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Conditions Promoting Invasive Species Expansion

Successful invading species can usually tolerate a wide variety of environmental conditions. Also, species in close association with humans, including rats, house mice, house sparrows, starlings, and pigeons are most successful in invading man-modified habitats.

Certain regions are most vulnerable to introduction of invasive species. For example, not all U.S. states are affected equally by invasive species. Particularly vulnerable are Hawaii and Florida, where a high percentage of terrestrial vertebrates are introduced. The primary feature is geographic isolation: Hawaii is an island archipelago, Florida is a peninsula bounded on 3 sides by water and on 1 side by frost zones. A typical feature of islands and isolated areas is an impoverished native fauna relative to equal size mainland areas. Invasive species were successful on Hawaii because native species did not previously occupy similar niches.

A mild climate also makes areas vulnerable to invasive species. Hawaii and Florida have large tropical or subtropical areas without freezing temperatures. The accidental escape of exotic pets like bulbuls or the introduction of tree frogs from nursery stock would not be a problem in most U.S. regions because of cold climates. In Florida and Hawaii they thrive and spread.

Finally, locations vulnerable to introductions are transportation hubs. Most visitors from Latin America, and many from other regions, enter the U. S. through Miami, and Hawaii is a center for both civilian and military traffic moving throughout the Pacific.