Disturbance disrupts the relation between community similarity and environmental distance at small spatial scale

Abstract Aquatic invertebrate distribution within a fluvial network is affected both by dispersal capabilities of the species and changes in the environment along spatial gradients. Disturbance that affects part of the network may represent an abrupt change in environmental gradients, which should be reflected on its communities. We analysed whether the composition of benthic insect communities is associated to environmental and geographic distances in a small catchment, partially disturbed by a wildfire (non burned forest‐control: C, moderate impacted: I and burned zones: B). We postulated that changes in main resource availability differently affect certain functional feeding groups. We found that taxonomic differences were related to the disturbance condition but not to the distance among streams and that the effect of disturbance targeted mostly on shredders. Environmental differences were larger among C sites than among B sites, but community taxonomic composition was more similar among C than B sites. As a result, neither environmental nor geographic distances explained community similarity. When the analysis was scaled up by incorporating new data from a larger area, community similarity was explained both by environmental and geographic distance, independently (i.e. geographic and environmental distances did not correlate). Our results highlight the influence of a disturbance on the riparian vegetation on the benthic community composition and functional structure of forested streams, and showed the effect of scale in habitat association, as environmental and geographic distance together explained community similarity when the spatial scale was enlarged.