St. Croix Ground Lizard
St. Croix Ground Lizard
|Listed||June 3, 1977|
|Description||Small lizard with brown head and stripes its back.|
|Habitat||Beach areas and upland forests of Green Cay.|
|Food||Sand fleas, small white moths, and hermit crabs.|
|Threats||Habitat destruction, predation by the mongoose.|
|Range||U.S. Virgin Islands|
The Ameiva polops, (St. Croix ground lizard) is a small species measuring 2-2.5 in (5.0-6.5 cm). The head is uniform brown dorsally. The dorsal pattern consists of a series of longitudinal stripes, a light brown mid-dorsal stripe followed laterally by a series of other bands, in the order of a wide dark brown or almost black one, a white one, and finally a dark brown one mottled with white. The pupil of the eye has a figure-eight shape, and the iris is a light grayish-brown. A deep pinkish-red is observed on the chin, throat, chest, side of snout and underside of the arms. Under the tail and arms there is a slight tinge of pink. The venter is light gray with lateral bluish markings. The tail is marked with alternate rings of blue and black. Other physical characters which distinguish the species from other Ameivas include: 10 longitudinal rows of ventral scales, 33-39 femoral pores, dorsal caudal scales in oblique rows, enlarged median gular scales, and two parallel rows of pernal scales. Color variation among individuals consists of differences in the prominence and color of the stripes. The Green Cay population of A. polops differs morphologically from the Protestant Cay population in that there is a significantly higher number of preanal scales.
The food items known to be consumed by A. polops species include amphipods (i.e., sand fleas) found in beach debris by individuals foraging in tidal wrack, small white moths taken from under the litter, and hermit crabs (reported for an introduced population, now extirpated, of A. polops on Buck Island. Like most Ameivas, this species is diurnal, when it can be seen foraging for ants and other insects, and occasionally resting and sunning itself in the open.
The literature on A. polops is scant and there are no comprehensive works on its biology. Recent habitat information regarding Green Cay only indicates that the most heavily used habitat are beach areas and upland forest of the Hippomane-Tabebuia woodland, although exclusive use of such habitat was not suggested. Principal plant species in this woodland include the trees Hippomane mancinella, Tabebuia heterophylla, Exostema caribaeum, and the shrubs Eupatorium sinuatum, Lantana involucrata, and Croton betulinus. Green Cay falls in the subtropical dry forest life zone. Upland forests used in Green Cay are seasonally deciduous woodlands. Optimal A. polops sites in Green Cay are characterized by exposed and canopied areas (including trees), leaf or tidal litter, loose substrate, and crab burrows. Differential utilization of habitat among the size classes exists, with smaller individuals being found in more exposed habitat and larger A. polops in canopied sites.
In pristine times, A. polops was probably restricted to St. Croix, U. S. Virgin Islands and its offshore islands and cays. Although the species was thought to have become extinct during the early twentieth century, the species was later rediscovered 100-160 ft (30-50 m) inland on St. Croix, Protestant Cay, and Green Cay. No individuals have been seen on St. Croix proper since 1968. A. polops was introduced on Buck Island but is no longer extant, probably due to mongoose predation. Present known occurrence of the species is restricted to Protestant Cay and Green Cay. Information available does not provide evidence of preferred areas in these cays, suggesting the species is found throughout. Although some evidence indicates heavy use of beach areas and upland forests on Green Cay, there is no indication that the species is restricted to such habitats. Only the population at Green Cay occurs on federally managed land, Green Cay National Wildlife Refuge in the Caribbean. The Cay is given protection by the National Park Service through a cooperative agreement with the U. S. Fish and Wildlife Service.
A. polops is threatened by habitat destruction or modification and to predation pressure by the introduced Indian mongoose (Herpestes auropunctatus). Essential habitat has been lost due to the extensive development of the coastal fringes, but the major cause of extirpation from St. Croix is attributed to predation by the mongoose. The species' present restricted range includes only Green and Protestant Cays. The former is a U.S. National Wildlife Refuge, but the latter houses an active hotel complex. Present threats in Protestant Cay are represented by habitat modification through beautification practices (i.e., constant raking and under-growth removal). The future of A. polops populations will depend on the fate of these cays. Future threats to the species include the danger of accidental invasion of said cays by the mongoose, and the species' vulnerability to natural catastrophes such as hurricanes, primarily because of their small size and reduced habitat area. An increase in human disturbance or habitat alteration at important habitats, resulting from recreational activities, could also be detrimental.
Conservation and Recovery
The following activities are recommended in the Recovery Plan for this species: transplanting wild individuals; controlling and removing exotic vertebrates; controlling and restricting development; continuing protection of population and habitat on Green Cay; and limiting human disturbance on Green Cay. The Green Cay National Wildlife Refuge provides protection for 14 of the 18 acres (7.2 hectares) of designated Critical Habitat for the species.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
Conservation Management Institute. 1 May 1998."Species LIZARD, GROUND, ST. CROIX." Endangered Species Information System. http://fwie.fw.vt.edu/WWW/esis/lists/e154006.html.