Community relaxation in fragmented landscapes: the relation between species richness, area and age


  • A. Gonzalez

    1. NERC Centre for Population Biology, Imperial College at Silwood Park, Ascot, Berkshire, SL5 7PY, U.K. and Laboratoire d’Ecologie, Fonctionnement et Evolution des Systèmes Ecologiques, CNRS URA 258, Ecole Normale Supérieure, 46 rue d’Ulm, F-75230 Paris Cedex 05, France.
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Estimates of species loss due to habitat destruction are normally based on calculations employing the species–area relation, S = cAz. The validity of this approach is based on the assumption that the value of the exponent (z) defining the slope of the species–area relation in nonfragmented communities is at a steady state and that z is thus a constant. However, departure from such an assumption renders this approach unreliable. Here I report the results from a natural field experiment using “model” bryophyte-based microlandscapes designed to follow the species richness dynamics of microarthropod communities postfragmentation. Community isolation due to fragmentation initiated a delayed community relaxation process and resulted in substantial local extinction. Over the period of the experiment z declined in the control communities and yet remained fairly stable in the fragmented communities. I conclude that predictions of species loss due to habitat fragmentation that do not take into account the fact that often z may not be a constant may lead to error-prone predictions of future species loss.