Using local-regional richness plots to test for species saturation: Pitfalls and potentials

  • Srivastava D
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0[ Plots of local versus regional species richness are an exciting new tool for testing for species saturation in ecological communities[ In this method\ the local richness of a community is plotted as a function of its regional richness for di}erent biogeographical regions[Aproportional relationship between local and regional richness is interpreted as evidence for an unsaturated community\ that is\ a community with strong evol! utionary limits to local richness[ There will be no correlation between local and regional richness in a saturated community\ that is\ a community whose local species richness is limited largely by ecological processes[ 1[ Although at least 25 data sets have now been analysed using localÐregional richness plots\ there has not been much critical evaluation of the method[ This paper provides such a critique\ focusing on the selection of communities for comparison\ the preva! lence of pseudoreplication and multiple null models\ and the e}ects of di}ering region size[ 2[ LocalÐregional richness plots are best suited for comparing similar habitats between di}erent regions\ not di}erent habitats in a single region[ In the latter\ taxa e}ects and species pool e}ects are confounded[ 3[ Four very di}erent types of localÐregional richness plots have been published[ Each type of plot has important underlying assumptions which are often not addressed by ecologists[ 4[ Of the 25 data sets reviewed in this paper\ 02 were spatially pseudoreplicated\ and 1 were temporally pseudoreplicated[ Furthermore\ ecologists di}er in their choice of null model\ with the result that the same localÐregional plot could be interpreted as evidence for saturation by one ecologist\ and for lack of saturation by another[ 5[ Di}erences in region size can result in pseudosaturation\ the appearance of satu! ration by an unsaturated community[Asimple model demonstrates this phenomenon[ Other sources of error in estimating the regional species pool are also of concern[ 6[ In conclusion\ localÐregional richness plots are a potentially useful tool for dis! tinguishing saturated from unsaturated communities\ but should be used cautiously\ and in conjunction with other supporting evidence "such as the presence or absence of competitive exclusion\ resource limitation\ density compensation and the e}ects of species invasions

Author-supplied keywords

  • Pseudoreplication
  • Region size
  • Species pool
  • Species richness
  • Unsaturated communities

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  • Diane S. Srivastava

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