Longevity hinders evolutionary rescue through slower growth but not necessarily slower adaptation

Abstract

Abstract“Evolutionary rescue” is the process by which a population experiencing severe environmental change avoids extinction through adaptation. Theory predicts when rescue is favored, but currently relies on assumptions of non-overlapping generations and therefore annual, semelparous life cycles. It has been hypothesized that longevity and iteroparity impede rescue by slowing rates of adaptation, although this hypothesis has rarely been tested. We develop a model with longevity determined by the balance of survival and reproduction and selection acting on survival through a quantitative trait. We analytically characterize the demography and evolution of cohorts, demonstrating that longevity allows repeated selection over the lifetime, with the surprising finding that this can decouple mean genotype and phenotype within a cohort. We then simulate populations at three longevities responding to environmental change. Under perfect trait heritability, longevity produces negligible differences in adaptation rates, but under low heritability, high-longevity populations experience a transient phase of rapid phenotypic change accompanied by slower genotypic change. More importantly, longevity is associated with slower intrinsic population growth rates regardless of trait heritability, ultimately hindering rescue. We connect these results to prior demographic and evolutionary theory and recent efforts to incorporate longevity into models of adaptation.