Using range-edge ecology to inform conservation of Canada's rare plants

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Most species considered imperilled in Canada only occur here at the northern edge of their geographic range. Species conservation in Canada is therefore inextricably tied to the ecology of range-edge populations. Yet little of the extensive ecological theory about edge populations or field techniques for studying them have been applied to Canada's species-at-risk to guide their conservation. For example, theory predicts that species' northern ranges are often limited by cold. If so, recent climate warming should be creating new habitat for many range-edge species, yet species-at-risk policy is focused on preventing loss of existing populations rather than helping species keep pace with climate change. We propose to combine our expertise on biogeography (AH), field experiments with range-edge populations (AH, MV), and Canadian plants at risk (JM) to help shift conservation of rare plants from simply preventing loss to promoting recovery. Questions: Using at-risk plants whose Canadian range is limited to southern Ontario and/or Quebec, we will ask two fundamental questions about edge populations that bear directly on their long-term conservation. 1) Is their northern range edge determined by ecological factors or dispersal? Dispersal limitation would mean their range could be bolstered by founding new populations; limitation by ecological factors (e.g. snow depth) would suggest mitigation strategies to bolster the size of existing populations (e.g. snow traps). 2) Is climate warming creating newly-suitable habitat north of species' current ranges? None of our candidate species' ranges have expanded despite five decades of warming; if new habitat exists they will need help getting there. Approach: First, we will use species distribution models to generate predictions about the ranges of 90+ rare species' in ON/QU. JM has successfully used distribution models to identify suitable habitat within species' ranges; we will increase models' geographic extent to identify potential habitat beyond them. We predict that species whose distributions are best predicted by temperature will be most likely to have suitable habitat beyond their range due to warming. Second, we will test model predictions using transplant experiments for 3 provincially-rare herbs. We will transplant seeds and cuttings to beyond-range sites that our models predict to be highly-suitable (treatment1) and moderately-suitable (treatment2) under current climates, monitoring to compare performance to control transplants within the range (treatment3). If plants perform well beyond their range, it suggests their distribution is dispersal limited; if transplants perform poorly, monitoring will reveal which ecological factors limit fitness. Better performance in treatment1 than treatment2 will validate models' ability to predict habitat; exceptions will reveal which models need refining. Third, we will re-run distribution models using future climate projections to predict where species' suitable climate will move. We will transplant plants to these 'future sites', surrounding half with experimental warming chambers to test whether plants could survive there given warming, or whether non-temperature factors will prevent warming-driven expansions.Impact: Canada's future biodiversity will be strongly shaped by dynamics of species range-edges. This project would help establish a scientific foundation for predicting such changes and identify effective recovery strategies for Canada's rare plants.