Plastic reproductive allocation as a buffer against environmental stochasticity : linking life history and population dynamics to climate

Abstract

Empirical work suggest that long-lived organisms have adopted risk sensitive reproductive strategies where individuals trade the amount of resources spent on reproduction versus survival according to expected future environmental conditions. Earlier studies also suggest that climate affects population dynamics both directly by affecting population vital rates and indirectly through long-term changes in individual life histories. Using a seasonal and state-dependent individual-based model we investigated how environmental variability affects the selection of reproductive strategies and their effect on population dynamics. We found that: (1) dynamic, i.e. plastic, reproductive strategies were optimal in a variable climate. (2) Females in poor and unpredictable climatic regimes allocated fewer available resources in reproduction and more in own somatic growth. This resulted in populations with low population densities, and a high average female age and body mass. (3) Strong negative density dependence on offspring body mass and survival, along with co-variation between climatic severity and population density, resulted in no clear negative climatic effects on reproductive success and offspring body mass. (4) Time series analyses of population growth rates revealed that populations inhabiting benign environments showed the clearest response to climatic perturbations as high population density prohibited an effective buffering of adverse climatic effects as individuals were not able to gain sufficient body reserves during summer. Regularly occurring harsh winters ‘harvested’ populations, resulting in persistent low densities, and released them from negative density dependent effects, resulting in high rewards for a given resource allocation.