The theory of island biogeography was tested in Nicaraguan volcanic crater lakes, colonized by fish from the older and larger source Nicaraguan Great Lakes. Spearman correlations of ranked molecular phylogenetic diversity in the Midas cichlid species complex (Amphilophus cf. citrinellus) were significant (p ≤ 0.05) or marginally significant (0.05 < p ≤ 0.10) with diversity with crater lake age in three of four data sets tested. Correlations were noted with deepwater area, the product of littoral area and age, and with the product of horizontal and vertical barriers between the crater lakes and the nearest source lakes divided by the product of littoral area and age. By treating the Midas cichlid species complex as a single taxon, ranked fish taxon richness in each lake correlated significantly with lake age, littoral area, and with the product of age and littoral area. These results support the concept that littoral area and lake age may be factors in the colonization of volcanic crater lakes from the source lakes, and the amount of deep water in a lake as well as lake age may be important factors in speciation in the Midas cichlid species complex. Seven species from the crater lakes have been classified as Critically Endangered by the IUCN.

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