Research

Dispersal (i.e., movement between habitat patches) can have major consequences for individual fitness, species’ distributions, interactions with other species, population dynamics and stability. In light of the important need to predict how populations will respond to present-day threats from invasive species, habitat loss and fragmentation, and climate change, understanding causes and consequences of dispersal at the patch level is vital for population management and conservation. Empirical investigations have revealed several important factors regarding  emigration, the first stage of dispersal, particularly conspecific density. The paradigmatic view is that emigration increases with density; i.e. positive density-dependent emigration (+DDE). However, in an exhaustive review of the literature by our group, we found strong evidence for negative density-dependent emigration (-DDE) and density-independent emigration (DIE).

In fragmented habitats or at range boundaries, dispersal can be energetically costly to an individual, giving rise to  tradeoffs between reproduction and dispersal. However, such tradeoffs  and their consequences for population dynamics have scarcely been studied. Thus, important questions remain unresolved, such as: 1) is DDE beneficial or harmful to the population?, 2) Is a certain shape of the DDE function selected to hedge or buffer against detrimental effects such as habitat fragmentation or Allee effects?, and 3) what form of DDE would be selected to maximize fitness and survival given an explicit dispersal-reproduction tradeoff.

To help answer these questions, my research involves development of models based upon the reaction diffusion framework, mathematical and computational analysis of them, and biological interpretation. The reaction diffusion framework has been of enormous value in both empirical and theoretical investigations of spatial aspects.