The Ecology of Colonization as Seen in the Zoogeography of Anoline Lizards on Small Islands.

Abstract

One group of lizards-the iguanid genus Anolis in the West Indies-is now sufficiently well known to permit an empirical test of ecological theories of colonization in terms of these relatively slowly colonizing forms. Investigation of one special aspect-recent colonization of small distant islands-leads to the following conclusions: (1) Succesfully colonizing species are a small and specialized fraction of the number available for colonization. (2) They are "versatile" species-creatures of the ecotone, physiologically and ecologically tolerant of many conditions and requiring of few. (3) Below some critical island size a colonizing species may by ecological release exclude all congeners. In Anolis this size of island is large (e.g., 560 mi2). (4) Coexistence of colonists is possible either if they have been preadapted in sympatry and arrive nearly synchronously, or if the adaptations for coexistence are evolved in situ on complex island banks. (5) Some species have been modified by failed invasions. (6) Coexistence or exclusion, once achieved, is stable unless there is significant environmental change. (7) Exclusion is a very common phenomenon of low visibility. Coexistence is a less frequent but highly visible phenomenon.