Introductions and Survival of
Nonindigenous Species in
Freshwater Systems

Problems from nonindigenous species are probably more serious in Florida than elsewhere in the United States. Special features of the state, such as the subtropical climate, the major ports of entry for nonindige nous species, the burgeoning pet trade, the expanding tropical fish and ornamental-plant industries, the high rates of human immigration, the increasing urbanization, and the extensive environmental manipulations have contributed greatly to this problem (United States Congress 1993). Florida is famous for its mild climate, abundant waterways, beaches, and natural attractions and for its versatility for freshwater and commercial fishing and wildlife habitat (Johnson and Montalbano 1984). Southern Florida, consisting of approximately 9,065 km2, is the part of the state with most of the nonindigenous species and is one of the largest complexes of preserved ecosystems in the eastern United States--including Everglades National Park, the Cypress National Preserve, the Loxahatchee National Wildlife Refuge, and the Fakahatchee Strand Preserve.

Florida is infested with approximately 925 aggressive, nonindigenous plants--most of which were deliberately introduced (Doren and Whiteaker 1991). Many taxonomic classes in Florida contain at least one nonindigenous species. More specifically, the state of Florida lays claim to 63 percent of the nonindigenous bird species (American Ornithologists Union 1983), the largest number of established nonindigenous amphibian and reptilian species (Wilson and Porras 1983), and 25% of nonindigenous plants and land mammals. Overall, approximately 15% of Florida's flora, 16% of its fishes, 42% of its reptiles, 22% of its amphibians, 23% of its mammals, and 5% of its birds are naturalized nonindigenous species (Ewel 1986).

Because of their negative impacts on fishing and water sports, degradation of wildlife habitat, reduction of biological diversity, and alteration of natural ecosystems, some nonindigenous species cause severe problems for the ecology, economy, and resource management in the state. Persisting immigrations of insects and plant pathogens (Frank and McCoy 1992) and continuing range expansion of already established nonindigenous species are anticipated to harm agriculture, natural resources, and human health (Myers and Ewel 1990). Neill (1957) discussed the historical biogeography of Florida.

Disturbed areas such as construction sites, abandoned farm land, drained or stressed wetlands, roadsides, and canals and ditches are most notable where nonindigenous species often displace indigenous forms, alter ecosystem dynamics, and eventually become established. Whether nonindigenous species established themselves by outcompeting and displacing indigenous species in disturbed and undisturbed areas or in mainly colonized disturbed habitats that are no longer primary sites for indigenous species is debated. Colonization of undisturbed areas is typically difficult for many nonindigenous species, but this is inconsequential because most areas of Florida are disturbed to some extent (Ewel 1986; Myers and Ewel 1990). Gleason (1984) discussed the environments of southern Florida in relation to urbanization.

Other conditions such as Florida's subtropical climate and lengthy growing season, plentiful freshwater resources, numerous plant and fish industries, large pet trade, international ports of entry, and ever-expanding tourist industry facilitate the introduction and establishment of nonindigenous species (Shafland 1991). Davis (1943) discussed the natural features of Florida in relation to the vegetation of the state.