title: How many freshwater diatoms are pH specialists? A response to Pither & Aarssen (2005).
abstract: Pither & Aarssen (2005) propose a null model approach to assess the proportion of niche specialist taxa along ecological gradients. They apply this methodology to a large data set of lacustrine diatom assemblages and conclude that a majority of the taxa are generalists on a pH gradient. This conflicts with previous work, which shows that many diatom taxa have a statistically significant relationship with pH. We demonstrate the methods used by Pither & Aarssen (2005) have a high Type II error for rare taxa, and that this problem is compounded by the non-uniform sampling of the pH gradient which effectively precludes acid-lake specialist diatoms from being recognized as such. We re-analyse the data used by Pither & Aarssen (2005) and show that most of the diatoms have a statistically significant relationship with pH, and we thus refute their conclusions that few diatom species are specialists.
authors.affiliation: Bjerknes Centre for Climate Research, Allégaten 55, N-5007 Bergen, Norway. richard.telford@bjerknes.uib.no
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Telford
authors.forename: Vigdis
authors.initials: V
authors.lastname: Vandvik
authors.forename: H J B
authors.initials: HJ
authors.lastname: Birks
mesh_terms: D000222:Adaptation, Physiological; D002965:Classification; D017377:Diatoms / Q000145:classification* / Q000502:physiology*; D004463:Ecology; D006863:Hydrogen-Ion Concentration; D011157:Population Dynamics; D015203:Reproducibility of Results