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Caught in the Act:Green Iguanas Colonize Caribbean Islandby Donald L. Blanchard |
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This article was originally published in The Cold Blooded News, the newsletter of the Colorado Herpetological Society, Vol 26, #1, January, 1999. Ever since Charles Darwin discovered Iguanas on the isolated Galapagos Islands, scientists have postulated that non-flying land animals could be dispersed by storm-borne "rafts" of debris transported from the mainland or other islands. The possibility of such an event occurring, however, has always been speculative, and has remained controversial. It has been debated whether a breeding colony of terrestrial vertebrates (or a lone pregnant female) could be transported in such a manner and survive to reproduce in their new home. Various animals have been observed on flotsam rafts in the past, but most are smaller creatures like insects; the few land vertebrates observed have been isolated individuals, and it has been questioned whether larger vertebrates could possibly be dispersed in such a manner. Now, as reported in the October 8th issue of Nature, such an event has actually been observed and documented. The summer of 1995 was a busy time for hurricanes in the western Atlantic and the Caribbean Sea. Eleven hurricanes and eight tropical storms were reported that year. On September 4th and 5th, category 4 hurricane Luis swept through the Lesser Antilles islands on the eastern margin of the Caribbean Sea. Gale force winds were reported as far south as the island of Guadeloupe. Then, on September 14th to 17th, category 2 hurricane Marilyn blew through, following approximately the same track (north-westerly), but slightly farther south and west. The West Indian iguana, Iguana delicatissima, is found on most of the islands of the Lesser Antilles, but the green iguana, Iguana iguana, is only found on the more southerly islands, as far north as Guadeloupe. But, in October of 1995, about a month after the hurricanes, green iguanas arrived on the island of Anguilla, over 150 miles farther north. They arrived on a large raft of logs and uprooted trees, some over 30 feet long. At least fifteen individuals were sighted, not including the 3 individuals seen on Scrub Island, about 1/3 mile farther north. Other iguanas were also sighted on the island of Barbuda, nearly 100 miles to the southeast. Field studies commenced within a month of the sightings. Seven individuals, 3 of them males, were captured, marked, and released. One female captured in March of 1998 was found to have enlarged ovarian follicles, and possibly oviductal eggs, indicating that successful breeding of the colonial iguanas is a real possibility. The likelihood that a new species will be successfully established in a new territory like an island is dependent on the probability of animals of both sexes reaching the island at essentially the same time, and the probability of their survival to have an opportunity to breed. The fact that both male and female iguanas reached Anguilla and survived indicates a high likelihood that the island now has a new "native" species. References:
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