Characterizing the niches of two very similar Nitzschia species and implications for ecological assessment

Abstract

The distributions of Nitzschia inconspicua Grunow and N. soratensis E. Morales & Viz in response to environmental variables were compared using a dataset composed of samples from 46 locations in UK streams and rivers; they were also investigated using laboratory experiments. There were only three samples in which both species occurred with a relative abundance>1%. Nitzschia soratensis preferred water of lower alkalinity, conductivity, reactive phosphorus and total oxidized nitrogen. The different preferences for conductivity of the two species were consistent with the results of the laboratory experiments, although no difference in response to phosphorus was observed in these trials. Interpretation of field results was confounded by correlations among environmental variables. However, taken together with the laboratory experiments, the data suggest that N. inconspicua and N. soratensis are separated primarily by local geology and habitat rather than by human pressures. Discrepancies between the results from laboratory experiments and observed distributions in the field underline the need for caution in using the latter alone for characterizing the realized niche of species for ecological assessment.