EXOTIC SPECIES

The different species in their natural habitats are a constituting part of an interactive net that comprises many other living beings, either animal or plant, with which they share the environment. This network of interacting relationships, shaped through thousands of years of evolution, is the main sustain of the so called ecological equilibrium. When one particular specie is extracted from its original environment and inserted in a different location, the interactive network runs the risk of getting distorted, because the introduced alien being could find itself free from the a-biotic and biotic substitutes that would otherwise condition its existence, with the addition of other factors that could help to its explosive colonisation of the new area. As an example we can take the case of a plant, which in its original environment is dependant of a bird who eats its fruits and then disseminates its seeds, thus helping the plant to settle in new locations.

The causes that drive to the introduction of alien species can be the resultant of a number of factors: They can be accomplished by accident, as is the case of animals and algae that travel inside the bilges or the holds of a ship, or aboard other species during their migrations or by any other reasons. Nevertheless, the major numbers of these introductions are, by general rule, deliberate. These introductions are performed with diverse means: to embellish parks and gardens, to fight plagues, to supply the pet markets, for fishing and hunting purposes or even as innovative agricultural and stock breeding products, besides those with the goal of serving for industrial reasons.

Human activity and specially the generalisation and globalisation of commerce already existed several centuries ago, when navigation was adopted as a general way for transporting goods, which resulted in the haulage of plants and animals from one spot of the planet to another, either by will or by accident, thus bringing to us the essential cattle but also the unwelcome rats.

Plenty of time has elapsed since these classical examples occurred and many more invasions of plants and animals had taken place since.

In Argentina the list has grown very big, with more than a dozen bird species and several other dozens of mammals, although the situation regarding plants is not slighter at all, for there are actually hundreds of alien species that have already set their royals in our lands.

The Region of the Patagonia has not kept untouched by this calamity. Golden mussels (limnoperna fortunei), starling birds (sturnus vulgaris), wakame algae (undaria pinnatifida), yellow wasps (vespula spp.), Canadian beavers (castor canadensis) and red deer (cervus alaphus) among other species have gone uncontrolled, these two latter cases standing as the acutest of inconveniences to the regional environmental balance. More than fifty years ago, 25 couples of castors were taken to the island of Tierra del Fuego by means of thrusting the fur industry. The problem was that these semi-aquatic brown furred rodents found themselves in a location where they stood unrivalled within the local food chain, built dams with branches, flooded many lowlands and rotted great areas of forests. Nowadays, a number of almost 55.000 individuals are threatening to move into the main lands.

Another harmful case is that of the red deer, who feeds from the sprouts of the forests, forbidding the regeneration of the trees and which has no superior animal who predates on it (with the sole exception of men). A similar case is that of trout and salmon, imported in the early twentieth century, which not only nurture from the same sources as local fish do, but also use to devour many of them

In the same way, many of the plants which we presently do consider to be native from Argentina, are instead exotic species that were imported from Asia and the Middle East. The white willow (salix alba) was introduced by Salesian monks to Vielma and San Antonio Oeste, from where they spread to Chubut and the Limay River, thus modifying the coastal habitat and settling the grounds for new invasions. The mosquette rose (rosa aff. rubiginosa) arrived with the European immigration at the early 20th century, got adapted to the environment and settled in whichever sunny spot available, killing other native species with the aid of ruminants and birds which when feeding on it spread its seeds farther on.

Even though they are actually used for hunting and sport fishing or even as a tourist attraction, the incursion of foreign animals and plants do provoque ecological, sanitary and economical impacts. The official organisations are assertive that some urgent measures have to be taken.

It has been calculated that inside the United States a 98 per cent of the alimentary production comes from introduced species. But on the other hand, the economical losses brought by these species -ranging from mammals to microbes- would reach, according with the scientific David Pimentel of the Cornell University, some 138 thousand million dollars every year.

In the U.S.A., as well as in Argentina, a mussel has also become a matter of concern. The zebra mussel (dreissena polymorpha) has brought losses of about 2.000 million dollars by the damages they have caused to pipe inlets and plants for water desalinisation, as sustained in the last number of the Ciencia Hoy magazine.

The problem of the exotic species invasion has in a so deeply degree raised the alarm inside the United States, that in the year 2000 the by that time president Bill Clinton destined 28,8 million dollars in order of diminishing its impact and for preventing new alien species introduction.

After the great migrations performed by mankind, the world has been steadily turning into a giant supermarket of biodiversity, states the French ecological researcher Christian Leveque in the Spanish magazine Mundo Cient[ifico. The reason for this is that while human groups travel through the land, they carry not only their tamed and domestic species, but several other wild species, which are sometimes carried along unnoticed.



Avispa chaqueta amarilla - yellow jacket wasp

Homeland: Southern Europe and North Africa.
How it entered: adhered to woods or inside shipments from Europe to the United States, then travelled to Chile from where it dispersed into Argentina by its own means.
Invaded area: Western zone of the Patagonia.
Damaging effects: disturbs the open space activities due to its likings for meat and sugar. Their sting contains a very painful poison they innoculate to the fruit harvesters. It feds upon native insects.

Beaver

Homeland: Canada.
How it entered: In 1947, the Army of Argentina intentionally freed 25 couples of beavers in the Tierra del Fuego in order of promoting the hunt for hides.
Invaded area: Tierra del Fuego and the Chilean Island of Navarino.
Damaging effects: It builds dams with branches to flood the neighbouring areas and develop lagoons. The trees start to rot, leaving only naked and barren trunks. The danger of their intrusion into continental lands is very probable.

Red deer

Homeland: Eurasia
How it entered: Was brought by a landowner who sought to create hunting reserves near Santa Rosa, La Pampa.
Invaded area: Buenos Aires, Neuquén, Río Negro, La Pampa, San Luis, Tucumán and Tierra del Fuego.
Damaging effects: It disturbed the environment of the huemul, a native deer that became an endangered specie due to the seizure of its nurturing grounds.

The information used for the making of this report was obtained from
Article by David Pimentel from the Cornell University.
Ciencia Hoy Magazine
Mundo Científico Magazine, Spain