The view is proposed that introduction of
exotic species has considerable merit providing
it results in a reasonably harmonious resource-
portioning with native species. Interactions in
nature are of course difficult to anticipate with
invariable accuracy, but can be predicted with
reasonable reliability. The potential for man-
guided diversification is tremendous and if
exploited intelligently would result in a much
larger portion of successes than failures. The
unoccupied niches that exist for co-existence of
species in tropical, subtropical, and warm
temperate areas, as in southern United States,
where access by potential inhabitants has been
severely limited by natural barriers, are certainly
numerous but very crudely understood. Hasty
attempts to fill some of them could be disastrous,
but careful appraisal with the broadest possible
perspectives could lead gradually to a very
satisfying enrichment yielding important
information on many evolutionary processes
and providing ready access to a wide variety of
materials for laboratory and field study.
Utilization of resources that already exist and
are available for betterment of the environment,
not only for man but for a more richly diverse
biota than already exists, has scarcely been
touched.
More reptiles have been introduced into Florida than into any other state (Ashton and Ashton 1991; Table 8). Reptiles were introduced accidentally on agricultural products and intentionally to help control pests and to augment the pet trade. Many pet traders also illegally transport species into Florida and release them to avoid prosecution for possession of an illegally imported animal. Pet dealers may even release exotics simply to rid themselves of an unprofitable species. Most nonindigenous reptiles are restricted to the Miami area in Dade County (Ashton and Ashton 1991). The most frequent problem from exotic amphibians and reptiles is the replacement of native species because of competition. The most notable example is the giant toad (Bufo marinus) that is replacing the native southern toad (Bufo terrestris) in the cities of southern Florida; the Bahamian bark anole (Anolis distichus), green bark anole (A. d. distichus), Bahamian ground anole (
Marine Toad (Bufo marinus). The native range of the giant toad extends from southern Texas through Mexico and Central America to Brazil in South America. Currently, the marine toad is widespread, occurring outside its natural range in such varied places as Australia, Fiji, Guam, Hawaii, Japan, New Guinea, the Philippines, Solomon Islands, Tonga, several islands in the West Indies, and southern Florida (Wilson and Porras 1983). It was initially introduced as a biological control agent of native pests such as insects and snails and became established throughout most of the tropical regions of the world (Krakauer 1970). In 1936, the Agricultural Experimental Station of the University of Florida imported 200 marine toads from Puerto Rico and released them at Canal Point and Belle Glade in Palm Beach County to control sugar cane (Saccharum officianarum) pests; but the toads disappeared in less than 1 year (Kratzauer 1968, 1970; Riemer 1958). Around 1944, the United States Sugar Corporation introduced the marine toad at Clewiston, Hendry County, but these animals also did not establish themselves; the introductions of two other species of cold-adapted giant toads also failed (Krakauer 1970). A third unsuccessful attempt to introduce the marine toad in southern Florida occurred at a cane field at Pennsuco, Dade County (Duellman and Schwartz 1958; Reimer 1958;).
The present population originated with the accidental release of approximately 100 individuals before May 1955 by a former importer at the Miami International Airport (King and Krakauer 1966). The population remained for several years in the western part of Miami and was breeding in rock pits south of the airport runways; however, in 1958, a canal was constructed to link the Blue Lagoon with the extensive canal system of southern Florida, and the marine toad began to appear in regions distant from the airport (Krakauer 1968). The marine toad is common in many urban and agricultural areas in southeastern Florida and is present on the fringes of the Everglades (e.g., the vicinity of the Chekika State Recreation Area west of Florida City and near the junction of the Tamaiami Trail and U.S. 27; Wilson & Porras 1983). Krakauer (1968) first reported the giant toad from Palm Beach County. The toad was also recorded as established on Stock Island near Key West. Currently it occurs from Homestead in southern Dade County north to Broward County. An isolated population that was probably transplanted is also established in West Palm Beach, Palm Beach County. Animal dealers have deliberately released this species in 1963 at Pembroke Park, Broward County, and in 1964 at Kendall, Dade County (Duellman et al. 1958). Crowe and Stevenson (1992) discovered the giant toad on July 1991 in Dade City, Pasco County. Specimens have been found as far north as Ocala (R.E. Ashton, Vertebrate Ecologist, Water and Air Research, Inc., Gainesville, Florida, personal communication). The marine toad is absent from the wet savanna (Everglades) west of the coastal ridge (Krakauer 1968). It is limited by the Atlantic Ocean to the east and by the Everglades to the west (Krakauer 1968). The distribution of this species is also limited by low temperatures and scarcity of habitat (Krakauer 1968). It is most frequent in disturbed areas, where it occupies two distinct habitats, areas around buildings and suburban backyards and the shores of canals and ponds. The marine toads are most frequently seen under the street lights of the suburbs.
Physiologically, the marine toad is aquatic because its eggs are laid in temporary pools and in roadside ditches. A large female lays more than 5,000 eggs at a single laying. One observer claimed that a single female laid a total of 32,000 eggs (Krakauer 1970). The marine toad's large fertility obviously contributes greatly to this species' ability to expand so rapidly. Although they have mature eggs and seem to be ready to spawn throughout the year, low temperatures and scarce rainfall inhibit breeding in winter (Krakauer 1968). In November 1965, the toad population increased to a point that it was declared a public nuisance and a Dade County official proposed that a bounty be placed on the toad (Krakauer 1968). Krakauer (1968,1970) predicted that the marine toad will extend its population northward along the coast of Florida because of warm temperatures and protection from cold around houses.
In 1968, King stated that the marine toad is replacing the native southern toad Bufo terrestris in residential areas. Because they could not adapt to anthropogenic changes, populations of southern toads declined and were replaced by marine toads (Wilson and Porras 1983). The expansion of the Miami metropolitan area is simultaneously destroying the preferred habitats of the southern toad but creating new habitat for the marine toad; therefore, the marine toad continues to prevail in its present range (Krakauer 1968).
Marine toads have voracious appetites and eat any small, moving or non-moving objects such as insects, snails, snakes, garbage, and dog food (Alexander 1964; Krakauer 1968). Any resident of southern Florida can give at least one account of seeing a marine toad eat from a pet's food bowl. If bitten, the toads release milky bufotoxin from the parotoid glands that makes pets ill; however, cats and dogs learn to avoid this noxious species after only one encounter (Ashton and Ashton 1988). Although wildlife in southern Florida usually does not prey on this species, Garrett and Boyer (1993) saw an opossum Didelphis marsupialis attack and possibly eat this toad even after it had a reaction to the bufotoxin. However, Ashton and Ashton (1988) believe that the marine toad is harmless and makes a good pet.
Many people buy the giant marine toads and release them in their back yards to control garden insects and slugs and have thus increased the rapid range expansion of the species and possibly the creation of the satellite populations in Palm Beach and Monroe counties. Accordingly, some people feel that the toads are useful predators and valuable additions to the local fauna (Krakauer 1970). However, the marine toad is suspected of preying heavily on native toads and on other small organisms--but investigations of the effect of the marine toad on native fauna have yet to be implemented.
Cuban Treefrog (Osteopilus septentrionalis). The Cuban treefrog is an immigrant from the West Indies and is one of the largest of the eastern and central American treefrogs (Conant and Collins 1991). During the nineteenth century, it probably arrived in the Florida Keys in a ship's cargo and expanded its range in southern Florida (Ashton and Ashton 1988). It has been recorded along the Atlantic Ocean from Dade to Indian River counties and on the west coast from Monroe to Sarasota counties. It was first reported in Key West by Barbour (1931), since then dispersed northward (Austin 1975), and was reported on the Upper Matacumbe Key by Trapido (1947), in Key Largo by Allen and Neill (1953), in Miami by Schwartz (1952), in Dania by King (1960), on the Broward-Palm Beach County line by Lee (1969), in Palm Beach County by Austin (1975), and in Saint Lucie and Indian River counties by Myers (1977). This species has also been reported on the western coast in Naples by Duellman and Crombie (1970), and Wilson and Porras (1983) reported it from Fort Myers, Sanibel Island, and Fort Myers Beach. Somma and Crawford (1993) discovered the Cuban treefrog in Pinellas County and noted its occurrence in Glades County. Wilson and Porras (1983) speculated that this species arrived in southern Florida by rafting.
The Cuban treefrog is aquatic because it lays its eggs in rain pools, temporary ponds, and ditches. This species is so flexible that it can live in the suburbs and in rural areas such as pinelands and mesic-tropical hammocks (Ashton and Ashton 1988). Because it preys on local insects and other treefrogs, it may be considerably harmful to the native treefrogs of Florida (Ashton and Ashton 1988). However, the knight anole (Anolis equestris) preys on this species (Wilson and Porras 1983).
Common Caiman (Caiman crocodilus). The number of imported common caimans in the United States for primarily the pet industry increased drastically because the American alligator (Alligator mississippiensis) was protected from trading in the early 1950's (Moore 1954). Common caimans are natives of Central and South America and were probably introduced for the pet trade throughout Florida and other gulf states (Smith and Kohler 1978). The U.S. Fish and Wildlife Service reported 112,402 individuals that entered the United States through the Miami port-of-entry during 1970 (King 1974).
Presently, common caimans are breeding in the canals of the Miami area; more specifically, in the late 1950's Louis Pourra observed several caimans of various sizes in a section of a canal that extended from Maule Lake to N.W. 27th Avenue, and Ellis (1980) reported the presence of common caimans in canals in Miami as early as 1960. In 1968, a local collector brought common caimans from a canal in North Miami, around N.W. 22nd Avenue and 197th Street, into the animal trade. The collector reported the presence of nests in that area (Wilson and Porras 1983). An adult common caiman with several young on its back was spotted in 1976 and in 1980 near Coopertown on the Tamiami Trail (Wilson and Porras 1983). Ellis (1980) reported an established and breeding population confined to the canal system on the Homestead Air Force Base; the population was first discovered in 1974. Most of these populations are restricted to drainage canals less than 50 m from the main housing area and within 10 m of a constantly traveled concourse.
After its introduction into open waters, the common caiman increased so drastically that in 1977 extirpation began with the sanctions of the state of Florida and the federal government (Ellis 1980). Although extensive efforts have been made to extirpate the caiman populations in Homestead, frequent sightings in other areas suggest that more intensive efforts are needed to substantially arrest permanent populations in Florida (Ellis 1980). Efforts to extirpate these populations have not been successful (Wilson and Porras 1983).
Red Eared Turtle (Tachemys scripta elegans). This turtle is a variety of the slider (Pseudemys scripta) and occupies the Mississippi Valley from Illinois to the Gulf of Mexico (Ernst and Barbour 1972). Ashton and Ashton (1991) noted that it is one of the most popular turtles in the pet trade. It is not indigenous to southern Florida. Since 1958, breeding individuals have been reported throughout canals in metropolitan Dade County and in Collier, Duval, Marion, and Orange counties (Ashton and Ashton 1991). Populations are also in the Swannee drainage and near High Springs (R.E. Ashton, Vertebrate Ecologist, Air and Water Research, Inc., Gainesville, Florida, personal communication). Hutchison (1992) noted a viable population in the Fox Hall Pond on Eckerd College in Pinellas County. As human development continues, the southern populations of the red eared turtle may expand their range and eventually join the northern populations (Hutchison 1992).
