CONICET | Buscador de Institutos y Recursos Humanos

One of the most challenging aspects of quality indices has been to compile reliable measures of the species? sensitivity and tolerance to various magnitudes and different kinds of ecosystem attributes. Occupancy modelling has become increasingly useful to ecologists because provides a flexible framework to estimate the habitat use as a function of site information. We used oligochaete species and physicochemical variables of pampean streams to explore if the ecosystem attributes explained the occupancy of the species and how occupancy models would be useful describing the sensitivity of species along the range of attributes. We proposed three phases (resistance, tolerance and extinction) to describe the sensitivity of the species in terms of occupancy. Seventeen of the 33 taxa of oligochaetes detected were enough abundant to be modeled. In eight species, we obtained a total of 11 different models including water quality covariates. Occupancy was explained by conductivity in four species, by dissolved oxygen in three species, and by nutrients in four species. Occupancy modelling result in a valid and practical tool to describe the sensitivity of the most characteristic benthic species to ecosystem attributes. We were able to identify the three proposed phases in the theoretical model. Our modelling approach provides researchers with a tool for obtain reliable measures of the species? sensitivity. Further studies on the sensitivity of local species after subjection to different types of pollutants will, however, be required in order to complete the spectrum of bioindication for the oligochaetes. With the new methodology provided here, ecologists dedicated to the study of sensitivity and the generation of biotic indexes, could construct new models to determined relative sensitivity of local indicators species. This information will be especially valuable in light of increased human-caused stream contamination.

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