Environmental heterogeneity, dispersal mode and habitat specialisation modify within-site beta diversity of spring macroinvertebrates

Spring helocrenes are a unique aquatic environment with high biotic diversity. Although environmental heterogeneity has traditionally been assumed to explain the high species richness of spring habitats, this assumption has never been properly tested. Here, we sampled macroinvertebrates from two calcareous helocrenes in Slovakia with visually distinguishable mesohabitat heterogeneity. We hypothesise that macroinvertebrate beta diversity significantly increases with environmental heterogeneity even at a small within-site spatial scale. We also examined four species-trait categories, that is, active or passive dispersers and habitat specialists or generalists. Significant spatial structuring of environmental heterogeneity was found at one site, whereas the other site did not show a clear spatial pattern. Strong associations were found between beta diversity of all species trait categories and environmental heterogeneity at the first site, while there were virtually no associations at the second site. Specialists were not spatially structured at any of the sites examined. Our results suggest that invertebrate beta diversity responds positively to environmental heterogeneity at a site by also tracking spatial structuring of abiotic conditions. However, the response may vary depending on the dispersal mode and habitat specialisation of the invertebrates.