Dissimilarity in the riparian arthropod communities along surface water permanence gradients in aridland streams

The riparian areas around streams and rivers are often thought of as distinct habitats with unique species. Research on riparian zones has traditionally focused on those bordering perennial waterways; thus, we know much less about riparian species supported by intermittent and ephemeral streams. As nonperennial streams make up the vast majority of stream channels in many landscapes, we aimed to investigate how surface water permanence affects riparian communities. We focus on riparian ground-dwelling arthropods, a group that often depends on resources derived from surface and/or ground water. We sampled riparian ground-dwelling arthropods along surface water permanence gradients in 3 replicated stream channels in southeastern Arizona to assess patterns in diversity and community similarity. We found that alpha diversity did not differ between reach types, but high species turnover led to significant community dissimilarity among perennial, intermittent, and ephemeral riparian zones. Further, intermittent and ephemeral riparian zones harbored more unique species not found at other reach types than did perennial reaches. These patterns were strongest during the dry season, when intermittent and ephemeral reaches are most likely to lack surface water. Our results suggest not only that the riparian zones of nonperennial streams host equivalent arthropod diversity to their perennial counterparts but also that these communities have little overlap with those at perennial reaches. As a result, intermittent and ephemeral stream channels should receive greater consideration than they currently do in efforts to conserve regional biodiversity.