Biological invasions take place when species are deliberately or accidentally introduced and become established in environments that they have not been previously occupied.
These so-called ‘invasive species’ may set in, spread and ecologically alter the invaded community.
Biological invasions by animals, plants, pathogens or vectors are one of the greatest environmental and economic challenges and, along with habitat destruction, a leading cause of global biodiversity loss.
Invasive species are organisms that are usually transported by human beings from foreign areas. These species successively colonize native ecosystems. These have been a major threat to native species because these species show predatory behavior, cause changes in habitat and often disrupt the process of ecosystems.
One example of Bioinvasion is the introduction of Australian Brush Tail Possum which caused decline in the number of native birds in New Zealand.
There are a number of other examples also that justify the degrading impacts of invasive species in a new habitat. The spice cardamom is a problem in the lowland moist forests of Sri Lanka and Southern India.
On the other hand, the invasion of Black Pepper is causing serious threats to the biodiversity in the forest edges of Malaysia.
The Chromolaena odorata which is a shrub and which has its own values as a fallow crop in Indonesia has become the single most invasive plant in the Nature Reserves of the Tropical Regions.
The Parthenium hysterophorus, a noxious weed which competes with crop plants, causes health hazards to humans and cattle. This weed is highly allergic and reportedly causes asthma and other diseases in human beings. This exotic species was introduced from the tropical America. It was first reported in 1957 from Maharashtra.
The increasing applications of genetically engineered microorganisms and their establishments in the natural habitats are causing potential risks to the existing plants and animals.
Some traits of the genetically engineered microorganisms harm the species on which most of the natural organisms depend for their survival.
Secondly, the mixing of the genetic stock and the subsequent loss caused by this event and, the general competitive superiority of the genetically modified organisms lead to the degradation of biodiversity in a region.
Environmental biologists argue that invasive species pose one of the most important global threats to ecosystems, often spreading quickly through their new habitat so that native species become vulnerable.
It is no wonder; the increasing recognition of the invasion-related problem has resulted in a rapid growth of research into the dynamics of non-native species and their effects on native ecosystems.