Often dry, never boring: the unique and specialized invertebrate communities of ephemeral streams

Authors: Michael T. Bogan, Kate S. Boersma, David A. Lytle

Year: 2010 (xlii)

Abstract

Ephemeral streams are frequently overlooked by ecologists, despite the fact that they are among the most common stream types in the world. Ephemeral streams serve essential roles, however, in many hydrological and biogeochemical processes in drainage networks, and may provide important dispersal corridors for both aquatic and terrestrial vertebrates and invertebrates. As part of a larger project examining the role of ephemeral streams in population connectivity between perennial stream reaches, we sampled aquatic invertebrate communities in 30 ephemeral streams in southern Arizona. While many taxonomic groups were mainly absent from ephemeral streams (e.g. caddisflies, mayflies), limiting higher-level taxonomic diversity, other groups were quite diverse. We documented at least 35 species of invertebrates from these streams, likely quite an underestimate given the limitations of larval identification for many groups. In general, ephemeral stream communities were comprised of a unique group of winter stoneflies (Capniidae), midges (Chironiomidae), beetle larvae (Dytiscidae), dobsonflies (Corydalidae), and blackflies (Simuliidae). Blackflies, in particular, seem widely adapted to ephemeral waters with many species known mainly from temporary streams. Even though many of our study streams had been dry for multiple years prior to sampling in January 2010, these communities exhibited relatively high taxa richness and abundance after only 5 weeks of continuous flow. Additionally, many of these specialist ephemeral stream species were rare or absent in adjacent perennial or intermittent reaches. This finding indicates that, in addition to their important roles in drainage-scale processes, ephemeral streams are also important contributors to regional species diversity.