FORT > Resources > Education > BTS Home Page > Invasion of a Predator > Introduced Predators
Introduced Predators on Formerly Snake-Free Oceanic Islands
Due to their inability to cross large stretches of ocean, amphibians, large reptiles, and nonvolant terrestrial mammals are naturally absent from oceanic islands. The species of birds, bats, and small lizards that do reach oceanic islands often develop "island tameness," which is a lack of wariness towards humans and other predators. Numerous examples exist of unwary island species suffering catastrophic population declines when humans bring themselves and other generalist predators to a previously undisturbed island. This is evidenced on Guam by extinctions that occurred both when early humans first entered the scene and with the introduction of the brown Treesnake. Nearly all species of Guam's native wildlife have suffered, including reptiles, birds, and mammals. At present, Guam has lost all breeding populations of seabirds, 10 of 13 species of native forest birds, 2 of 3 native mammals, and 6 of 10 to 12 species of native lizards. Are these types of losses likely in other cases of predator introduction including snakes and other species?
Sadly,
this scenario has been repeated many times in both ancient and recent
human history. Because oceanic-island species often exhibit a complex
of vulnerabilities, they are easy prey for introduced predators.
A second example of a predator introduced for anticipated pest control
is the mongoose. These introductions have often been largely unintentional
or informal, but have frequently been instigated to control rats and snakes.
Introduction of the mongoose to control snakes was tested in the Ryukyu
Islands of Japan but met with little success. Few snakes are eaten
more than opportunistically by these predators, but many nontarget wildlife
species and more preferred menu items such as native lizards have suffered
greatly. In the Caribbean, mongoose were introduced for rat control,
but again the rats continue to proliferate while nontarget species suffer.
Other introduced species that have caused major ecological damage across
the world include invasive terrestrial plants, such as kudzu and purple
loosestrife; toads, such as Bufo marinus; cats and goats, introduced
for rat control and agriculture, that quickly gained the designation of
"feral" in their new environments; and everything in-between.
The impacts of these introduced species, and particularly the brown Treesnake, are so severe that they have been compared to and found to have more lasting effects on the ecological diversity of an island ecosystem than did the naval bombardment and leveling of forests that occurred on Guam during World War II. The war wiped out large tracts of land that were able to recover once the fighting ended. But once an introduced species has eliminated a native, time can offer no chance for recovery.
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