Oastler Professor of Population and Community Ecology Yale School of the Environment New Haven, Connecticut, United States
Background/Question/Methods Over the last 30 years, our understanding of the factors that control the structure and function of coastal wetlands has shifted from a narrative that focused on bottom-up control to one that explicitly includes top-down factors. Recent studies have shown that the loss of predators in coastal salt marshes can lead to significant reduction of wetland extent due to overgrazing by herbivores. Such studies indicate that consumers may play a much larger role in the maintenance of wetland ecosystems than was previously thought. Therefore, the objective of this study was to evaluate whether altering top-down control by manipulating the presence of predators can lead to measurable changes in salt marsh ecosystem properties. Between May and August of 2015 and 2016, we established exclosure and enclosure cages within three coastal wetlands and manipulated the presence of macroinvertebrate predators to assess how consumers affect changes in ecosystem functions.
Results/Conclusions Predator presence was associated with changes in aboveground biomass and the rate of soil nitrogen absorption at one study site, while changes in other ecosystem processes were largely driven by bottom-up factors. These results challenge the recent consensus that consumers have strong effects, instead indicating that predator effects may instead be highly context-dependent.