Community synchrony declines under increasing environmental variability in aquatic macroinvertebrate communities.

Extreme weather events are increasing in frequency due to climate change, exposing ecological communities to higher environmental variability. Such variability can influence community abundance as species respond either similarly (synchronous dynamics) or independently (asynchronous dynamics). These fluctuations are important for understanding the impact of environmental variability on species temporal fluctuations in aquatic macroinvertebrates. This group of organisms is species-rich and highly sensitive to environmental fluctuations. We analyzed 18 stream macroinvertebrate communities sampled by the National Ecological Observatory Network between 2014 and 2022 to understand how community synchrony is related to stream temperature variability, discharge variability, and species turnover. We then quantified individual species contributions to community synchrony. These contributions were aggregated by functional feeding groups to understand how resource acquisition strategies influenced species contributions. Community synchrony was expected to be negatively related to increasing environmental variability and turnover. Consistent with this prediction, both temperature variability and turnover were negatively correlated with community synchrony, while discharge variability showed no relationship. Contributions to community synchrony varied across functional feeding groups. Filterers had the highest proportion of taxa with significant positive contributions, followed by gatherers, suggesting that taxa in these groups disproportionately contribute to synchronous dynamics. Scrapers had the lowest proportion of species contributing to synchrony. Using a standardized, long-term dataset, we demonstrated how temperature variability, turnover, and functional feeding groups relate to community synchrony. As climatic variability increases, whether species respond similarly or independently may have implications for long-term population and community persistence.