Food Webs, Biodiversity, and Ecosystem Functioning

Various aspects of ecosystem functioning in food webs of different complexity is the focus of this chapter. The key common features of these contributions are the recognition that changes in diversity across ecosystems will almost certainly be distributed across multiple trophic levels, and that the interactions among species on those different trophic levels greatly complicate the prediction of possible consequences for ecosystem functioning. This focus contrasts with the prevailing tendency for recent models and empirical studies to consider diversity and functioning patterns within single trophic levels, usually primary producers. Other studies experimentally explore the consequences of variation in diversity in aquatic systems while focusing on either invasibility or total system productivity, while exploring the possibility of using position in the food web as a predictor of ecosystem responses to species loss or gain. It is unclear why studies of food webs and biodiversity and ecosystem functioning have proceeded along largely separate lines, but there are probably some practical reasons for the oversight. Experiments in a number of systems show that predators can either increase or decrease diversity across the entire community. Consequences of increased diversity within higher trophic levels are more difficult to predict, partly because of the complex ways that consumers can interact. Remarkably few empirical studies have compared the separate and aggregate impacts of different consumers on prey diversity, and even fewer studies have explored the consequences of multiple consumers on functioning.