GRAY SQUIRREL:

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]

GRAY SQUIRREL:

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. The grays have also caused severe damage to European forests by stripping trees of their bark, which could potentially impact nesting bird species.  [Less] [Link to this slide]

©SANDRO BERTOLINO

ZEBRA MUSSELS:

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]

ZEBRA MUSSELS:

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. The zebra mussels significantly alter ecosystems by vastly reducing the amount of phytoplankton in the water.  [Less] [Link to this slide]

©AMY BENSON

MOUFLON SHEEP:

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]

MOUFLON SHEEP:

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.  [Less] [Link to this slide]

©ROBERT STEPHENS

REINDEER:

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]

REINDEER:

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.  [Less] [Link to this slide]

©ANDREW RANKIN

FERAL PIGS:

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....[More]

FERAL PIGS:

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.  [Less] [Link to this slide]

COURTESY OF ENVIRONMENTAL PROTECTION AGENCY, QUEENSLAND

CANE TOAD:

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. ...[More]

CANE TOAD:

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.  [Less] [Link to this slide]

COURTESY OF ENVIRONMENTAL PROTECTION AGENCY, QUEENSLAND

MICROBES:

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]

MICROBES:

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. Phytophthora cinnamomi may push these rare trees to extinction in that nation.  [Less] [Link to this slide]

©MIKE WINGFIELD