Introductions and Survival of Nonindigenous Species in Freshwater Systems

Subtropical Climate

Most of Florida--from the panhandle to Lake Okeechobee--is a continuously hot, humid subtropical climatic zone, and the rest of the state may be described as the only tropical savanna--the Everglades--in the United States (Council of Environmental Quality 1989). The climate in the Everglades alternates between wet and dry seasons. Florida's maximum average temperature range is between 17.2 and 27.8ø C (Winsberg 1990). The lower winter temperatures of northern Florida and especially of south-central Florida (4.4ø C and lower) probably limited the dispersal of many nonindigenous species (Shafland and Pestrak 1982; Wilson and Porras 1983). However, with an average rainfall of 135 cms, Florida is one of the wettest states and thereby favors establishment of tropical nonindigenous species. Because Florida is close to the equator and the weather is tempered by large bodies of water that surround the peninsula, this subtropical climate not only appeals to tourists but provides the necessary climate for industries in the ornamental and aquarium plant trade (United States Congress 1993). Furthermore, Florida is subject to many tropical weather storms that disturb the system and aid the spread of nonindigenous species (e.g., Hurricane Andrew in 1992).