A long-term study of the factors that influence compositional stability of stream invertebrates

Long-term studies have seldom considered the compositional stability (i.e., invariability of community composition) of stream invertebrate communities. Compositional stability could potentially be related to variations in species richness, habitat complexity, or hydrological and physicochemical conditions. Invertebrate species data were obtained for 21 sites that had been sampled over 16 to 20 years in Victoria, southern Australia. Stability of community composition at a site was measured with the mean Bray-Curtis coefficient, which was calculated for all comparisons between samples taken over the sampling period using only presence/absence data. Three datasets were compiled: one containing all species, one containing only insects, and one with family-level data. Multiple regressions demonstrated that stability at a site was related directly to species richness and habitat complexity and inversely to daily discharge; stability was not related to physicochemical conditions. The first 2 factors accounted for 45–49% of the variance while flow accounted for 9–16% but was not significant at the family level. The positive relation between stability and species richness may be due to higher variability in colonization at species-poor sites and thus lower compositional stability, while increased habitat complexity enhances stability by providing more refuges. Increased flow may result in more invertebrate drift and movement and thus lower stability, but the relationship was weak and provided little support to the idea that hydrology is an important ecological characteristic for invertebrates of southern Australian rivers.