Climate as driver of long-term trends in freshwater invertebrate communities

Long-term observations on riverine invertebrate communities are crucial to assess potential impacts of climate change on stream ecosystems. In my talk I will present results from three recent studies: In the first study we examined LTER data (10–32 years) of 26 streams and rivers from four European ecoregions, to investigate invertebrate community responses to changing climatic conditions. Taxa and ecoregions differed substantially in their responses. We did not observe overall changes in total taxonomic richness or abundance over time or with increasing temperatures, probably due to compensatory turnover in the composition of communities (e.g., increasing number of invasive species favored by extreme events). However, we found an apparent upstream community movement and changes in functional feeding group diversity, indicating that climate change may be associated with changes in trophㄣic interactions within aquatic food webs. In a second study we analyzed long-term data (1969-2010) of aquatic insects from a nature reserve. Here we showed that over the 42 years a 2°C warming and changes in discharge regime have caused a 82% decline in abundance and a 54% increase in turnover of freshwater insect communities. Moreover, the community phenology has changed towards a longer duration and an earlier peak of emergence. In a third study, we analyzed the changes in the temperature signature (i.e., weighted temperature preferences of species within a community) and community composition of invertebrate communities over 25 years, based on 3,782 samples over large elevational, latitudinal and longitudinal gradients in central Europe, where we registered a warming of 0.5 °C. The temperature signature of stream invertebrates increased at a similar pace as temperature did, indicating a thermophilization of the communities. The strongest changes occurred along the altitudinal gradient, indicating that stream invertebrates use the spatial configuration of river networks to track their temperature niche upstream. Moreover, community composition has profoundly changed: the community share of cold-dwelling species has declined by 31% and 41% in terms of total abundance and taxonomic richness, respectively. Locally, such a decline was compensated by an increase in medium-temperature and warm dwellers. All three studies provide evidence that climate change already induce changes in abundance, richness, turnover and trophic structure, which could be regarded as early indicators of an ongoing process towards a homogenization of freshwater communities. Besides, the need to further explore the interactive effects of climate change variables with other local stressors to develop appropriate conservation measures became evident.

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