The research in my lab investigates the process of and limits to adaptation in plants with a focus on understanding the ecological and evolutionary processes that limit species distributions. Plants often exhibit variation in reproductive traits across geographic ranges providing opportunities to tackle unresolved questions concerning the evolution of sexuality vs. sexuality, outcrossing vs. self-fertilization, and dispersal. We also study biological invasions as an opportunity to study evolutionary adaptation in action, and apply the evolutionary and population genetic approaches to the management of plant species at risk.
We use a combination of large-scale geographical populations surveys, manipulative experiments in natural populations, genomic analysis of reproductive patterns & genetic structure, plus a variety of lab-based tools, including quantitative genetics, developmental analyses, image analysis, and computer modelling. Training includes a strong focus on quantitative and computational skills.
Our field work takes place in a variety of locations across North America and Europe. Currently, we have projects on the coevolution of geographic range limits and the mating system based on the pacific coast of North America, experimental and genomic analysis of elevational range limits in the Rocky Mountains of Canada, a large-scale analysis of adaptive evolution during biological invasion based in Europe and eastern North America, and studies of plant reproductive ecology at the Queen’s University Biological Station in eastern Ontario.
Evolution and ecology of range limits
Every species has a limited geographical range and there is tremendous variation, even among closely related species, in the size and position of the range. Over the short term, a species' range limit is set by a combination of abiotic factors and biotic factors that jointly affect population demography or metapopulation dynamics. From an evolutionary perspective, however, the fact that species ranges are limited over the long term poses a major problem: why doesn't natural selection cause populations at the range margin to adapt to their local conditions and spread outward? This directly questions the limits of adaptive evolution.
Recent theory proposes that ranges are limited because populations become increasing small, less productive and more sparsely distributed towards the margins of the range such that local adaptation at the range limit is thwarted by gene flow (m) from larger, more productive central populations. Plants pose a particular challenge for migration-selection models of range limits. Most have multifaceted reproductive strategies that combine sexual reproduction with clonal reproduction and inbreeding with outbreeding. And, reproductive mode can change drastically near the range limit and greatly affect population genetic diversity and gene flow in marginal populations. These reproductive shifts might shape the evolution of range limits by themselves or by interacting with other evolutionary forces.
We are testing ecological and evolutionary processes that limit species ranges by combining range-wide geographic surveys of population demography with reciprocal transplant experiments and population genetic analyses of genetic variation and gene flow. We have been studying species endemic to the coastal dune habitat of California (USA) and adjacent Oregon and Baja California (Mexico) because these species exhibit near-linear, 1-dimensional geographic ranges across habitat that is readily accessed and well-known botanically. To date our results challenge many of the assumptions and predictions of theoretical models that have been developed to explain range limits.
In addition to studies involving costal dune plants, as an experimental system, we are applying ecological and evolutionary models of range limits to investigate the factors impinging on peripheral populations of species that, in Canada, have been deemed “at risk”. Whereas almost all species-level conservation research in Canada is parochial in scope, focussing only on the populations at risk, our recent work shows that effective conservation of these northern peripheral populations requires that their demography and genetics be considered in the larger context of the species’ whole geographic range.