Introduction

Only 60 of the 3,000 species of lizards living today attain an adult body mass greater than one kilogram. Although large lizards represent only 2% of all lizard species, they account for 60% of lizard species considered threatened or endangered. Indigenous large lizards are often the predominant vertebrates with respect to biomass in undisturbed environments (Case 1982; Iverson 1979; Dugan 1980; Pianka 1986; Phillips 1995). However, in degraded habitats, populations of these lizards may be severely depleted relative to expected carrying capacity. Biomass estimates of healthy iguana populations often exceed 20kg/ha, an order of magnitude greater than reported for mammalian herbivores. The absence or reduction of these lizards unquestionably alters the ecosystems of which they are a part.

The islands of the West Indies form the principal archipelago of the neotropics. As a result of prolonged geographical isolation, native mammal species on these islands are few, consisting mainly of bats and rodents. Birds, reptiles, and amphibians, however, have undergone significant radiations and comprise the majority of the vertebrate biodiversity of the West Indies. Most of the large islands are densely populated by people and suffer from environmental degradation and the ill effects of introduced species (Case and Bolger 1991). As a result, a significant number of taxa, including many endemics, have disappeared or are on the brink of extinction.

The iguanas of the West Indies (Cyclura and Iguana delicatissima) are among the largest and most impressive members of the family Iguanidae, yet they are also the rarest. All taxa are currently protected under the Convention on International Trade in Endangered Species (CITES), with five of 17 forms considered to be Endangered, and eight Critically Endangered, by the World Conservation Union (IUCN 1996). Although exploitation of West Indian iguanas began long ago by native peoples, it was probably not until the arrival of Europeans that iguana populations began their most precipitous decline. In addition to the habitat loss and degradation inevitably resulting from large scale human settlement, the commensal species that accompanied immigrants to the islands have had a devastating impact on iguanas and the ecosystems they inhabit. Dogs, cats, pigs, and rats prey on iguanas and their eggs, while goats, sheep, cattle, and other livestock have contributed to the deterioration of the unique plant communities on which iguanas and other native species depend. The introduction of the Indian mongoose (Herpestes javanicus [=auropunctatus]), ostensibly to control rats, has instead resulted in predation of untold numbers of native species, including juvenile iguanas.

Typical dry tropical forest habitat for iguanas at Guantánamo Bay, Cuba.

West Indian iguanas inhabit dry subtropical thorn forest regions in the Bahamas, the Virgin Islands, and the Greater and Lesser Antilles. While Cyclura are terrestrial, depending heavily on the presence of rocky crevices to serve as retreats, Iguana delicatissima is primarily arboreal. Both require sandy areas with appropriate soil conditions in which to lay their eggs. Most species live for multiple decades and may take several years to reach sexual maturity. Social organization ranges from systems in which adult males are highly aggressive and territorial to large groups which appear to coexist peacefully. Mating is seasonal, with a single clutch per year, usually laid in May or June. Raptors, cuckoos, herons, and colubrid and boid snakes are the only natural predators of West Indian iguanas, and then usually only of juveniles.

West Indian iguanas are almost exclusively herbivorous, consuming an unappreciated diversity of vegetation types. The Turks and Caicos iguana is known to feed on at least 58 plant species (Iverson 1979; Auffenberg, 1982), the Cuban iguana on 25 species (Perera 1985a), the Grand Cayman iguana on 45 species (Burton and Gould, in preparation), the Lesser Caymans iguana on over 40 species (G. Gerber, unpublished data), and the Mona Island iguana on 71 species (Wiewandt 1977). Because these lizards do not chew appreciably (Throckmorton 1976), and digestion of plant foods is incomplete, seeds passing through the digestive tract are probably still capable of germinating (Iverson 1985; F. Burton and S. Gould, unpublished data). For this reason, West Indian iguanas are likely to be important seed dispersers for many endemic plants.

The sections that follow are designed to provide a broad historical context for the specific conservation activities recommended later in the Action Plan. Taxonomic issues relevant to West Indian iguanas are discussed, including the need for further phylogenetic studies to help establish conservation priorities. Effects of climate change, ecosystem-level processes, and past and modern human disturbance are covered as well. Finally, an overview of the current status of West Indian iguanas is provided, together with a summary of existing threats and conservation measures for each taxon.