Biodiversity and ecosystem functioning

The relationship between biodiversity and ecosystem functioning is an important research question (Chapin et al. 2000) with obvious practical implications. Although it is impossible to fully cover all aspects of ecosystem functioning in a project of the size of PONDSCAPE, we here develop a strategy to reveal key aspects of the links between taxon diversity in focal organism groups and specific ecosystem functions. We will apply our approach to a subset of the ponds in the survey outlined in WP1 as well as to the studies on the impacts of age (WP2) and management techniques (WP4). Our approach does, therefore, not involve specific designs to disentangle the impact of biodiversity from that of species composition (e.g. the large-scale experiments such as outlined in Tilman et al. 1997). Rather, we look for relationships at the phenomenological level, i.e. as they can be observed and quantified in the field.

Bacteria are, because of their fast metabolic and population growth rates and their capacity to transform a broad array of (mainly organic) compounds, at the heart of the cycles of material in ecosystems. We will therefore focus on qualitative and quantitative aspects of resource use and other functional attributes of the microbial communities to characterize the functioning of selected pond ecosystems. These measures of functionality take the whole microbial community into consideration, and therefore do not reveal which taxon engages in which transformation. This is intrinsic to the limitation that most microbial organisms cannot be cultured. However, as we also quantify bacterial diversity using molecular techniques as part of WP1, WP2 and WP4, we will be able to directly relate functional characteristics and functional diversity of the bacterial community with taxon diversity of the bacterial community. In addition, we will broaden this approach by also incorporating diversity estimates of the other organism groups in this analysis. This is highly relevant, as it is, for instance, known that community composition of phytoplankton and zooplankton can strongly influence bacterioplankton communities (Muylaert et al., submitted).  Relationships between ecosystem functioning and biodiversity levels have thus far mainly been assessed in terrestrial ecosystems; this is one of the first such studies in freshwaters.