved forward, by acknowledging the emergence of movement patterns other than residence and stereotyped migration, and attempting to identify and describe them through two versions of an ‘index of migratoriness’, stemming from different analytical domains. Finally, we have integrated a spatial-explicit (or Cartesian)- based approach in identifying migratory patterns, with the underpinning determinants of migration. By using the concepts of ‘ecological distance’ and niche, we have developed a further ecological-based classifier of migration, and used this index to identify the migratory niche of European roe deer. Our multi-disciplinary, collaborative research contributes to understanding the complexity of patterns and ecological motivations that are normally referred to as migration, in ungulates. We offer a set of tools that can be applied on increasingly available movement datasets of ungulates. We suggest to re-shape the question ‘if ungulate are still migrating’ into ‘how ungulates are changing their movement patterns’, and to focus future research on the ecological profiles of such change. This applied approach should not only inform on the state of ungulate migration, but also on the components of the global change that are affecting it the most. This talk will thus stimulate the discussion whether this new knowledge on ungulate migratory behaviour should suggest management and conservation actions to favour and maintain migration, or if instead should be used to acknowledge the change in movement patterns as a form of reversible adaptive behaviour, impossible to control.