Seasonal compensation of predation and harvesting

Compensatory mortality or natality can operate as a consequence of seasonally driven mechanisms of density dependence. Our objective is to clarify the relationship between compensation and density dependence in population models for vertebrates when seasonality is present. Field studies of a variety of species have demonstrated that due to compensation, predation or human harvest may not influence spring-breeding or pre-harvest-season densities. Compensation seems to contradict most harvesting and predation models because these models predict that harvests or predation will always reduce equilibrium population size. In these population models sustainable harvests are attainable because of density dependence. The apparent discrepancy is attributable to the failure of most population models to incorporate the details of environmental seasonality. We review seasonally explicit models of population dynamics to illustrate how density dependence is the mechanism behind compensatory mortality and natality. Even though spring-breeding or pre-season densities can remain unaffected or even increased by harvesting, harvesting or predation generally reduces the integral of population size. Compensatory mortality and natality are often cited as the basis for sustainable harvests of wildlife populations.