Declines in amphibian populations have been recognized worldwide over many regions and habitat types (Alford and Richards, 1999). No single cause for declines has been found, although acid precipitation, environmental contaminants, the introduction of exotic predators, disease agents, parasites, and the effects of ultraviolet radiation have been suggested. In fact, several factors may interact in such a manner as to threaten populations (Carey and Bryant 1995). A major factor in the loss of amphibian and reptile populations has been and continues to be the loss of habitat.

In response to concerns about the lack of basic knowledge of the amphibians and reptiles inhabiting Department of Interior (DOI) lands, inventory programs are being instituted nationwide. The Center for Water and Restoration Studies of the U.S. Geological Survey is conducting a reptile and amphibian inventory of Biscayne National Park (BISC) in cooperation with the Florida Cooperative Fish and Wildlife Research Unit. BISC is primarily an aquatic park with small islands and spans over 173,000 acres.

We have established 16 permanent inventory sites that are sampled on a monthly basis in BISC. During each sampling occasion, a 20m radius circular plot is searched using standard visual encounter survey (VES) techniques, and a 10-minute vocalization survey is conducted to detect calling anurans (frogs and toads). The locations of these sites were chosen randomly within habitat strata. Four of these sites (two in scrub habitat and two in mangrove habitat) are on the mainland portion of the park. Eight monthly sampled sites (three in scrub habitat, two in prairie habitat, and three in mangrove habitat) are on Elliott Key, the largest island in BISC. Two monthly sites (one in mangrove habitat and one in hammock) exist on both Sands Key and Boca Chita Key. In addition to the 16 monthly sites, we also have conducted surveys at six other random sites. These have all been in scrub and mangrove habitat sites on the mainland and on Elliott Key. Our goal is to continue to add random sites until all habitats on islands and the mainland have been surveyed.

Sampling for amphibians and reptiles in (BISC) began on May 2, 2002. As of November 30, 2002 a total of 22 sites have been surveyed during 76 sampling occasions. A total of 65 individuals of 12 species during VES surveys (table 1) and 7 species of anurans by vocalizations (table 2) have been observed.

Nine amphibian species have been detected in BISC, all anurans. Three of the nine amphibian species are introduced in south Florida: the greenhouse frog (Eleutherodactylus planirostris), the Cuban treefrog (Osteopilus septentrionalis), and the marine toad (Bufo marinus). These species have been detected on the islands and mainland of BISC. Five of the native amphibian species detected, the green treefrog (Hyla cinerea), the squirrel treefrog (Hyla squirrella), the leopard frog (Rana sphenocephala), the Florida cricket frog (Acris gryllus), and the pig frog (Rana grylio) have only been detected in mainland parts of the park. The narrowmouth toad (Gastrophryne carolinensis) is the only native frog detected on the islands to date.

Six species of reptiles, four lizards, and two snakes have been detected. Of the lizards, the brown anole (Anolis sagrei) and the tropical house gecko (Hemidactylus mabouia) are both introduced in south Florida. Tropical house geckoes are especially abundant on the buildings of Elliot Key. The green anole (Anolis carolinensis) and the Florida reef gecko (Sphaerodactylus notatus) are native to south Florida. The two snakes, the ringneck snake (Diadophis punctatus) and the Florida water snake (Nerodia fasciata pictiventris) are both native. Each of these has only been observed once.

Monthly sampling of the 16 permanent plots will continue through July 2003. In addition, random points throughout the park will be sampled. Each of these will be sampled at least twice during the study. We expect the number of species encountered to increase as this study continues, especially the number of reptiles.

Although the final inventory may include many species not encountered to date, the substantial constituency of exotic amphibian and reptiles inventoried in BISC during this study calls for some concern.

REFERENCES

Alford, R.A., and S. J. Richards, 1999, Global amphibian declines: a problem in applied ecology. Ann. Rev. Ecol. Syst. 30:133-165.

Carey, C., and C. J. Bryant, 1995, Possible interrelations among environmental toxicants, amphibian development, and decline of amphibian populations. Environ. Health Perspec. 103 (Suppl. 4):13-17.

Contact: Amber D. Dove, Florida Cooperative Fish and Wildlife Research Unit, Everglades National Park, 40001 SR 9336, Homestead, FL 33034; Phone: 305-242-7800 x7333, email: amber_dove@usgs.gov

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

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