Abstract
BackgroundWe are interested in understanding if metacommunity dynamics contribute to the persistence of complex spatial food webs subject to colonization-extinction dynamics. We study persistence as a measure of stability of communities within discrete patches, and ask how do species diversity, connectance, and topology influence it in spatially structured food webs.Methodology/Principal FindingsWe answer this question first by identifying two general mechanisms linking topology of simple food web modules and persistence at the regional scale. We then assess the robustness of these mechanisms to more complex food webs with simulations based on randomly created and empirical webs found in the literature. We find that linkage proximity to primary producers and food web diversity generate a positive relationship between complexity and persistence in spatial food webs. The comparison between empirical and randomly created food webs reveal that the most important element for food web persistence under spatial colonization-extinction dynamics is the degree distribution: the number of prey species per consumer is more important than their identity.Conclusions/SignificanceWith a simple set of rules governing patch colonization and extinction, we have predicted that diversity and connectance promote persistence at the regional scale. The strength of our approach is that it reconciles the effect of complexity on stability at the local and the regional scale. Even if complex food webs are locally prone to extinction, we have shown their complexity could also promote their persistence through regional dynamics. The framework we presented here offers a novel and simple approach to understand the complexity of spatial food webs.
Highlights
The relationship between food web complexity and stability is amongst the most studied and debated questions in ecology
We have shown that complexity is a factor promoting the persistence of the food web at the regional scale once it is subjected to colonization-extinction dynamics
It is a considerable challenge to understand the ecological consequences of spatial dynamics in diverse and connected food webs
Summary
The relationship between food web complexity and stability is amongst the most studied and debated questions in ecology (see reviews [1,2,3,4]). The result would change quantitatively but not qualitatively if producers are more or less spatially aggregated, for instance because of facilitative or competitive interactions (see Discussion) With this simple extension of Holt [37], we predict that, for a perfect cascade, the persistence of a consumer species is a saturating function of the diversity of primary producers and is independent of its trophic rank. For webs that are intermediate between the perfect cascade and linear chain, we cannot find a general analytical solution for the fraction of available patches This solution is specific to the web topology and becomes rapidly complex with increasing species diversity because it requires tracking co-distributions between all pairs of prey species. We randomized the identity of prey or predator species in empirical webs to remove specific topological attributes, such as the degree distribution (number of trophic links per species) and distance to primary producers, while conserving others. These results imply that prey identity and the average distance to primary producers have no effect on persistence and that the degree distribution has a much stronger effect on persistence than the average distance to primary producers
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