Effects of spatial distances on the assemblage dissimilarity of macroinvertebrates with different dispersal pathways and abilities in southern Brazilian streams

Abstract

The magnitude of distance–decay relationships (DDRs) in stream macroinvertebrates can vary with their preferential dispersal pathways (overland and watercourse) and abilities as well as with environmental dissimilarity. We assessed DDRs in the compositional dissimilarity of macroinvertebrate assemblages in southern Brazilian streams using overland and watercourse distances (WD) as explanatory variables. We conducted additional separate assessments for taxonomic groups and according to a classification that took into account differences in the dispersal abilities and main pathways among macroinvertebrates. Assessments were conducted separately for (a) strong‐flying insects with overland dispersal (Anisoptera), (b) weak‐flying insects dispersing preferably through riparian corridors (Chironomidae, Ephemeroptera, Plecoptera, Trichoptera and Zygoptera), and (c) watercourse dispersers (Mollusca, Psephenidae and Elmidae). The environmental dissimilarity associated with spatial extent was accounted for via partial Mantel tests. Overland and WD were positively correlated with the dissimilarity of the total macroinvertebrate assemblage, weak‐flying insects, watercourse dispersers, and most taxonomic groups. DDRs were stronger with overland than WD. However, no consistent pattern emerged after accounting for environmental dissimilarity. Strong‐ and weak‐flying insects were correlated with environment, while watercourse dispersers, with geographic distances. Additionally, taxonomic groups were differently related with environment and geographic distances. The distinct responses of each taxonomic group to the environmental specificities of the study area such as substrate composition and land use likely explain the observed results. Thus, our findings indicate that combining taxonomic and natural history information is an effective approach for comprehending the underlying mechanisms generating spatial structure in stream macroinvertebrate assemblages.