Environmental Thresholds of Nepomorpha in Cerrado Streams, Brazilian Savannah.

Abstract

Determining thresholds of species loss in response to gradients of human impact is becoming an increasingly important component of stream conservation and management. We analyzed the thresholds of change in populations and communities of the infraorder Nepomorpha along a gradient of environmental integrity in streams of the Brazilian savannah, based on samples from 20 sites. We used the Threshold Indicator Taxa Analysis (TITAN) to identify the location and magnitude of changes associated with the environmental quality and the frequency and abundance of the different taxa. We also used TITAN to calculate the positive and negative thresholds of the community and species along the habitat integrity gradient. Nepomorphan species were generally associated with sites of higher environmental quality, which presented larger populations and greater species richness. Only a few nepomorphan species groups were associated with impacted streams. Thresholds were evident in some aquatic nepomorphan populations, but not for the community as a whole. This indicates that species have idiosyncratic responses to the environmental gradient, but in general nepomorphans appear to be a good indicator of healthy environments or less impacted streams in the Brazilian savannah.