Maintenance of biodiversity on islands

Ryan A. Chisholm, Tak Fung, Deepthi Chimalakonda, James P. O’Dwyer

Research output: Contribution to journalArticlepeer-review


MacArthur and Wilson’s theory of island biogeography predicts that island species richness should increase with island area. This prediction generally holds among large islands, but among small islands species richness often varies independently of island area, producing the so-called ‘small-island effect’ and an overall biphasic species-area relationship (SAR). Here, we develop a unified theory that explains the biphasic island SAR. Our theory’s key postulate is that as island area increases, the total number of immigrants increases faster than niche diversity. A parsimonious mechanistic model approximating these processes reproduces a biphasic SAR and provides excellent fits to 100 archipelago datasets. In the light of our theory, the biphasic island SAR can be interpreted as arising from a transition from a nichestructured regime on small islands to a colonization-extinction balance regime on large islands. The first regime is characteristic of classic deterministic niche theories; the second regime is characteristic of stochastic theories including the theory of island biogeography and neutral theory. The data furthermore confirm our theory’s key prediction that the transition between the two SAR regimes should occur at smaller areas, where immigration is stronger (i.e. for taxa that are better dispersers and for archipelagos that are less isolated).

Original languageEnglish (US)
Article number20160102
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1829
StatePublished - Apr 27 2016


  • Biodiversity
  • Colonization-extinction balance
  • Island biogeography
  • Niche structure
  • Small-island effect

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology
  • General Immunology and Microbiology
  • General Environmental Science
  • General Agricultural and Biological Sciences


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