Evolving dispersal and age at death

Traditional, and often competing, theories on ageing agree that a programmed age at death must have arisen as a side effect of natural selection, and that it can have no adaptive value of its own. However, theoretical models suggest that ageing and programmed death can be adaptive. Travis J. M. J. suggested that if fecundity declines with age, a programmed age of death evolves through kin selection and that the nature of dispersal is crucial as it determines the degree of spatial structure and hence the strength of kin selection. Here, using a similar model, we consider the interplay between dispersal and age of death. We incorporate more realistic dispersal kernels and allow both dispersal and age of death to evolve. Our results show each trait can evolve in response to the other: earlier age of death evolves when individuals disperse less and greater dispersal distances evolve when individuals are programmed to die later. When we allow dispersal and age of death to evolve at the same time we typically find that dispersal evolves more rapidly, and that ageing then evolves in response to the new dispersal regime. The cost of dispersal is crucial in determining the evolution of both traits. We argue both that ageing is an overlooked ecological process, and that the field of gerontology could learn a lot from evolutionary ecology. We suggest that it is time to develop the field of ecological gerontology and we highlight a few areas where future work might be particularly rewarding.