Temporal community change in stream ecosystems varies by assemblage across US climates

Ecosystem properties are temporally dynamic. Temporal variability has been shown to decrease with increasing levels of biological organization (i.e. from population to community and ecosystem levels). However, patterns of temporal variability in community properties across assemblages are poorly understood. To address this gap, we used biotic sampling data for three distinct groups—algae, macroinvertebrate and fish—from the National Ecological Observatory Network wadeable stream sites, which span a broad hydroclimatic gradient across the conterminous United States, Alaska and Puerto Rico. We examined whether total temporal beta-diversity differed among assemblages and quantified the relative contributions of two mechanisms generating community dissimilarity: balanced variation (i.e. species replacing each other) and abundance gradient (i.e. species fluctuating in abundance synchronously). We also investigated whether the temporal scale of variation (seasonal vs. interannual) differed among assemblages and assessed patterns across a broad hydroclimatic gradient. We found that total beta-diversity was lower for fish assemblages, with average algae and macroinvertebrate temporal beta-diversity values 30% greater than average fish values. Algae and macroinvertebrates were more characterized by the balanced variation component, while fish were more characterized by abundance gradients. The temporal scale of variation did not vary among assemblages, with all three assemblages tending to vary mostly at the interannual time scale. Finally, we found that fish were more responsive to precipitation and discharge variability than algae and macroinvertebrates, but temperature variability and climate class did not drive beta-diversity patterns. Our work highlights that beta-diversity patterns and the processes behind them differ across assemblages, with systematic variation in body size and generation times likely explaining observed differences between algae, macroinvertebrates and fishes. Understanding how and why different groups show different levels of temporal stability is critical to anticipating ecological responses of aquatic communities to increasingly altered environmental regimes. Read the free Plain Language Summary for this article on the Journal blog.