Colonization of the Lesser Antilles by land birds

Abstract

This study addresses characteristics of source and island populations of nonraptorial land birds that have colonized the Lesser Antilles to determine whether colonization by individual source populations is a continuous process or occurs in transient phases. Species were classed as non-colonists, recent colonists, old endemic residents in the Lesser Antilles, and old endemic taxa that had recently spread within the archipelago. If colonization were transient, source populations of recent colonists would be more widely distributed than source populations of older, endemic island species. I compared the ecological and geographic distributions of source populations and island populations for each of the colonization groups based on a variety of literature and field data. Ages of colonization events and spread within the islands were determined by sequence divergence in mitochondrial genes, where available; relative ages were otherwise inferred from taxonomic differentiation and gaps in island distribution. Within the Lesser Antilles, old colonists, whether endemic or recently spread, tended to inhabit forest rather than open environments. Recently spread old colonists, like young colonists, had relatively greater abundance and broader habitat distribution within islands. These patterns were paralleled in northern South American source populations, but the trends were relatively weak. The strongest pattern was the propensity for source populations of young colonists and older, re-expanded endemics to occur independently on islands off the Caribbean coast of Venezuela. In comparisons with non-colonists in Trinidad, species that have recently colonized the Lesser Antilles tended to occur in more open habitats and to be more abundant locally, as well as more widespread through continental zoogeographical zones. Nested ANOVA based on a taxonomic hierarchy demonstrated that relative abundance and ecological and geographic distributions are labile, most of the variation being among species within genera. This is consistent with the idea that periods of high population productivity leading to colonization of offshore islands are transient. The existence of such phases can be inferred from correlations, albeit weak, between the status of populations in the Lesser Antilles and the ecological and geographic distribution of their putative source populations in the mainland.