Introductions and Survival of Nonindigenous Species in Freshwater Systems

Human Interaction with Pests

Humans are worldwide spreaders of nonindigenous species. Humans not only spread their own pathogens but also those of wild and domesticated animals and plants (Bates 1956). Many plants and animals that were deliberately and accidentally introduced by humans would not have become established or naturalized if humans had not already changed the environment and stressed the native species before the introductions (Mooney and Drake 1987). Ewel (1986) described the ecology of Southern Florida and how humans changed it. In general, plant and animal populations of Florida once consisted of a population depauperate of species because the climate is tropical, because the climate limits migration and colonization of flora and fauna from northern land masses, and because the surrounding waters isolate Florida and prevent migration from the south. Most introduced nonindigenous species in southern Florida that are now considered nuisance species were present before government agencies gained control of these lands (Ewel 1986). Ecologist are now only beginning to recognize how vulnerable the land is to colonization by nonindigenous species.