Food web structure exceeds the effects of precipitation on ecosystem function Trzcinski, M. Kurtis; Srivastava, Diane S.; Corbara, Bruno; Dézerald, Olivier; Leroy, Céline; Carrias, Jean-François; Dejean, Alain; Céréghino, Régis
Ecosystems are being stressed by climate change, but few studies have tested the food web responses to changes in precipitation patterns and the consequences to ecosystem function. Fewer still have considered whether results from one geographic region can be applied to other regions, given the degree of community change over large biogeographic gradients. 2. We assembled, in one field site, three types of macroinvertebrate communities within waterfilled bromeliads. Two were inspired by the multi-channel food webs found in Costa Rica and Puerto Rico and one by the structurally simpler food webs in French Guiana. We manipulated the amount and distribution of rain entering bromeliads, and examined how food web structure mediated ecosystem responses to changes in the quantity and temporal distribution of precipitation. 3. Food web structure affected the survival of functional groups in general, and ecosystem functions such as decomposition and the production of fine particulate organic matter. Microorganisms and metazoans were more resistant to drought than ecosystem function. In our experiments, the sensitivity of the ecosystem to precipitation change was primarily revealed in the food web dominated by the single mosquito-microbial channel because other top-down and bottom-up processes were weak or absent. 4. Our results show stronger effects of food web structure than precipitation change per se on the functioning of bromeliad ecosystems. Consequently, we predict that ecosystem function in bromeliads throughout the Americas will be more sensitive to changes in the distribution of species, rather than to the direct effects caused by changes in precipitation.
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