Project A20

The role of individual tolerance for community assembly during degradation and recovery

Hypothesis 1 Hypothesis 1 Hypothesis 1 ARC 2 ARC 3 Models Synthesis Bacteria Fungi Protists, autotroph Invertebrates Fish

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.

PhD topic(s)

Helena Soraya Bayat (University of Koblenz-Landau)

The role of individual tolerance in community assembly during degradation and recovery

Multiple stressor research aims to be able to predict the effects of multiple stressors as one of its primary goals and applications. Precise and accurate predictions of combined stressor effects can ultimately inform risk assessments and efforts to protect sensitive ecosystems most efficiently. Testing stressor combinations on relevant species can quickly spiral to incredibly time, work, and money intensive experimental designs, worsening with increasing ecological scale. This project makes use of readily available data, from single stressors on single taxa, to test if community effects of single and multiple stressors can be predicted. Community effects will also be compared across a range of contexts, notably during stressor impact and in the recovery phase as well as across geographical regions. The focus lies on three organism groups- algae, macroinvertebrates, and fish- and three stressors- salinity, temperature, and hydromorphological change.

The project tests three central hypotheses. First, that individual tolerances vary more between species in macroorganisms than microorganisms and that tolerance to salinity and temperature stressors increases with organismal body size. Second, that community change in response to a single stressor, and to a lesser extent multiple stressors, can be predicted from individual tolerance of component taxa; in the case of single stressors individual tolerances can predict the size of the response, and in the case of multiple stressors they can predict the direction of the response. Third, taxonomic and functional composition will be more predictable during stressor impact than recovery, with the lowest diversity during the phase of stressor action. The third hypothesis addresses the Asymmetric Response Concept (ARC). To test these hypotheses, a meta-analytic approach will be used to compile data from mesocosm studies on salinity, temperature, and hydromorphological stressors as well as tolerances for individual taxa from databases. Results of mesocosm experiments from around the world will be compared to the results of experiments from projects A03 and A08 within RESIST to put them in context. The results will clarify to what extent readily available tolerance data for single stressors can be used to predict multiple stressor effects on communities.


First Supervisor: Dr. Ralf Schäfer (University of Koblenz-Landau, Quantitative Landscape Ecology)
Second Supervisor: Prof. Dr. Sonja Jähnig (Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Ecosystem Research)
Mentor: Dr. Nadine Gerner (Emschergenossenschaft und Lippeverband)

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