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  • Massive vines that blanket the southern United States,

  • climbing as high as 100 feet as they uproot trees and swallow buildings.

  • A ravenous snake that is capable of devouring an alligator.

  • Rabbit populations that eat themselves into starvation.

  • These aren't horror movie concepts.

  • They're real stories,

  • but how could such situations exist in nature?

  • All three are examples of invasive species,

  • organisms harmful not because of what they are,

  • but where they happen to be.

  • The kudzu vine, for example,

  • had grown quality in its native east Asia, eaten by various insects

  • and dying off during the cold winters.

  • But its fortunes changed

  • when it was imported into the southeastern United States

  • for porch decoration and cattle feed.

  • Its planting was even subsidized by the government to fight soil erosion.

  • With sunny fields, a mild climate, and no natural predators in its new home,

  • the vine grew uncontrollably

  • until it became known as the plant that ate the South.

  • Meanwhile in Florida's Everglades, Burmese pythons,

  • thought to have been released by pet owners,

  • are the cause of decreasing populations of organisms.

  • They're successfully outcompeting top predators,

  • such as the alligator and panther,

  • causing a significant reduction in their food sources.

  • They're not a problem in their native Asia

  • because diseases, parasites, and predators help to control their population size.

  • And in Australia, European rabbits eat so many plants

  • that they wipe out the food supply for themselves and other herbivores.

  • They're a pretty recent addition,

  • intentionally introduced to the continent because one man enjoyed hunting them.

  • Like the Burmese pythons,

  • various factors in their native habitat keep their numbers in control.

  • But in Australia, the lack of predators

  • and a climate perfect for year-long reproduction

  • allows their populations to skyrocket.

  • So why does this keep happening?

  • Most of the world's ecosystems

  • are the result of millennia of coevolution by organisms,

  • adapting to their environment and each other

  • until a stable balance is reached.

  • Healthy ecosystems maintain this balance via limiting factors,

  • environmental conditions that restrict the size or range of a species.

  • These include things like natural geography and climate,

  • food availability,

  • and the presence or absence of predators.

  • For example, plant growth depends on levels of sunlight and soil nutrients.

  • The amount of edible plants affects the population of herbivores,

  • which in turn impacts the carnivores that feed on them.

  • And a healthy predator population keeps the herbivores from becoming too numerous

  • and devouring all the plants.

  • But even minor changes in one factor can upset this balance,

  • and the sudden introduction of non-native organisms

  • can be a pretty major change.

  • A species that is evolved in a separate habitat

  • will be susceptible to different limiting factors,

  • different predators,

  • different energy sources,

  • and different climates.

  • If the new habitat's limiting factors fail to restrict the species growth,

  • it will continue to multiply,

  • out-competing native organisms for resources

  • and disrupting the entire ecosystem.

  • Species are sometimes introduced into new habitats through natural factors,

  • like storms,

  • ocean currents,

  • or climate shifts.

  • The majority of invasive species, though, are introduced by humans.

  • Often this happens unintentionally,

  • as when the zebra mussel was accidentally brought to Lake Erie by cargo ships.

  • But as people migrate around the world,

  • we have also deliberately brought our plants and animals along,

  • rarely considering the consequences.

  • But now that we're learning more

  • about the effects of invasive species on ecosystems,

  • many governments closely monitor the transport of plants and animals,

  • and ban the imports of certain organisms.

  • But could the species with the most drastic environmental impact

  • be a group of primates who emerged from Africa to cover most of the world?

  • Are we an invasive species?

Massive vines that blanket the southern United States,

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B2 TED-Ed invasive native climate limiting habitat

【TED-Ed】The threat of invasive species - Jennifer Klos

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    VoiceTube posted on 2016/10/03
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