Assistant Professor Florida State University, Florida, United States
Abstract: Predation or harvest can alter traits in prey populations such as age at reproduction and growth. This can occur via selective pressure and evolutionary change, or indirectly via plastic effects (e.g., by reducing competition). These evolutionary and plastic changes interact to give rise to emergent life history traits in populations, but also are affected by extrinsic shifts or variation in environmental conditions (e.g., temperature or food availability). Yet these interactions between selective, plastic, and environmental effects remain understudied in terms of how they affect heritable and plastic variation in traits in harvested or heavily predated populations. We hypothesized that interactions between evolutionary and plastic effects of size-selective harvest might prevent or reduce harvest-induced life history evolution in an eco-evolutionary population model. This might be due to reduced overall selection on traits, or plastic trait changes dampening phenotypic expression of evolutionary change. To address how trait distributions of a population change when harvest occurs, and how this depends on the availability of a food source, we constructed an individual-based predator-prey model. Our model includes 1) genetic diversity, sexual reproduction and inheritance in the predator, 2) with a bioenergetic model of individual predator energy use, 3) dynamics of a prey population (food source), and 4) varying forms of harvest (representative of human harvest of fish) on the predator. Our model shows that food availability has strong evolutionary and plastic effects on life history traits, and these can prevent or buffer against the magnitude of life history trait changes due to harvest. This outcome persists across models meant to represent two different fish taxa (cod-like and herring-like). These results are in accordance with some recent findings from experimental and wild observational studies of the effects (or lack thereof) of harvest and food availability in fish populations. Our research suggests that understanding food availability for a harvested population is necessary for biological interpretation of change (or stasis) in that population's growth and life history trait distributions.
