Island bird richness scales as a power of area
Supplied working report; original verdicts not validated.
Review status: Needs review. This is an archival source note, not a passed proof.
notes.md
# Island bird richness scales as a power of area **Verdict: Partly supported.** The area exponent is 0.11 (95% CI 0.07 to 0.14) and the power form explains 63% of the variance in log richness, but the exponent is at the low end of the island-bird range and collapses to 0.03 (95% CI -0.02 to 0.08) once GBIF record volume is controlled, so the area effect is largely shared with collection effort. ## Design Cross-section of 38 island states with no land borders: bird species counted in a rarefied sample of 1500 GBIF occurrence records per country, against World Bank land area (2022). OLS of log10 species on log10 area, with total GBIF record volume as a control. ## Result - Islands: 38 - Area exponent z: 0.11 - 95% CI: 0.07 to 0.14 - Variance explained: 63% - z with record control: 0.03 ## Limits - Rarefying records does not equalise spatial coverage: a large island is sampled over more of its area than a small one, which can inflate z. - GBIF holds documented, not complete, richness; species described only in literature are absent. - The hypothesis says the exponent is set by the immigration/extinction ratio; a cross-section of one exponent cannot identify that ratio. - Island states differ in latitude, isolation and human modification, all of which shift richness independently of area.