Partitioning the Impacts of Spatial-Temporal Variation in Demography and Dispersal on Metapopulation Growth Rates

Abstract

Spatial-temporal variation in environmental conditions is ubiquitous in nature. This variation simultaneously impacts survival, reproduction, and movement of individuals and, thereby, the rate at which metapopulations grow. Using the tools of stochastic demography, the metapopulation growth rate is decomposed five components corresponding to temporal, spatial, and spatial-temporal variation in fitness, and spatial and spatial-temporal covariation in dispersal and fitness. While temporal variation in fitness always reduces the metapopulation growth rate, all other sources of variation can either increase or reduce the metapopulation growth rate. Increases occur either by marginalizing the impacts of temporal variation or by generating a positive fitness-density covariance where individuals tend to concentrate in higher-quality patches. For example, positive auto-correlated fluctuations in spatial-temporal variability in fitness generate this positive fitness-density covariance for under-dispersed populations, but decreases this covariance for over-dispersed populations e.g. migratory species. Negative autocorrelated fluctuations have the opposite effects. Positive covariances between movement and future fitness, on short or long timescales, increase growth rates. These positive covariances can arise is unexpected ways. For example, the win-stay-lose-shift dispersal strategy in negatively autocorrelated environments can generate positive spatial covariances that exceed negative spatial-temporal covariances. This decomposition of the metapopulation growth rate provides a way to quantify the relative importance of fundamental sources of variation on metapopulation persistence.