Diversity and distribution of oligochaetes in tropical forested streams, southeastern Brazil

The distribution and beta diversity of oligochaete assemblages were investigated in different spatial scales to verify the influence of environmental factors and geographic distance on their structure. Two types of mesohabitats (riffles and pools) were sampled in eight first-order streams located in four preservation areas (Poço D’Anta Municipal Biological Reserve, Santa Cândida Municipal Biological Reserve, Ibitipoca State Park and a private farm called Fazenda Floresta) and two Atlantic Forest phytophysiognomies (Seasonal Semideciduous Forest and Rocky Field). Variations in the taxon richness, abundance and composition of the oligochaete assemblages occurred between streams and phytophysiognomies, but not between riffles and pools in the same stream. Low beta diversity values were found and both turnover and nestedness contributed similarly in the environments studied, which could have occurred because of the high capability of oligochaetes to adapt to different environmental conditions. Although the canonical correspondence analysis explained 85.5% of the data (first three axes), the partial Mantel test showed greater influence of geographic distance on the faunal composition than the environmental variables measured. Simple linear regression confirmed this result and showed that the decay of similarity increased with distance between streams. The information from this study sheds light on how environmental and spatial factors determine the variation in the distribution and diversity of oligochaetes in forested low-order streams.