Local climates are shifting spatially in response to climate change and these shifts are increasing extinction risk for many species. Species that require a particular climate envelope, a suite of climatic conditions that contribute to their niche, are left with three possible outcomes when their climate envelope shifts away from their location: they can spread spatially to keep pace with the shifting envelope, they can adapt to the new climatic conditions, or they can go extinct. Assisted migration is an intervention that attempts to rescue populations facing extinction in response to shifting climate. This intervention involves transplanting individuals from the trailing edge to the leading edge of a population to help them keep up with their shifting climate envelope. We developed a stochastic population model to describe this process and inform hypotheses for testing assisted migration in a Tribolium microcosm experiment. We then established 60 replicate experimental microcosms and started them on a trajectory towards extinction by using a limited habitat envelope shifting at a fast pace. In half of the replicates we performed assisted migration by transplanting 100 individuals from the trailing edge of the population to the leading edge each generation.
Results/Conclusions
Simulation results suggest that assisted migration is sensitive to both the location where transplants are placed relative to favorable habitat and how frequently those assisted migration treatments are applied. Under the majority of simulated scenarios, assisted migration did not reduce extinction probability. Indeed, in some cases assisted migration increased extinction risk by disrupting the spatial structure of the population. In the Tribolium microcosm experiment assisted migration outperformed model predictions, showing substantially decreased extinction risk compared to controls. Control populations all went extinct as they fell behind the shifting habitat envelope, whereas most assisted populations kept pace with the envelope and maintained healthy population sizes. While our experimental results suggest assisted migration could be an effective conservation strategy, the lack of congruence with model predictions introduces a number of new questions, highlighting the need for more research into the fundamental mechanisms that contribute to the success of assisted migration. Without understanding these fundamental dynamics, conservation in the face of shifting climate envelopes will remain a challenge.