One of the central goals of ecology is to understand how local and regional processes interact to give rise to patterns of biodiversity at multiple scales. This is particularly true in marine ecosystems, where the movement of propagules and nutrients is mediated by strong oceanographic currents that can couple the dynamics of communities across large distances. Although the effects of nutrient transport and propagule dispersal are well known when they are coupled in space, these two regional processes can become decoupled and spatially heterogeneous due to the passive nature of nutrients versus the active behavior of propagules. Here, we used a spatially-explicit metacommunity model to determine how differential coupling of nutrient transport and propagule recruitment in space affects tri-trophic (keystone) food webs. Specifically, we varied both the magnitude and the cross-correlation of nutrient and propagule movement to determine their relative influence on the (spatial) synchrony and stability (1/CV) of food webs at local and regional scales.
Results/Conclusions
When propagule dispersal and nutrient transport are spatially homogeneous and cross-correlated, increased movement always synchronizes and destabilizes the dynamics of food webs across scales. However, when nutrient transport and propagule dispersal are spatially heterogeneous, synchrony and stability become decoupled regardless of the degree of cross-correlation between nutrient and propagule movement. Indeed, full synchrony of all components of the food web can be associated with either low or high instability depending on the movement rate. Additionally, we found that increasing the cross-correlation between nutrient transport and propagule dispersal destabilized all compartments of the food web. This is due to trophic coupling of nutrients and organisms. When the cross-correlation is negative, sites receiving many organisms receive few nutrients and vice versa. Such trophic decoupling buffers local population growth and thus promotes stability at local and regional scales. The opposite is true when the cross-correlation is positive, which results in unbuffered local population growth and thus instability. Overall, our results reveal the importance of spatial heterogeneity and the differential movement of passive nutrients versus active propagules on the synchrony and stability of food webs across scales.