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Keywords:

  • Island biogeography;
  • isolate curves;
  • minimum-area effect;
  • Ockham’s razor;
  • small-island effect;
  • species–area curve;
  • species–area relationship

Abstract

Species–area curves from islands and other isolates often differ in shape from sample-area curves generated from mainlands or sections of isolates (or islands), especially at finer scales. We examine two explanations for this difference: (1) the small-island effect (SIE), which assumes the species–area curve is composed of two distinctly different curve patterns; and (2) a sigmoid or depressed isolate species–area curve with no break-points (in arithmetic space). We argue that the application of Ockham’s razor – the principle that the simplest, most economical explanation for a hypothesis should be accepted over less parsimonious alternatives – leads to the conclusion that the latter explanation is preferable. We hold that there is no reason to assume the ecological factors or patterns that affect the shapes of isolate (or island) curves cause two distinctly different patterns. This assumption is not required for the alternative, namely that these factors cause a single (though depressed) isolate species–area curve with no break-points. We conclude that the theory of the small-island effect, despite its present standing as an accepted general pattern in nature, should be abandoned.