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Under Siege! Americaâ€™s Most Unwanted Invasive Species
The United States is under an economic and ecological siege by alien invaders â€” Americaâ€™s Most Unwanted. More than 6,500 of these harmful non-native species cause more than 100 billion dollars in damage each year to the U.S. economy as the country battles to control the economic, ecological, and health threats these invaders pose. Increased global travel and trade are providing more pathways for both intentional and unintentional introductions of invasive species.
Invasive species affect just about everyone in every State in the country, in urban centers and wilderness areas. And their costs are borne by all of us â€” farmers, ranchers, businesses, and local, State, Tribal, and Federal governments.
The Cost of Invasives
Costly effects of invasives include crop decimation (cactus and gypsy moths), clogging of water facilities (quagga and zebra mussels) and waterways (hydrilla, giant salvinia), wildlife and human disease transmission (West Nile virus, monkeypox, and diseases in some shipsâ€™ ballast water), threats to commercial, native, and farmed fisheries (Asian carp, snakehead fish, sea lamprey, Asian swamp eel, whirling disease, and viral hemorrhagic septicemia), increased fire vulnerability (cheatgrass, brome, and buffelgrass) and adverse effects for ranchers and farmers (leafy spurge and cheatgrass).
Researchers with the USGS Invasive Species Program work on every one of those species mentioned; in fact, our researchers work collaboratively on all significant groups of invasive organisms in terrestrial and aquatic ecosystems in all regions of the United States. Across the Nation, our invasive species experts partner with States, other Federal agencies, businesses, agriculture, and natural resource managers to help solve the problems posed by these invaders.
Key components of invasive species activities include prevention, monitoring and forecasting threats, and control and management of established invaders.
During Invasive Species Awareness Week, we will feature some of Americaâ€™s Most Unwanted each day to highlight the impacts of invasive species to the nationâ€™s Ecosystems and economy.
Burmese pythons are now found across more than a thousand square miles of southern Florida, including all of Everglades National Park and areas to the north such as Big Cypress National Preserve. This snake threatens both the native animals and ecosystems in South Florida because they eat a wide variety of prey (mammals, birds, and alligators), and pose a risk to the ecosystems and the animals that live in them, including many including threatened and endangered species. Scientists do not know exactly how many Burmese pythons are living in Everglades National Park, but they believe at least tens of thousands are there.
USGS Research on Burmese Pythons
Recent USGS research provides initial evidence that pythons may be able to survive in marine and estuarine environments such as bays, inlets and open seas. This study showed that in the lab, hatchling Burmese pythons were able to withstand exposure to saltwater long enough to indicate that the species could potentially expand its range through ocean and estuarine environments. These results raise concerns that the constrictor may invade nearby islands, such as the Florida Keys.
Other recent USGS and partner research has demonstrated that some mammal species have declinedÂ in areas where Burmese pythons are established in Everglades National Park. For example the most severe declines, including a nearly complete disappearance of raccoons, rabbits, and opossums, have occurred in the remote southernmost regions of the park, where pythons have been established the longest. In this area, observations of raccoons dropped 99.3 percent, opossums 98.9 percent, and bobcats 87.5 percent. Marsh and cottontail rabbits, as well as foxes, were not seen at all. These mammal species were common in the park before pythons attained high densities, but research shows that their numbers have dropped dramatically over the same time that the pythons were becoming more abundant.
Ongoing research may provide new tools that could limit python population numbers and help prevent further spread. In the meantime, agencies such as the USGS, National Park Service, Florida Fish and Wildlife Conservation Commission, and others are actively testing and applying control and eradication techniques, including trap development, refinement of visual searching methods, and testing detector dogs for locating pythons.
The invasive brown treesnake on the Pacific island of Guam is the poster child of the ecological and economic havoc an invasive species can cause. There, since the snake first invaded the island sometime right after World War II, mass extinctions of most of the islandâ€™s native birds, mammals, and lizards have occurred, which, in turn, have caused cascading and irreversible ecosystem changes.
For example, the loss of these native vertebrates means they are not available to disperse the seeds that pollinate trees and flowers. Consequently, some of the islandâ€™s native trees have greatly declined in abundance and may disappear. Similarly, as fish-eating birds have been lost from Guam by being eaten by the snakes, the natural nitrogen transport from aquatic and marine systems to bird rookeries has been lost as well, adversely affecting the growth of nitrogen-dependent plants on the island.
The Role of an Invasive
â€śMany invasive species take over the role previously occupied by a native species,â€ť said USGS invasive snake expert Gordon Rodda, a scientist with the USGS Fort Collins Science Center. â€śWhile the non-native species might displace that native species, it doesnâ€™t necessarily disrupt ecosystem processes. But when the brown treesnake came to Guam, it occupied a new role as a novel, arboreal night-time predator on birds, lizards, and mammals, a role to which these animals were not adapted.â€ť
The result, said Rodda, is that with the extinction of most of the islandâ€™s vertebrates, the original ecosystem is simply not recoverable. Itâ€™s a cautionary tale for Florida where Burmese python populations are exploding.
Since Guam is overrun with brown treesnakes â€” as many as 13,000 per square mile in some places â€” current efforts focus on preventing them from invading the U.S. mainland or other snake-free islands such as the Northern Mariana Islands, Micronesia, and the Hawaiian Islands. This is challenging because shipping and air traffic from Guam to these other islands is a daily affair and because these snakes are masters at hiding in confined places where they can live a long time without food or water.
Prevention in Paramount
â€śPrevention of spread is paramount,â€ť said Rodda. â€śIt is much cheaper than intervention once a snake population establishes. With prey species that are unused to being hunted by snakes, invading brown treesnakes can remain well-fed with little effort while they continue to multiply. So it is crucial to keep alien species from sensitive environments.â€ť
Without rigorous prevention, said Rodda, it is extremely difficult to control, let alone remove, an introduced reptile species. In the case of the brown treesnake, prevention efforts include working to detect stowaway snakes before they leave the island, as well as extreme vigilance on islands where the snakes are most likely to invade.
A multi-agency Rapid Response Team led by the USGS assists in detecting and capturing brown treesnakes that are found as stowaways or on other Pacific islands after being accidentally transported from Guam. This response team uses USGS research to help them improve their chances of finding snakes, as well as predicting the movements of snakes that could have accidentally made it to another island.
â€śIf the brown treesnake gets to any of these other snake-free islands, it will find a veritable banquet of prey animals â€” and the same thing could happen there as happened on Guam,â€ť Rodda noted. â€śItâ€™s essential to get ahead of the curve and implement prevention efforts at the get-go, before an alien species becomes a problem.â€ť
Of Parasites and Brown Treesnakes
As a consequence of being introduced to Guam in the late 1940s, brown treesnakes have been purged of the parasites that typically infect them in their native range, and which likely help keep their population numbers at reasonable levels. This freedom from natural parasitic enemies may help explain at least some of the ecological success of brown treesnakes on Guam.
Researchers at the USGS Western Ecological Research Center along with collaborators in Papua New Guinea, are investigating ways to exploit the natural parasitic and disease enemies of the snake as possible additional management tools for controlling the population on Guam, if not eradicating them altogether. Although much work remains to be done before experimental studies can begin on biocontrol efficacy, the findings of the USGS researchers to date are encouraging, and more exploratory work is on the horizon.
Eradicating this snake on Guam would have tremendous ecosystem, human health, and economic benefits, and would reduce the risk of invasion for other islands and the U.S. mainland.
Days (and Nights) in the Life of a Brown Treesnake Rapid Responder (contains a cool find-the-snake page to demo how difficult it is to see them!)
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