Prediction of taxon occurrence: a test on taxon-specific change point values of stream benthic invertebrates.

Ecological thresholds represent abrupt species responses to minor changes in the environment. However, as aquatic organisms are frequently exposed to multiple stressors, prediction of taxon occurrence is challenging and often associated with much uncertainty. In this study, we analysed the response of stream benthic invertebrates to selected environmental gradients and determined the frequency and predictability of threshold responses., Re-analysis of taxon-specific change point values for 213 riverine benthic invertebrate taxa and nine water quality variables showed that the predictive performance was acceptable for 30.4% and excellent for 9.6% of the total number of validated change points ( n = 978). In total, 48.3% of the taxa that were predicted to occur (taxon presence predicted) and 67% of the taxa predicted not to occur (taxon absence predicted) were correct but with high variability across taxa and chemical variables. Predictive performance was the highest for stenoecious taxa and for certain chemical variables, such as ammonium nitrogen and the daytime dissolved oxygen concentration., Responses to peak level concentrations of water quality variables were less threshold-like compared with relationships with mean values. However, model predictions were equal for both of the approaches., Successful prediction of taxon absence at stress levels beyond the change point values showed that the latter can well represent the upper limit of the taxon-specific range of occurrence. Thus, change points are valuable for establishing and evaluating new water management tools, such as water quality criteria. By contrast, prediction of taxon presence at low levels of stress was associated with relatively high uncertainty, reflecting the limitation of taxon occurrence by stressors other than those investigated. [ABSTRACT FROM AUTHOR]