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How many freshwater diatoms are pH specialists? A response to

Authors

  • Richard J. Telford,

    Corresponding author
    1. Bjerknes Centre for Climate Research, Allégaten 55, N-5007 Bergen, Norway
    2. EECRG, Department of Biology, University of Bergen, Allégaten 41, N-5007 Bergen, Norway
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  • Vigdis Vandvik,

    1. EECRG, Department of Biology, University of Bergen, Allégaten 41, N-5007 Bergen, Norway
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  • H. J. B. Birks

    1. Bjerknes Centre for Climate Research, Allégaten 55, N-5007 Bergen, Norway
    2. EECRG, Department of Biology, University of Bergen, Allégaten 41, N-5007 Bergen, Norway
    3. Environmental Change Research Centre, University College London, 26 Bedford Way, London WC1H 0AP, UK
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E-mail: richard.telford@bjerknes.uib.no

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.

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