ON THE CONSEQUENCES OF PREBREEDING AND POSTBREEDING COSTS IN THE EVOLUTION OF REPRODUCTIVE EFFORT TACTICS

Models of reproductive effort have generally concentrated on the evolu tion of total reproductive effort, without considering the option for specific components of effort to evolve. Further, most analyses have a ssumed postbreeding costs of reproduction. We present an optimization model that evaluates the option for components of effort with differen t temporal distributions of survival costs, affecting either adult sur vival before offspring independence (prebreeding cost) or survival aft er offspring independence (postbreeding costs). We assume that total a bsolute effort is fixed, and that the two components therefore, are co nstrained in their variation. The results show that, in most cases, op timal effort tactics that imply prebreeding costs must have lower marg inal effects on survival than tactics that imply postbreeding costs. O ur analysis also shows that the marginal benefits on effective fecundi ty of effort components may influence the optimal effort tactics. An a ge-structured version of the model shows that effort tactics implying postbreeding survival costs will be favored over effort tactics that i mply prebreeding costs, as the expectancy of future reproductive succe ss declines. We suggest that the temporal distribution of reproductive costs may have an important impact on the evolution of reproductive e ffort tactics, and emphasize the need for empirical studies evaluating the occurrence and consequences of prebreeding costs of reproduction.