Data from: Do priority effects outweigh environmental filtering in a guild of dominant freshwater macroinvertebrates?

Abiotic conditions have long been considered essential in structuring freshwater macroinvertebrate communities. Ecological drift, dispersal, and biotic interactions also structure communities, and although these mechanisms are more difficult to detect, they may be of equal importance in natural communities. Here, we hypothesized that in ten naturally-replicated headwater streams in Eastern Switzerland, locally-dominant amphipod species would be associated with differences in environmental conditions. We conducted repeated surveys of amphipods and used a hierarchical joint species distribution model to assess the influence of different drivers on species co-occurrences. The species had unique environmental requirements, but a distinct spatial structure in their distributions was unrelated to habitat. Species co-occurred much less frequently than predicted by the model, which was surprising because laboratory and field evidence suggests they are capable of coexisting in equal densities. We suggest that niche preemption may limit their distribution and that a blocking effect related to the specific linear configuration of streams determines which species colonizes and dominates a given stream catchment, thus suggesting a new solution a long-standing conundrum in freshwater ecology.Little_Altermatt_priority_effects_dataData used in joint species distribution models of three amphipod species in headwater streams around Lake Constance, Switzerland. Data is based on surveys done four times, once each season, beginning in Spring 2015 and concluding in Winter 2016. Additional geographic information is included (elevation, land use) about sampling points and catchments; water chemistry measurements from each sampling visit; and a stream substrate habitat assessment from each sampling visit