Stage-structured cycles generate strong fitness-equalizing mechanisms

Abstract

For many organisms, rates of reproduction, growth and mortality depend on the amount of resources that an individual consumes. When resource abundances fluctuate through space and time, the realized life-history of an individual can change dramatically depending on the dynamics experienced. Previous studies have investigated the influence of resource-dependent rates on population dynamics, but none have considered how the feedback between non-equilibrium resource dynamics and resource-dependent life-histories influence natural selection and the maintenance of genetic diversity within populations. Here we demonstrate that different patterns of resource dynamics have a strong impact on natural selection in organisms with resource-dependent life-histories. Small-amplitude consumer-resource cycles, lead to lower rates of natural selection than do large-amplitude consumer-resource cycles. Parameterizing the model for a Daphnia-algal system, we demonstrate that resource-dependent life-history can explain the recently published observation that selection among Daphnia genotypes changed depending on the pattern of algal resource fluctuations. The characteristically asexual reproduction of Daphnia allows us to draw a much-needed link to the large body of competition theory that has emerged from community ecology. Our results reveal that the common ecological features of resource-dependent life-history and ontogenetic size-structure generate strong fitness equalizing mechanisms that likely contribute to the maintenance of diversity in natural systems.