Together or separately: two distinct modes of predator-prey distributions in space

Background/Question/Methods The composition of ecological communities may vary significantly over space, even between neighboring local sites within the same region. Therefore, regional species diversity is mediated simultaneously by locally, within-site coexisting species (alpha-diversity) and by between-site variation among local communities at the regional scale (beta-diversity). However, although it is accepted that connectivity between sites is important for maintenance of species diversity, it is unclear what the relative roles of alpha- and beta-diversities are and how they are affected by changes in connectivity. In this talk we focus on predator-prey or consumer-resource populations, which are fundamental components of ecological communities. We will present our extended metapopulation model that explicitly accounts for both within-site and between-site dynamics. We will demonstrate comparison of our theoretical results with empirical data from a variety of microcosm experiments and from long-term, large-scale monitoring projects.

Results/Conclusions We will first present our theoretical results showing that moderate connectivities between sites, above a certain threshold, promote coexistence that relies heavily on beta-diversity, whereas high connectivities promote coexistence that relies more heavily on alpha-diversity. Furthermore, the mechanism underlies each of these two modes of coexistence is very different: Alpha-mediated coexistence is due to (partial) synchrony between sites, whereas beta-mediated coexistence is maintained by a local turnover between (i) empty sites; (ii) sites occupied primarily by predators; and (iii) sites occupied primarily by prey. Analyzing datasets from both microcosms and natural ecosystems demonstrates that communities rely on a combination of these two mechanisms, but the relative role that each mechanism plays varies significantly between ecosystems. Finally, we will show that a negative spatial-correlation between predator and prey may be a warning signal for community collapse.