What drives detrital decomposition in neotropical tank bromeliads?
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Decomposition experiments that control leaf litter species across environments help to disentangle the roles of litter traits and consumer diversity, but once we account for leaf litter effects, they tell us little about the variance in decomposition explained by shifts in environmental conditions versus food-web structure. We evaluated how habitat, food-web structure, leaf litter species, and the interactions between these factors affect litter mass loss in a neotropical ecosystem. We used water-filled bromeliads to conduct a reciprocal transplant experiment of two litter species between an open and a forested habitat in French Guiana, and coarse- and fine-mesh enclosures embedded within bromeliads to exclude invertebrates or allow them to colonize leaf litter disks. Soft Melastomataceae leaves decomposed faster in their home habitat, whereas tough Eperua leaves decomposed equally in both habitats. Bacterial densities did not differ significantly between the two habitats. Significant shifts in the identity and biomass of invertebrate detritivores across habitats did not generate differences in leaf litter decomposition, which was essentially microbial. Despite the obvious effects of habitats on food-web structure, ecosystem processes are not necessarily affected. Our results pose the question of when does environmental determinism matter for ecosystem functions, and when does it not.
KeywordsContext dependency Ecosystem function Food webs Leaf litter Phytotelmata Rainforest
We thank Andrea Yockey Dejean for proofreading the English text, and Arthur Compin for preparing Fig. 1. We are grateful to the members of Hydréco (Laboratoire Environnement Petit Saut) for field and technical support. Two anonymous reviewers made valuable comments on an earlier version of the manuscript. Financial support was provided by the Agence Nationale de la Recherche throught the Rainwebs project (grant ANR-12-BSV7-0022-01) and an “Investissement d’Avenir” grant (CEBA: ANR-10-LABX-25-01). OD’s financial support was provided by a PhD fellowship from the Centre National de la Recherche Scientifique and the Fond Social Européen.
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