Aliens Among Us

Alien space invaders have landed. They're living among us - millions of them - overrunning habitats, driving out other life forms, spreading like wildfire through cities, suburbs, farmlands, and hinterlands. They're often hard to pick out in a crowd, and some­times we don't even know they're aliens.

They aren't extraterrestrial beings that have space-hopped from distant galaxies. They're animals and plants from other parts of Earth that are taking our lands and waters by storm. Also known as "nonnative" and "exotic," they weren't here when the first explorers and settlers arrived in centuries past. Unlike homegrown species, which evolved over mil­lions of years in their own environments, non-native species are strangers here. They're exotic imports, like the Norway rat, Scotch broom, and Asian gypsy moth. Many of them cause massive environmental and eco­nomic harm. The alien invasion is a global threat that is shaking Canada and the world.

Alien species reach new environments in many ways. People usually play a part in their passage - sometimes accidentally, sometimes intentionally. These alien highways and byways include:

• Shipping. The greatest source of invasive species is ballast water taken on ships for stability and later dumped into harbours worldwide. Among the species that have come here this way are the zebra mussel, round goby, and spiny water flea. Other plants and animals arrive as stowaways hidden in cargo on ships, trains, trucks, and planes.
• Canal construction. Artificial waterways have allowed the sea lamprey, an eel-like fish from the Atlantic Ocean, to cross natural barriers and invade the Great Lakes.
• Garbage dumping. Floating human-made rubbish provides mobile homes for marine life, like barna­cles, worms, and molluscs, to cross the ocean to distant shores.
• Recreation. Plants and animals often hitch rides on watercraft, mountain bikes, all-terrain vehi­cles, hiking boots, and fishing gear. The rusty crayfish crossed our southern border via bait buckets dumped in Canadian water.
• Domestic animals. The release of unwanted aquarium pets has introduced red-eared sliders, European wall lizards, and other exotic reptiles into the wild.
• Gardening and agriculture. The escape of culti­vated plants from gardens and croplands to wet­lands, grasslands, and roadsides is a common vehicle for alien invaders, such as purple loose­strife and garlic mustard, which now cover millions of hectares all across Canada.
• Natural pathways. Wind, water, and wildlife can advance the spread of exotic plants and animals.
• Intentional releases. European starlings and house sparrows let loose in New York City's Central Park in the 19th century now blanket the Western Hemisphere. Brown trout and carp intro­duced from Eurasia now flourish in North American waters.

Not all alien species are invasive, and some can have a positive impact. Many introduced species, such as soybeans and wheat, are beneficial. The brown trout and ring-necked pheasant from Eurasia actually boost biological diversity and are prized by Canadian anglers and hunters. Others, such as the Asian long- horned beetle and gypsy moth, have destroyed count­less hectares of timberland. The alien invasion is like a giant eraser that wipes out native animals and plants - the very fabric of the web of life. Its impacts include:

• Habitat loss and degradation. Hundreds of wild boars native to Europe have escaped from game farms in Western Canada, where they dig up grasslands, gardens, and forests in search of tubers, bulbs, and roots and leave a trail of destruction behind.
• Competition with native species. In the battle for food, water, shelter, and space, alien invaders generally strive to oust native species out of their homes. Purple loosestrife from Eurasia takes over wetlands by displacing plants, such as cattails and rushes, and forming impenetrable stands. Competition from Scotch broom, leafy spurge, and garlic mustard is a major factor in the endangerment of many grassland and woodland plants.
• Predation. Exotic trespassers, including Canada's millions of domestic and feral cats, are unwelcome additions to the food chain and kill countless birds and mammals each year. Sea lampreys prey on lake trout, salmon, and walleye and have con­tributed to the collapse of entire fisheries.
• Loss of biodiversity. The decline or disappear­ance of native species resulting from alien gate-­crashers upsets the biological diversity and eco­logical balance that hold together the web of life. For example, Eurasian water-milfoil not only dis­places native plants but also makes water bodies unsuitable for fish by interfering with spawning and causing aquatic ecosystems to crash.
• Socio-economic impacts. With losses to govern­ment, communities, industry, utilities, agricul­ture, and recreation in the billions of dollars, we continue to pay a high price for the alien inva­sion. The damages caused so far by zebra mussels covering pipelines, boats, buoys, and fishing gear in Canada exceed $100 million. Millions more are spent each year on rat eradication, chemicals to kill sea lampreys, and measures to control other non-native foes. The impacts of exotic agricultur­al pests, such as gypsy moths on forestry and leafy spurge on croplands, are incalculable. Recreational opportunities, including boating and swimming, are lost when weedy intruders, like European frog-bit and fanwort, congest our water­ways. And since Canada wouldn't be the same without its native species and spaces, the alien invasion is a threat not only to our nature but also to our identity.

Canadian and international scientists recognize the enormity of the alien invasion. While they may not always agree on solutions, their expert advice has given rise to a strategy called the "restoration cycle." This ongoing process consists of: preventing the introduction and spread of exotics; controlling or eliminating them; monitoring their presence; and restoring native wildlife and habitat. You can help foil the alien invasion by employing this strategy in your own community.

• The key to prevention is awareness, so learn all about invasive foes, native friends, and how to tell them apart. Investigate the impacts of exotic intruders in your area. Then inform your school and community about this ecological menace through posters, flyers, displays, or other media. Take preventative action by obeying laws that for­bid the introduction of non-native species into Canada. If you are a boater, birder, angler, or any­one else who spends time in nature, never trans­port alien species from one site to another.
• Tackle projects to help control the invasion. Con­trol measures involve mechanical, chemical, bio­logical, and manual strategies. Manual methods, including pulling, digging, and cutting exotic plants, are the most appropriate for student.
• Monitor the presence, abundance, range, expan­sion, and impacts of non-native species over time by participating in a biological survey or launch­ing your own. The data you gather will contribute to scientific efforts to rid our lands and waters of uninvited guests.
• Take on restoration projects to recover the health of damaged habitats and bring back native animals and plants to their natural place.

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