Adaption to gradual environmental change

While physiological and ecological responses to global environmental change have been the focus of numerous studies, research on evolutionary responses is lagging far behind. In particular, there is a lack of studies on potential feedbacks between ecological and evolutionary processes in changing environments. Species-specific differences in evolutionary rates could change community dynamics, while ecological processes such as species interactions and dispersal likely affect a species` adaptive potential. The fact that global change involves alterations in a multitude of environmental factors, with potentially interactive effects on both ecological and evolutionary responses, further complicates predictions of global change effects. The aim of the proposed project is to analyse ecological and evolutionary processes and their interplay in response (1) to multiple changing stressors, (2) to environmental change in trophically simple versus trophically complex communities, and (3) to environmental change in isolated versus connected habitats. Research questions will be analysed with a combination of modeling, microcosm and mesocosm experiments. A selection experiment lasting over hundreds of generations will expose several algal species to ambient and elevated levels of CO2 and temperature. Similarly, several ciliate species will be exposed to constant and elevated temperature. Reciprocal transplant experiments will test whether adaptation of algae to rising CO2 is influenced by a simultaneous increase in temperature. In addition, reciprocal transplant experiments will test whether species from different trophic levels (algae versus ciliates) differ in their adaptability to rising temperature. Reciprocal transplant experiments of the full community will test whether evolutionary processes affect community dynamics. Interactive effects of environmental change and habitat connectivity on ecological and evolutionary responses will be analysed in both a microcosm and a mesocosm experiment. The effect of rising temperature (microcosm experiment) and decreasing pH (mesocosm experiment), respectively, will be compared in isolated and connected habitats. Finally, a theoretical approach will combine the three research questions into one model. In a first step, evolution and environmental change will be integrated into a metacommunity model. Along a gradient of different dispersal and evironmental change rates, the importance of local adaptation versus tracking environmental change through dispersal will be compared. The model will then be extended by incorporating a second stressor and a second trophic level. Comparison of model and experimental results will serve to give insight into mechanisms potentially underlying the observed patterns.

Environments are changing at unprecedented rates. Climate change, eutrophication, pollution, and changes in land-use jeopardize biodiversity and the functioning of ecosystems. Organisms may be able to escape from extinction through environmental change by adaptation to the new conditions or by dispersal to more suitable habitats. In a series of experiments with microalgae, we tested if organisms can adapt to deteriorating environmental conditions and if dispersal between habitats can mitigate the negative effects of environmental change on biodiversity. In a laboratory experiment, six species of microalgae were exposed to increasing levels of salt. After six months of exposure, two species that were at the brink of extinction in these high salt environments at the beginning of the experiment were able to grow in these stressful conditions at the end of the experiment. However, while these adapted species were finally able to survive at high salt concentrations when grown in single-species culture, adaptation did not necessarily result in increased survival within a community of several species. In a second experiment, communities of microalgae were exposed to warming. Neither dispersal between habitats nor a slower rate of warming alleviated the negative effect of rising temperature on biodiversity. Interestingly, a number of species that preferred warm temperatures when grown in single-species culture went extinct at high temperatures when grown in communities of several species. Apparently, intensified competition between species was the reason for extinction at higher temperature rather than limited tolerance of high temperature. To test the effects of environmental change and dispersal in more complex communities, we conducted an experiment with natural aquatic communities in rain barrels. Environmental change and dispersal affected the community composition of algae, bacteria, and micro-crustaceans. Immigration alleviated the negative effect of environmental change on the biomass of algae, but did not mitigate the negative effect of environmental change on the biodiversity of micro-crustaceans. The results of these experiments show that interactions between species affect both evolutionary and short-term responses of species to environmental change. These results suggest that reliable predictions of the effect of global change on biodiversity need to take account of species interactions. In addition, we showed that dispersal between habitats can be of high importance in changing environments. Reduced dispersal due to changes in human land-use might thus intensify the negative effects of global change on biodiversity.