The Demographic and Evolutionary Consequences of Selective Mortality: Predictions from an Eco-genetic Model of Smallmouth Bass

We use an individual-based eco-genetic model to examine the demographic and evolutionary consequences of selective mortality on a species with parental care, the smallmouth bass "Micropterus dolomieu" . Our analyses are grounded in a long-term (1936-2003) empirical study of the dynamics of two populations that differ widely in both density and life history. The model we construct extends previous approaches by including phenotypic plasticity in the age and size at maturation, by permitting density-dependent somatic growth, and by analyzing how costs associated with parental care alter model predictions. We show that, first, additional mortality on age-0 individuals applied for 100 years causes reduced population abundance and biomass, faster somatic growth rates, and phenotypic plasticity toward slightly larger sizes at maturation. Second, mortality on individuals above a minimum size limit, also applied for 100 years, has a small influence on population abundance and somatic growth, causes a reduction of biomass, as well as substantial evolution of the probabilistic maturation reaction norm leading to younger ages and smaller sizes at maturation. Third, the incorporation of body-size-dependent survival costs associated with parental care (i.e., by reducing the number of small breeding adults at high population densities, increasing the mortality of parents that breed at small body sizes, or increasing the mortality of offspring originating from small-sized parents), reduces the amount of evolution predicted to occur within 100 years. Together, these results underscore that selective harvest can cause both phenotypically plastic responses and rapid evolution, however, the rate and magnitude of the evolved changes are sensitive to a species life history characteristics.