Uncertainties in biotic indicators and a corrigendum to Ponader et al. (2007): Implications for biomonitoring

Many bioindicators based on species composition have been proposed during the past 30 years in both terrestrial and freshwater ecosystems. Kelly (2011) raised the need to better communicate the usefulness and meaning of the indices and their uncertainties. A survey of European bioindicators of freshwater ecosystems has recently highlighted that most indices have not even considered uncertainties. While recording errors have sometimes been taken into account into the calculation of index uncertainties, the reliability of biotic indices in terms of causality and predictability between a given environmental pressure and bioindicator response have seldom been considered. This has led to serious misunderstanding of what bioindicators may be able to achieve. Here a correction to Ponader et al. (2007) is presented showing that the tolerance (ecological niche) of individual species of diatoms along nutrient enrichment gradients is much wider than formerly presented. The correction, together with the comments by Kelly (2011) and recent whole ecosystem experiments seriously question the reliability of diatoms as nutrient indicators, similarly to recent findings with aquatic macrophytes. A more mechanistic basis for biomonitoring is needed based on current ecological science, rather than early 20th century community ecology.