Biogeography of the Puerto Rican Bank: Introduction of Species onto Palominitos Island

Frogs, snails, and a rainforest Drosophila introduced to a small sandy cay became locally extinct almost immediately, probably because microhabitats suitable for avoiding the extremes of physical environnemt were lacking. Two introduced species of lizards and one ant species, all three of which have been known from habitats similar to that of Palominitos, survived for from several weeks to about 1 year. Their eventual extinction was probably due to biotic factors: absence of a suitable habitat in which the introduced species had an advantage over its native competitors, predation (between lizard species), and a general advantage of established populations (mature ant colonies, lizards with territories) over an immigrant propagule. An argument is presented that if the rigors of the physical habitat reduced life expectancy by less that 60% below that of a species' optimum habitat this will not be sufficient to prevent its establishment, but a reduction of over 90% is almost certainly enough to exclude it.