Evolutionary Rescue

Populations that experience severe stress may avoid extinction through adaptation by natural selection. This process is called evolutionary rescue and has been studied under different names in medicine, agriculture, and conservation biology. It is a component of the emerging field of eco-evolutionary dynamics, which investigates how the ecological attributes of species may evolve rapidly under strong selection. Its distinguishing feature is to combine the evolutionary concept of relative fitness with the ecological concept of absolute fitness in a synthetic theory of persistent adaptation. The likelihood of rescue will depend both on attributes of the population, particularly abundance and variation, and on properties of the environment, particularly the rate and severity of deterioration. Medical interventions (e.g., the administration of antibiotics), agricultural practices (e.g., the application of pesticides), and population ecology (e.g., the effects of species introductions) provide numerous examples of evolutionary rescue. The general theory of rescue has been tested in laboratory experiments with microbes, in which experimental evolution shows how different treatments affect the frequency of rescue. Overall, these experiments have supported the predictions of general theory: In particular, abundance, variation, and dispersal have pronounced and repeatable effects on the rescue of populations and communities. Extending these laboratory results to the field is a major task for future research.