Cuddly Squirrel or Gray Menace?: When Invasive Species Pose an Environmental Threat

Scientists find themselves choosing between animals as explosions of some populations endanger others
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Pathogens—microscopic organisms that cause disease—can spread in a variety of ways, from air travel to shipping. For example, tree diseases that travel via lumber supplies have devastated some native forests, such as the silver trees of Table Mountain south of Cape Town in South Africa.....[ More ]


Introduced to Australia in 1935 to control sugarcane-eating beetles, cane toads failed in that mission and have steadily colonized more and more of the continent. With voracious appetites, they have decimated the populations of their prey and—due to a lethal toxin in their skin—would-be predators, including pygmy freshwater crocodiles, northern quolls and Australian monitor lizards known as large goannas.....[ More ]


Domesticated pigs that return to their wild roots are damaging ecosystems around the world, from small islands to entire continents, like the ones shown here in Australia. In the U.S., feral pigs are rooting up vegetation and competing with native animals for resources in many states, including Texas, Oregon and Hawaii.....[ More ]


Native to the Arctic, reindeer have wreaked havoc on the sub-Antarctic island of South Georgia since their introduction in the early 20th century. And their havoc may spread if retreating glaciers continue to expand the reindeers' potential range.....[ More ]


Humans introduced these cloven-hoofed invaders to the area around the dormant Hawaiian volcano of Mauna Kea in the 1960s. The sheep have adjusted nicely to their new home, with populations steadily increasing, much to the detriment of native flora, including the highly endangered silversword plant.....[ More ]


The invasive mollusks hitchhiked to the Great Lakes in ballast water in the 1980s and now cluster on pipes, boats, buoys and, in the case pictured here, on a Lake Erie mussel, commonly known as a fatmucket.....[ More ]


Since their introduction to the U.K. at the end of the 19th century, these twitchy-nosed invaders have decimated indigenous red squirrels by spreading disease and beating them out for food and other resources.....[ More ]

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