Taxonomic distinctness and aquatic Coleoptera: comparing a perennial and intermittent stream with differing geomorphologies in Hidalgo, Mexico

Taxonomic distinctness combines species richness and phylogenetic diversity to detect changes in taxonomic structure. Most studies have reported on changes due to marine impacts, with little emphasis on habitat influences or freshwater systems. The composition and organizational structure of aquatic Coleoptera assemblages are susceptible to local influence, yet their colonization capacities suggest greater assemblage similarity over larger spatial scales. Surveys were conducted in two contrasting local streams (approximately 20 km apart), one intermittent with multiple stair-step cascades and intervening pools during the rainy season (and only pools during the dry season), and the other perennial with low gradient, in Hidalgo, Mexico. Published information from these initial surveys and their associated collections of adults were examined and the data converted to monthly presence/absence data for analysis using taxonomic distinctness. Despite reported physicochemical differences between the streams, only the average monthly proportion of swimmer species was significantly higher in the intermittent stream where elmids and psephenids were largely missing due to the general absence of protective substrate and the presence of pools; higher taxonomic structure was not affected. Well-developed colonization capabilities and a widely distributed species pool likely reduced detectable differences between the stream assemblages. Although the average monthly value of Sorenson’s Similarity Index for aquatic Coleoptera between both streams was low, differentiation was not achieved using taxonomic distinctness and presence/absence data.