ALIENS

We are under attack! Our economy and our precious natural treasures are in danger! Who are the attackers? They are not foreign armies, terrorists, or extraterrestrials. But, alien species!

aSIAN LONG-HORNed BEETLE: The Asian long-horned beetle (Anoplophora glabripennis) was first introduced into the United States in 1996 and is expected to infect and damage millions of acres of hardwood trees. $30 million dollars have already been spent in attempts to eradicate this pest and protect millions of trees in the affected regions (Pimentel et al. 2005).

Who are they?
Alien species are the plants and animals that are non-native or introduced to areas outside their natural habitat. In other words, they are introduced — either intentionally or by accident — to an area or region where they did not previously occur naturally.

How do they cross the threshold?
Human introduce non-native species to a new environment as the benefits of having a favoured animal or plant available locally, or perhaps an attempt to control a native pest, overshadows everything else. International travel of people and goods has made the task easier.

    In addition, human habitation and land clearing put significant pressure on local species, and disturbed habitat is often prone to invasions.

    The alien species can even be a pre-existing one that attains dominance.

    They may be closely related with rare native species and subsequently hybridise with them. And this may lead to a decline and even extinction of the native species!

Green crab: In the mid 1990s, the introduction of the European Green Crab led to  disaster. It was found to prey preferentially on the native clams. This resulted in a decline of the native clams and an increase of the introduced Green Crab populations.	Cheatgrass: Invasive plants such as Cheat Grass and Bromus tectorum can alter the fire regime, nutrient cycling (smooth cordgrass Spartina alterniflora), and hydrology (Tama­risk) in native ecosystems! (Mack et al. 2000)

How do they intrude?
Ecosystems have their own natural balance and controls, and the native plants and animals are adapted to these conditions. Once alien species enter a new location, they establish a breeding population, and spread throughout the new area. Then they compete for limited resources or prey on the native species. The native species that are unable to adapt to the more competitive environment gradually die out.

    Unrestricted by natural controls such as predators to keep the non-native harmful species in check, the new species can wreak havoc with native species and ecosystems.

What can they cost?
Worldwide an estimated 80 per cent of endangered species could suffer losses due to competition with or predation by invasive species. Invasive plants alone cost billions to the global economy every year! The estimated damage and control cost in the US alone amount to more than US$138 billion dollars annually!

EUPHORBIA ESULA & LEAFYSPURGE: Many introduced weeds in pastures compete with native forage plants, and are toxic to cattle or non palatable due to their thorns and spines.

Economic
They can cause production loss in agriculture and forestry from seed contamination to cultivation of exotic species. And if the environmental impacts were valued in monetary terms, the costs would drastically increase. In addition, there can be loss of tourism revenues as well.

Health
The alien species often host or cause diseases that have a great impact on human health. These exotic diseases can take human as their host. Moreover, introduced birds, rodents and insects can serve as vectors of human diseases. An example of an introduced disease is the spread of the West Nile virus by mosquito vectors across North America resulting in  death of humans, birds, mammals, and reptiles! The effects are not only immediate but long-term as well.

Environmental
Their invasion can reduce biodiversity, degrade habitats, alter native genetic diversity, transmit exotic diseases to native species, and further risk endangered plants and animals! In areas with highly endemic flora and fauna such as Madagascar and Hawaii, alien species have spelled doom for many native species!

    They may be harmless and beneficial in their natural surroundings, but can destroy a different environment. They can become invasive and damage their new habitat completely!

But, human is the most dangerous invasive species that has the power to destroy and alter everything, including itself!

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