In Phase I, A20 was the central RESIST project to compile individual tolerance data and to test hypotheses related to the role of tolerance in community assembly and differences between micro- and macroorganisms. We established the currently largest global database for thermal tolerance for macroinvertebrates and fish. We found no definitive link between body size and heat tolerance and the distribution of critical thermal maximum values were rather similar between fish and invertebrates. In a collaboration with A19, tolerance was the strongest predictor of stressor effects in the degradation phase, whereas biotic interactions became more important in the recovery phase, lending support to the Asymmetric Response Concept (ARC). In Phase II, A20 will use metacommunity modelling to understand and predict the role of ecological processes, namely dispersal, stochasticity and selection by local environmental and biotic factors, in response to multiple stressors and recovery. We will contribute to testing RESIST’s Main Hypothesis 1 and three projectspecific hypotheses related to the influence of dispersal, stressor profiles and stream network characteristics on community dynamics during degradation and recovery. First, we will establish spatially-explicit patch occupancy metacommunity models for the model catchments (Boye and Kinzig). The communities of diatoms, macroinvertebrates and fish will be synthesised to trait profile groups. Second, we will simulate metacommunity models on generic river networks that reflect a wide range of environmental contexts. This will be implemented at three spatial scales to examine scale-dependency of the ecological processes. We will examine how multiple stressors with different correlation structures and spatiotemporal profiles influence metacommunity dynamics and taxa richness. Finally, we will fit a model to a large Central European river catchment and examine the metacommunity response to water quantity and quality trends provided by A24. Overall, A20 adds a large-scale perspective to RESIST that addresses all ecological processes of the ARC and all stressors considered in RESIST.

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.

Contact: bayat@uni-landau.de

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)