Hydrology shapes taxonomic and functional structure of desert stream invertebrate communities

Hydrology is a fundamental factor influencing ecosystem dynamics, life-history strategies, and diversity patterns in running-water habitats. However, it remains unclear how hydrology may structure the taxonomic and functional composition of communities, especially in systems with high spatiotemporal variability in flow. We examined invertebrate diversity from 7 desert streams in the Huachuca Mountains of southeastern Arizona, USA, that span a flow permanence continuum from highly intermittent to perennial. We examined the relative roles of flow permanence, habitat size, season, and microhabitat in determining taxonomic and functional structure (according to 7 species traits compiled for 234 taxa) of these communities. We predicted that both functional and taxonomic diversity would be positively related to flow permanence and negatively related to the duration and number of stream drying events. As predicted, increased flow permanence was associated with increased functional richness, functional evenness, and taxonomic richness. Conversely, drying events reduced functional diversity across all measured indices. We found a saturating relationship between functional richness and taxonomic richness, indicating functional redundancy in species-rich communities, which may promote resilience of ecosystem function to environmental variation. Our study adds further evidence that hydrology is a key determinant of aquatic invertebrate diversity, and that stream hydroperiod strongly influences both functional and taxonomic diversity in arid-land streams.