Ecology & Evolution of Species Range Limits

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All organisms are limited in geographic distribution, but how & why range limits occur are still poorly understood. This prevents realistic forecasting of whether species will shift ranges or go extinct during climate change and weakens effective conservation of Canadian species at risk most of which are at their northern limits in southern Canada. The goal of my research is to better understand the ecological and evolutionary processes that impose range limits over the short-term and prevent range expansion over the long term. My students and I will address this goal by filling 4 knowledge gaps described below, each of which is a missing piece of the range-limit puzzle. (1) A range limit is thought to occur where the environment reduces survival and reproduction sufficiently that populations are not self-replacing. Although species transplanted beyond their range often suffer, their reduced performance is often insufficient to limit the distribution. In such cases, dispersal may be limiting but how this occurs is unknown. A likely but untested hypothesis is that the range limit occurs where a species' dispersal into unoccupied habitat patches fails to keep pace with its extinction from occupied patches. (2) Across its range, a species may occur in a variety of habitats and the range of habitats occupied may narrow towards range limits. This may, in turn, reduce successful dispersal between habitat patches required for species persistence. However, whether habitat breadth changes at range edges has rarely been studied and underlying mechanisms are not understood. (3) Stable range limits are thought to occur where adaptation fails. Recent experiments have failed to reveal the necessary constraints on adaptation, but none have examined adaptation over multiple generations under natural conditions. (4) The capacity of peripheral populations to adapt to conditions beyond the range will be strongly influenced by reproductive mode. Plants often shift reproductive modes towards range limits, but whether this inhibits or facilitates geographic spread is unknown. We address these objectives using large-scale geographic surveys, manipulative transplant experiments and genomic analyses with plants species proven to be excellent experimental systems. This research will help answer fundamental questions at the forefront of biology and contribute to the conservation of species-at-risk, the management of exotic invaders, and better forecasting of species' responses to climate change; key environmental problems threatening Canadian biodiversity. My lab is an inclusive environment where diverse trainees at all levels learn highly transferable technical skills suited to their interests and long-term career goals in academia, resource management and industry. Ongoing partnerships with resource-management agencies broaden training and facilitate the transfer of information and skills between university researchers, government scientists and policy-makers.