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10 Dec 2018

Read the information on exotix and invasive species and answer this question;

writing assignment : Maximum 1 page answer is needed for the below question

Question:Should the government work to prevent the introduction of exotix species to Canada??

From Freeman et al. 2019. Biological Sciences.

Global trade and global travel have vastly increased the rate of exchange of plants, animals, fungi, and microorganisms around the world. A nonnative species that is introduced into a new area is called an exotic species. Exotic species do not necessarily pose problems, and they can even be beneficial in some circumstances. But some exotic species pose a direct threat to native species by eating them, competing with them, causing disease, or other types of interactions. For example, a lethal fungus is spreading from Asia in the exotic salamander pet trade, endangering native salamanders worldwide. Exotic species can also pose indirect threats by changing the local biotic or abiotic resources.

If an exotic species is introduced to a new area, grows to large population size, and disrupts species native to the area, it is called an invasive species. For example, Burmese pythons were set free by pet owners into the Florida Everglades and are now dramatically affecting native wildlife there. Argentine ants have dispersed around the world in food shipments and are forming supercolonies that outcompete native ants. The round goby, a small benthic fish from Eastern Europe first detected in Ontario rivers in 1990, has since spread to all five Great Lakes. The round goby competes for food and spawning habitat with native fishes and is thought to be responsible for the local extinction of native sculpin species from areas of Lake Michigan.

The impact of invasive species can also be beneficial. McMaster University biologist James Quinn and his colleagues investigated the diet of double-crested cormorant chicks in Lake Ontario to determine whether the parent birds were taking advantage of the newly abundant round goby to feed their young. They found that the round goby was the second most frequent fish species eaten by cormorant chicks, suggesting that piscivorous birds are changing their diet to feed on this invasive fish.

Genetic analysis carried out by Tony Einfeldt, a researcher at the University of New Brunswick, suggests that Hediste diversicolor, an abundant polychaete worm in the Bay of Fundy, is an invasive species that originated in France. H. diversicolor is an important prey item for birds and fish in the mud flats in the Bay of Fundy. The polychaete is a poor swimmer with low dispersal ability and could not have made its own way to Canadian waters. The polychaetes live in mud, so they would not end up in ballast water taken in by ships to balance the mass of their cargo. Einfeldt suggests that these species were likely carried to Canada in the early 1600s by ships used by early European explorers such as Samuel de Champlain and Henry Hudson. Prior to 1880, ships lacked ballast tanks, and sailors loaded ships with intertidal material, including rocks, sticks, and mud, as ‘dry ballast’. Hediste diversicolor likely arrived in the Bay of Fundy in this intertidal mud. The worms form burrows and bring water currents through their burrows as they feed. As a result, H. diversicolor acts as an ecosystem engineer, altering nutrient flow and restructuring the muddy intertidal where it lives. The invasive polychaete is also a major food source for millions of birds and fish in the Bay of Fundy and plays a key role in the ecology of the area. “The reason that many of these birds and fish come to our mud flats is to feed on these prey. There are so many of them,” says Einfeldt. “The idea that so much of what our ecosystem runs on came from our history — it's very exciting.”

Modified from Breining. 2009. A New View on Exotic Species. Yale Environment 360

When biologist Mark Davis talks about invasive species, he eventually comes to LTL, his shorthand for Learn to Love them. Invasive species are here to stay, says Davis, so get used to them, and forget about ripping out the fast-spreading plant purple loosestrife on a large scale or throwing Asian carp on the bank to die. If newcomers are only changing the ecosystem but “not causing significant harm,” then “altering one’s perspective is certainly much less costly than any other sort of management program.”

Davis claims that assuming that invasive species are inherently bad, that ecosystem integrity can be measured by the number of alien species, or even that newly arrived species are functionally different from longtime residents, simply isn’t supported by science. Many introduced species have proven valuable and useful, including crops (from apples to wheat), horticultural plants (hostas and Norway maples), and game species (ring-necked pheasants and brown trout). He holds firm to that position, while conceding that some newcomers can be terribly destructive.

“Some invasive species are causing problems,” admits Davis, who says he supports control programs where damage is great and controls stand a chance of success. One highly destructive invasive species causing great economic harm, for which Davis supports eradication programs, is the emerald ash borer, a beetle—recently introduced into eastern Canada from Asia—that typically kills 99% of ash trees in affected areas.

Today, biologists continue to wage a war on alien species that have taken root by accident or design. Zebra mussels, Dutch elm disease, purple loosestrife, Eurasian water milfoil, American bullfrogs, gypsy moths—Canada is beset by exotic species invading native forests, spreading across prairies, and clogging streams and lakes. Davis takes issue with some conventional views of exotic species.

Because native species evolved in a specific ecosystem and exotics didn’t, natives are better suited to their environment. In fact, says Davis, a scientist who didn’t know the history of individual organisms would have difficulty in distinguishing natives from non-natives. The Galapagos Islands—a world heritage site of biodiversity—provide just such an example. For years, conservationists fretted over invasive weeds overrunning the islands. Because the weeds were out of control, conservationists assumed they were non-natives, recently introduced by humans. Research showed, however, that the plants were native and had been present since prehistoric times.

Diverse communities of native species resist invasions by alien species. While carefully controlled experiments on small plots have confirmed this idea, studies in natural forests and grasslands show the opposite, says Davis. Natural disturbances, such as disease or fire, and fluctuations in resources in diverse communities offer plenty of footholds for invaders.

Pristine ecosystems are highly evolved and well-ordered. Again, ecologists have little evidence for this, Davis says. Ragtag assemblages of exotics and natives quickly adapt and perform about as well. “If you view [nature] as a continually changing tumult, the introduction of new species isn’t necessarily looked at as a huge threat.” He cites the example of regeneration of forests in Puerto Rico, where non-native species are facilitating the re-establishment of native species.

The spread of invasive species threatens to drive natives extinct. Rarely happens, Davis says, except on islands, in lakes, or in other insular environments. Usually it’s the opposite—the appearance of exotics increases species richness, he maintains. Throughout Canada, local ecosystems have roughly 20 percent more plant species than they once did because of the addition for foreign species.

Exotics signify a “degraded” ecosystem. “There isn’t such a thing as a healthy ecosystem or a sick ecosystem,” Davis says. “Ecosystems have no goal or purpose. They’re just the species and the physical and chemical processes taking place.”

In some cases, invasions of invasive species do threaten native species with extinction. Chestnut blight, caused by an introduced fungus, swept across southern Ontario in the 1950s and virtually exterminated the native chestnut tree. Ecologist Dan Simberloff says, “We know it caused total global extinction of at least seven species of moths that were host-specific only on North American chestnuts.”

Even if exotics don’t drive native species to extinction, they can completely transform ecosystems. “There are some biotic communities that have entirely disappeared because of invasive species,” says Simberloff. “There are others that have drastically changed over large areas.” For example, Eurasian cheat grass now dominates millions of hectares of Western range, displacing native bunch grasses and reducing the value of the range for livestock.

James Carlton, Pew Fellow in Marine Conservation, contends that biologists can distinguish natives from exotics. “We can easily distinguish natives from many (not all!) non-natives many times in many ways, based very much on how they function in an ecosystem. Native species are often finely tuned physiologically to the environment, whereas nonnative species may possess a repertoire of adaptations that clearly do not match the environment.”

Conservation biologist Dov Sax became positive about the impact of invasive species as an undergraduate at the University of California, Berkeley. A professor leading a field trip described the Bay Area’s abandoned plantations of Australian eucalyptus trees as a ‘biological desert.’ Says Sax, “There was all kinds of stuff growing in there. I found there were really a similar number of species in both [native oak and eucalyptus] woodland types. Exotics weren’t always doing the awful things people thought they were doing.” Land managers can’t begin to control the thousands of exotics that reach native ecosystems through globalized trade and travel. “Conservation biology in the past has been built around the idea of preventing change,” says Sax, “but it’s impossible to do.”

In a matter of decades, researchers believe, animals and plants are adapting to life in a warmer world. Some species will be unable to change quickly enough and will go extinct, but others will evolve, as natural selection enables them to carry on in an altered environment. With global warming pushing some animals and plants to the brink of extinction, conservation biologists are now saying that the only way to save some species may be to move them. The future landscape will be home to “novel ecosystems,” never-before-seen agglomerations of species, of which exotics will be a key — and often valued component, Sax and others say. “If we lump them into this category of all being evil or awful in some way,” he says, “we may blind ourselves to those situations where they’re actually providing a benefit either for humans or for biological conservation.” For example, a recent study of two nonnative wetland plants, suggests they provide waterfowl habitat, biomass production, and nitrogen retention that equals that of native species. Davis feels we should focus instead on disease organisms, agricultural pests, and other threats and says, “It’s important to distinguish harm from change.”

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Trinidad Tremblay
Trinidad TremblayLv2
13 Dec 2018

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