The role of species' traits in dispersal across scales - from deep past understanding to present-day processes

A pressing challenge in ecology is to unravel the mechanisms that underlie the distribution of life at aglobal scale. Rare dispersal events across biogeographic barriers and establishment in new regions are central to this: these events determine the distribution of both the dispersing species and of species in the receiving community, and they can open opportunities for speciation. On smaller scales, dispersal is integral to species’ persistence, allowing them to respond to changes in their environment directly through movement or indirectly through adaptation. Not all species have the same ability to disperse and establish. Better understanding these differences has gained new urgency today if we are to accurately assess risks, challenges and conservation opportunities in the context of biological invasions, land-use and climate change. Species’ traits are thought to be an important factor in successful dispersal. For example, large species are often better dispersers than small species, and plants with seeds that can float are more likely to disperse over island archipelagos than those with seeds that sink. However, there have been few tests of theory on how species traits might support dispersal at large biogeographic scales. In this thesis, I combine biogeographic, macroecological and macroevolutionary approaches to identify the role of body size and life-history traits in dispersal, and to test the transferability of trait dispersal relationships across scales. First, I quantify and compare the role of traits in biogeographic histories of 56 tetrapod clades. Second, I discuss in a conceptual synthesis if and how information from macroevolutionary and biogeographic studies can be used to better understand species present-day biological invasions, as well as present-day extinction risk due to changing environmental conditions. Third, I test conceptual considerations from this work on empirical data, linking the patterns observed in past biogeographic dispersal to present-day biological invasions and range shifts. Together these three strands highlight the importance of taxonomic, geographical and temporal contexts in the role of species traits in dispersal, which is an important step forward to better predictions of species’ abilities to respond to changing environmental conditions