Diversidade e distribuição espacial de Ephemeroptera (Insecta) em riachos do Planalto Sul-rio-grandense, Brasil

Abstract

The additive partition diversity has been a promising method to analyze patterns of diversity in hierarchical studies. Streams are recognized for having a spatial structure hierarchically organized in increasing scales, ranging from places such as habitat, stretch, streams and the entire drainage system. The diversity and spatial distribution of mayfly nymphs communities were studied over four hierarchical spatial scales in Planalto Sul-rio-grandense (sampling units, substrates, streams and basin). Additionally, the influence of local environmental descriptors on the structure of the nymphs communities was tested. Samples were collected in 13 streams of two independent parts of the Planalto Sul-rio-grandense, in each stream were obtained 10 samples in falls five in stone substrate and five in leaves. The spatial distribution of mayfly nymphs showed structuring according to types of substrates sampled. The partitioning of diversity among the analyzed scales revealed that the major portion of beta diversity occurred between the sampling units and between the streams of the same dimension and a very small amount in the range of substrate. Thus, we assume that the fauna of aggregation in the smaller spatial scale was not due to substrate differences associated with rapid but the variation between rapids, reflecting the predominance of specific processes related to the availability of resources. We assume also that the nymphs of ephemeral not have barriers to the use at these substrate, which could actively move between the rapids of streams. In addition, the diversity that occurs between streams of the same part, can be attributed to local characteristics of each stream, such as slope, conductivity and current velocity. Finally, three environmental descriptors (altitude, slope, and dissolved oxygen) were important to structure the mayfly community at the streams of Planalto Sulriograndense. We conclude that the scales from rapids (sampling units) and between streams are scales that have the largest portion of the variability of the taxonomic composition showing to be more effective in assessing the spatial variation of mayfly nymphs communities.