How do Stream Confluences Influence Aquatic Invertebrate Taxonomic and Functional Diversity?

Aquatic communities, species that live and interact with each other, each have a unique composition and function (i.e collection of decomposers, predators, and grazers). Broad ecological theory provides a variety of models that can predict communities and their functions across riverscapes. For example, the River Continuum Concept (RCC) explains general shifts in stream communities and their function along longitudinal (upstream to downstream) gradients, but it fails to consider the more narrow effects of tributaries and confluences. Conversely, dendritic stream networks theory helps explain the potential role of river confluences and how they connect communities, but fails to explain general longitudinal shifts in communities. This discontinuity between models begs for a way to integrate the role of confluences (dendritic theory) into a broader landscape model (RCC). I hypothesized that river confluences would have a different influence on community diversity and function than expected under the RCC. To explore this, I sampled aquatic insects at tributaries along a watershed to test predictions that stream confluences would (1) increase insect diversity (number of species), (2) abruptly change specific species abundance, and (3) change the overall community function through increasing and decreasing insect functional feeding groups. I collected aquatic insects in two watersheds in the Beartooth-Absaroka Wilderness, sampling above and below four stream confluences in each watershed. Aquatic insect samples were identified to genus level and given a functional feeding group score. I will examine pairwise upstream/downstream differences with and without intervening confluences to compare community diversity, composition, and functional diversity. Streams ecosystems are often ranked as one of the most imperiled ecosystems in the world. Developing aquatic community theories and models as we work to restore these ecosystems is important in understanding how pristine aquatic ecosystems should function