Project leader

Prof. Dr. Ralf Bernhard Schäfer

Project Summary

A major aim of RESIST is to unravel the role of stressors, biotic interactions and dispersal in community assembly. This project focuses on the role of individual tolerance to stressors in community assembly during degradation and recovery. It takes a meta-analytical approach to confront the CRC hypotheses with results generated under a broad range of contexts. We will synthesise and analyse data from other projects of RESIST (e.g. A03, A08) and from single and multiple stressor experiments with communities from different biogeographical and environmental contexts. The project consists of two workpackages (WPs).

The first WP examines to which extent community composition under stressor impact conditions can be predicted from the individual tolerance of taxa. We will compile a database of single and multiple stressor experiments as well as individual tolerance data for the stressors selected for the CRC (salinization, temperature increase and hydromorphological change). We will explore predictive models to fill data gaps. The database will support other projects in their interpretation of results as well as in estimating values of parameters (e.g. A18, A19). The relationship between body size and individual tolerance as well as the variability in tolerance for different organism groups will be analysed to test the CRC's Main Hypothesis 2 (MH2). Tolerance distributions and rankings based on individual tolerance data will be compared to the responses of the taxa in the community context in single and multiple stressor studies. This comparison allows to evaluate CRC Main Hypothesis 1 (MH1) regarding the role of stressor tolerance for community assembly under stressor impact conditions.

The second WP examines the taxonomic and functional community change during phases of degradation and recovery. Functional analyses will largely be based on trait databases and consequently be restricted to organism groups for which such data are available. We will first calculate the taxonomic and, where feasible, the functional distance for the community data compiled in the first WP, updated with data from other CRC projects. We will test the hypothesis of a lower taxonomic and functional distance, and consequently variability between communities, during the phase of degradation in contrast to the recovery phase. Moreover, we will compute the taxonomic and functional diversity, in terms of taxonomic richness, functional richness and functional divergence, and analyse their trajectory over the different phases in the experiments. This allows to test the hypothesis that the taxonomic and functional diversity are lowest during the phase of stressor action and contributes to testing MH1 and MH3. Overall, by taking a meta-analytical approach the project delivers tests of the main hypotheses of the CRC related to the predictability of community assembly under stressor increase and decease, as well as a frame to synthesise the results of the CRC projects in conjunction with project Z03.