Biodiversity and aquatic food webs

Biodiversity in freshwater food webs can be considered in terms of the number of species occupying unique trophic positions or the number of species within a trophic position. Either can affect energy flow or biomass partitioning, and the two aspects of diversity may feed back on one another. This chapter analyses the importance of biodiversity in aquatic food webs on three different levels. First, it asks how varying diversity within trophic groups affects the outcome of trophic interactions. It then presents a conceptual framework and contrasts this model against experimental manipulations of consumer or prey diversity. Second, it asks how consumers and resources affect biodiversity within trophic levels. This question has a long history of experimental and modeling studies, and these are reviewed. The role of biodiversity at local and regional spatial scales for freshwater food webs is examined. Dispersal among local habitats can constrain local species diversity and influence the outcome of food web interactions. The interactive effects of the regional pool versus resident diversity on the outcome of trophic interactions are discussed.