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Olivia Rahn, Anna Hargreaves
Predicting extinction and responses to environmental change across a species elevational range
Many formative hypotheses about the causes of species range limits presume that range limits occur at the points in space where species encounter the limits of their environmental niche, but in nature we find a variety of conflicting empirical evidence. While range limits are often concordant with niche limits, species range limits also sometimes fall short of niche limits, reflected in weak or non-existent declines in performance at species range edges. Additionally, recent synthesis work has shown us that the distribution of environmentally marginal habitat is only weakly correlated with geographic marginality. Furthermore, anthropogenic climate change continues to challenge our presumptions of where we should expect to find environmentally marginal habitat across a species range- previously harsh, cold areas may become increasingly optimal as global temperatures continue to rise, while previously optimal sites may become uninhabitable and experience population decline or extinction. This tells us that in order to accurately predict species performance across their geographic ranges in future climate change scenarios, we need to (a) disentangle our understanding of geographic and environmental marginality and (b) identify suitable predictors for population success in a changing world. In this study, we used long-term demographic data from an annual plant to test how well we can predict population extinction and persistence across a species elevational range in the face of environmental change. To do this, we ask 3 specific questions: (1) whether population success and stability over time vary across either the species geographic range or the species environmental niche, (2) whether geographic and environmental marginality are positively correlated with one another and (3) whether cool, marginal sites are performing better than warmer sites as annual temperatures in the region rise.
