Why Alien species invasion such a matter of concern??

An alien or non-native species is an organism which humans have introduced –intentionally or accidentally -outside its previous range. It is deemed ‘invasive’ if it has negative effects on its surroundings, for example by outcompeting or predating on native species that have evolved without specific adaptations to cope with them. In such cases populations of native species can be devastated. Evidence shows that in a growing number of cases invasive alien species even cause harm to human health and society.
     At least 15 % of these alien species are known to have a negative ecological or economic impact..Invasive alien species: a  growing problem for environment and health. In many areas, ecosystems are weakened by pollution, climate change and fragmentation. Alien species invasions are a growing pressure on the natural world, which are extremely difficult to reverse......
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