Biodiversity-ecosystem functioning relationships in freshwaters: a food web perspective

Ecosystem processes and community structure are inextricably linked, as revealed by the (usually positive) 'biodiversity-ecosystem functioning' (B-EF) relationships that have been described increasingly in recent years. Because environmental stressors associated with human activity are causing significant declines in biodiversity across Europe, this threatens to disrupt the normal functioning of natural systems. At present, however, the potential impacts of biodiversity loss on ecosystem processes and, ultimately, on the supply of 'goods and services' of socioeconomic value (e.g. the supply of clean water; recreational fisheries) are poorly understood in freshwaters. This lack of knowledge is further compounded by the fact that most B-EF experiments have been restricted to single trophic level systems in terrestrial grasslands, and as such they lack generality. Multi-trophic systems (i.e. most real ecosystems) can behave very differently: this is particularly true in freshwaters, where predator-prey interactions can have profound effects on ecosystem processes. Further, the diversity of species 'traits' may be more important than taxonomic diversity per se, especially in systems where species are trophically similar, as appears to be true of many freshwater food webs. Indeed, B-EF curves in stream systems often reach saturation at low levels of species richness (typically about 3 species per guild). A further important shortcoming of many B-EF experiments is that they have assemblages that have been constructed by random sampling from a species pool, whereas species-loss is highly non-random: taxa that are big, rare and/or high in the food web are often the first to be lost. The proposed research has been designed to address these shortcomings of previous B-EF research, with a particular focus on applying a more realistic food web perspective. Specifically, we will investigate how non-random species loss affects multiple ecosystem processes (decomposition, primary production, herbivory) that determine the flux of energy to the higher trophic levels, which are often of high socioeconomic value (e.g. salmonid fishes). Focussed laboratory trials will be combined with field surveys and manipulations to explore mechanisms behind B-EF relationships in multitrophic systems, with an emphasis on trait (as opposed to simply taxonomic) diversity. We will approach these questions from two directions: 1) a Postdoctoral Research Assistant will explore, experimentally, the consequences of biodiversity change for ecosystem functioning and 2) a Tied PhD student will focus specifically on the potential impacts of climate change, which has been identified as a major stressor for freshwaters over the coming century, by using a combination of surveys, experiments and mathematical modelling.