The persistence of Anolis trinitatis as a naturalized lizard in Trinidad against hybridization pressure with Anolis aeneus

Anolis aeneus and A. trinitatis were introduced to Trinidad before 1900, and A. extremus was a more recent introduction in the 1960s-1980s. The three species are of similar body size, and A. aeneus and A. trinitatis are known to hybridize in Trinidad. Detailed studies from the late 1960s indicated that A. aeneus was widespread but A. trinitatis was localized and apparently in decline due to hybridization pressure. In this study we examined all the known sites of A. trinitatis (and A. extremus ) in Trinidad, and many new sites. A. trinitatis remained abundant in and to the east of San Fernando in southern Trinidad. Two small populations remained in northern Trinidad, at one site in Port of Spain and at St Augustine, but A. trinitatis no longer occurred at most former sites there. A. trinitatis and A. aeneus had high niche overlap (0.99 or greater) for the three dimensions examined (substrate type and perch height and diameter). Both species were apparently still spreading into vacant habitats east of San Fernando. Of 12 sites from which A. trinitatis had disappeared, four had no anoles, four had sparse populations of A. aeneus , and only four had dense populations of A. aeneus . This pattern suggests that the decline of A. trinitatis is not related to hybridization with or competition from A. aeneus . An alternative hypothesis is presented, that A. trinitatis requires more vegetated habitats, which have been increasingly lost during urban development especially in northern Trinidad. A. extremus is apparently now extinct in Trinidad.