Site-occupancy modelling: A new approach to assess sensitivity of indicator species

Abstract One of the most challenging aspects of quality indices has been to compile reliable measures of the species’ sensitivity 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 modelled occupancy of oligochaete species from physicochemical variables of Pampean streams; and we described the change in occupancy along the gradient of each explanatory physicochemical variable. 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 were enough abundant to be modeled. In eight species, we obtained a total of 11 different models including physicochemical covariates. Occupancy was explained by conductivity in four species, by dissolved oxygen in three species, and by nutrients in four species. The analysis of phases (resistance, tolerance and extinction) to describe the sensitivity of the species in terms of occupancy, offers a new methodology to understand how the species behave along a stressor gradient. Detailed descriptions of sensitivity of these local species, will helps ecologists to generate more accurate biotic indices.