Relaxed selection and environmental change decrease reintroduction success in simulated populations

Previous work has shown that captive environments can relax selective pressures on various traits, resulting in significantly more trait variance in captive-bred versus wild populations. This increased variance could be one cause of the high mortality rates observed when captive-bred populations are released into the wild, because a significant proportion of the released population exhibits traits that are no longer adapted to the wild. Here we use evolutionary simulation to examine the effects of relaxed selection on trait variance and population persistence when populations are reintroduced into static and changing environments. Our simulations show that when wild environments remained stable and selective pressures on given traits were quite strong (1) relaxation of selective pressures led to significant increases in trait variance; (2) trait variance rapidly decreased when pressures were restored; (3) the smaller the population size, the lower the probability of persistence; and (4) there was often a significant lag time between reintroduction and eventual extinction, reinforcing the importance of long-term monitoring after release. When captive-bred populations were reintroduced into changing environments, strength of selection in the release habitat was the factor that most influenced survivorship. Amount of change between the source and release habitat and the population's carrying capacity also influenced survivorship, but to a lesser extent.