COS 4-2 - The emergence of novel freshwater fish communities in the Anthropocene.

Abstract: Unprecedented changes in community composition that result in the emergence of novel ecological communities may be a feature of the Anthropocene, challenging the integrity and function of ecosystems and their management. Ecological communities in flowing freshwaters may be particularly vulnerable to these changes because of their exposure and vulnerability to a wide range of anthropogenic stressors. The goal of this study was to identify ecologically novel freshwater fish communities, and to quantify their rate of emergence across the globe. To achieve this goal we applied a new statistical method, previously only used for paleoecological data, to detect the emergence of ecological novelty across > 2400 communities of freshwater fish. We find novel ecological communities emerged in 17.5 % (95% CI: 16%-19%) of the fish communities surveyed over the last 50 years, with similar rates of emergence in Europe, North America and Australasia. However, while the emergence of novel ecological communities was relatively common, these changes tended to persist for multiple years in only 33% of cases, and were only associated with equally dramatic changes in functional composition in ~50% of cases. Our findings demonstrate that novel ecological communities in flowing freshwaters are a feature of the Anthropocene, but also provide evidence that dramatic changes in taxonomic composition may not always threaten the functional composition of freshwater fish communities.