However, the team warned that the volume of introduced species had increased markedly as the 1900s advanced.
"Introduced species are one of the principal causes of endangerment for half of endangered species, " says Daniel Simberloff, a professor of ecology and evolutionary biology at the University of Tennessee.
On April 30th Mr Alarcon issued an emergency decree to stem the tides of pollution, immigration, illegal fishing and the kind of introduced species that threaten the islands' fragile ecosystems.
Humans have introduced dozens of species into Australia - including wild horses, pigs, goats, dogs, cats, rabbits and foxes - and these have now become a major problem for the ecosystem.
Last year's count introduced a few new species to North America, including the exotic purple swamphen, an escapee now breeding in the Florida Everglades.
Left unmanaged, a natural habitat will become dominated by certain species, often invasive aliens introduced by human beings.
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Stewart Brand, the 78-year-old technologist who came to fame as editor of "The Whole Earth Catalog, " introduced an ambitious plan to recreate extinct species, using DNA from museum specimens.
Britain has a total of six deer species, four of which were introduced since Norman times.
At the same time, community plantations with fast-growing tree species for use as fuelwood are being introduced, as well as 10 000 efficient wood-burning stoves.
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The problem has long been recognized, and the aforementioned Habitats Directive -- a corollary of the 1979 Bern Convention on the Conservation of European Wildlife and Natural Habitats -- introduced a range of measures aimed at protecting endangered species (including plants, birds and fish as well as mammals).
In response to missing the biodiversity targets, Environment Minister Jane Davidson AM introduced a new national environment framework to safeguard the future of animal species and plants in Wales.
The native species is under threat from red signal crayfish, which were introduced to the UK in the 1970s and now dominate rivers.
The species was hunted to the verge of extinction before a ban was introduced in the 1960s - before then, people were rewarded for killing wolves.
Today, the species farmed in France is the acipenser baerii, or the Siberian sturgeon, introduced from Russia in 1989.
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