Indirect human impacts turn off reciprocal feedbacks and decrease ecosystem resilience
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Creek bank salt marsh die-off is a conservation problem in New England, driven by predator depletion, which releases herbivores from consumer control. Many marshes, however, have begun to recover from die-off. We examined the hypothesis that the loss of the foundation species Spartina alterniflora has decreased facilitator populations, weakening reciprocal positive plant/animal feedbacks, resilience, and slowing recovery. Field surveys and experiments revealed that loss of Spartina leads to decreased biodiversity, and increased mortality and decreased growth of the ribbed mussel Geukensia demissa, a key facilitator of Spartina. Experimental addition of Geukensia facilitators to creek banks accelerated Spartina recovery, showing that their loss limits recovery and the reciprocal feedbacks that drive community resilience. Reciprocal positive feedbacks involving foundation species, often lost to human impacts, may be a common, but generally overlooked mechanism of ecosystem resilience, making their reestablishment a valuable restoration tool.
KeywordsAlternate states Facilitation Ecosystem recovery Foundation species Feedback loops
We thank M. Bevil and E. Suglia for assistance in the field and D. Sax, C. Peterson and anonymous reviewers for comments on the manuscript. This research was made possible by grant NSF BIO OCE-0927090 and the Brown University Undergraduate Teaching and Research Award Program.
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