Species interactions govern evolutionary and ecological effects of population harvesting

Abstract: Harvesting changes population abundance and can affect adaptation of several life-history traits. Harvesting can also have indirect effects ? effects on non-target species and secondary effects on target species ? because interactions between species in a community determine the relevant ecological and evolutionary feedback environment. Species interactions therefore influence the effect of harvesting on community structure and dynamics as well as on trait evolution. Yet, this problem has often been neglected. In this thesis I have studied how species interactions affect the response of target and non-target species to population harvesting, using multi-species models of population dynamics and trait evolution. I show that species? evolutionary and ecological responses to harvesting depend on the community context. Specifically, the direction and magnitude of harvest-induced evolutionary changes in a trait depend on (1) the type of species interactions, (2) the strength of species interactions, and (3) which individuals in the population that are affected by interspecific interactions. Harvest-induced changes in spatial abundance patterns depend on (1) traits that influence species interactions, (2) local species interactions in combination with migration, and (3) the interplay between migration and traits determining local population dynamics. This thesis shows that evolutionary responses to harvesting depend on multiple ecological processes, and, conversely, suggests that trait evolution influence how harvesting affects population abundance patterns. In conclusion, types of interspecific interactions that do not lead to a feedback between species can be disregarded when assessing qualitative harvesting effects on target species. In contrast, community feedback that results in indirect density-dependence or frequency-dependent selection needs to be accounted for in analyses of harvest-induced ecological and evolutionary effects on target and non-target species.