Evolution of Life Histories in Response to Age-Specific Mortality Factors

Abstract

A life-history model from the literature (Schaffer 1974; Charlesworth and Leon 1976) is extended to study the relationship of life-history evolution to age-specific mortality factors. It is shown that an increase in mortality during one age class (j) selects for an increase in reproductive effort before and a decrease after the afflicted age class. However, density dependence in age classes subsequent to j could lead to an increase in reproductive effort for these ages. It is also shown that evolution of reproductive effort leads to the greatest proportionate withdrawal of reproductive value from those adult age classes plagued by new mortality factors. Hence, the commonly observed inverse relationship between reproductive value and mortality is provided with a theoretical underpinning. The smaller the existing survival through age j, the greater the evolutionary sensitivity of reproductive value and reproductive effort to changes in survival through age j. An application of the theory concerns Slobodkin's (1974) hypothesis of prey evolution, prudent predation, which is discussed. Extension of the results to mortality factors which affect multiple age classes is sketched.