Evolutionary rescue by adaptive specialization in rapidly changing environments

Theory suggests that a population with a narrower niche can adapt more rapidly to environmental change, all else being equal. However, a narrow niche may be correlated with other factors that compromise evolvability, such as a smaller population size, and it is unclear if specialist mutants can succeed by virtue of greater evolvability when impeded by the ecological costs of a narrower niche. Here we use simulation models to show that specialist mutants can invade during periods of rapid environmental change, in some cases preventing extinction. Focusing on asexual populations, we show that successful specialist mutants typically enjoy two types of advantages over generalists: an immediate benefit of ignoring a habitat in which they are particularly unfit, and a longer-term benefit of greater evolvability. By understanding the mechanisms that yield these benefits, we are also able to show that evolutionary rescue by specialization can be largely prevented by manipulating the schedule of environment change. Our results demonstrate how a population may change fundamentally under strong pressure to adapt rapidly, with implications for both beneficial (e.g., conservation) and harmful (e.g., antibiotic resistance) examples of evolutionary rescue.