The paradox of enrichment in metaecosystems.

Isabelle Gounand,Céline Hauzy,Elsa Canard,Nicolas Mouquet,Dominique Gravel,Frédéric Guichard

doi:10.1086/678406

Abstract

The paradox of enrichment has been studied almost exclusively within communities or metacommunities, without explicit nutrient dynamics. Yet local recycling of materials from enriched ecosystems may affect the stability of connected ecosystems. Here we study the effect of nutrient, detritus, producer, and consumer spatial flows-combined with changes in regional enrichment-on the stability of a metaecosystem model. We considered both spatially homogeneous and heterogeneous enrichment. We found that nutrient and detritus spatial flows are destabilizing, whereas producer or consumer spatial flows are either neutral or stabilizing. We noticed that detritus spatial flows have only a weak impact on stability. Our study reveals that heterogeneity no longer stabilizes well-connected systems when accounting for explicit representation of nutrient dynamics. We also found that intermediate consumer diffusion could lead to multiple equilibria in strongly enriched metaecosystems. Stability can emerge from a top-down control allowing the storage of materials into inorganic form, a mechanism never documented before. In conclusion, local enrichment can be stabilized if spatial flows are strong enough to efficiently redistribute the local excess of enrichment to unfertile ecosystems. However, high regional enrichment can be dampened only by intermediate consumer diffusion rates.

Highlights

Rosenzweig (1971) defined the paradox of enrichment as the destabilization of consumer-resource dynamics observed after resource enrichment
We found that nutrient and detritus spatial flows are destabilizing, whereas producer or consumer spatial flows are either neutral or stabilizing
We explored a range of diffusion rates from low to high compared with the rate of local dynamics

Summary

Introduction

Rosenzweig (1971) defined the paradox of enrichment as the destabilization of consumer-resource dynamics observed after resource enrichment. Several mechanisms have been invoked to explain why this destabilization might not happen in complex ecosystems (for a review, see Roy and Chattopadhyay 2007). These mechanisms include factors relative to the resource species that limit the nutrient input to the consumer, such as unpalatability, lower quality, inducible defenses, refuges, or alternative resources (Urabe and Sterner 1996; Genkai-Kato and Yamamura 1999; Van Baalen et al 2001; Verschoor et al 2004; Vos et al 2004). Stability emerges from factors that increase nutrient output from the consumer, such as cannibalism (Chakraborty and Chattopadhyay 2011), parasitism (Hilker and Schmitz 2008), interference (Auger et al 2006; Cabrera 2011), or trophic complexity (Trzcinski 2005)

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Conclusion