What would happen if all the lions in Africa are carried away to some other place? The deer population will rise as there will not be anyone to kill them. With this population boom, the deer would need more food.
After a point, there will no grass left to feed subsequent generations. This would lead to the destruction of the entire ecosystem which thrives and sustains itself on the grass. And the grasslands will turn into a desert.
Similarly, if an organism were to reach a place where it finds suitable living conditions but no natural enemies, it would spoil that ecosystem as well. This is exactly what is happening.
Ships carry huge loads of cargo which they transport from port to port. When these ships are not carrying cargo, they need something equal to the weight of cargo to move steadily on water. This is done by filling huge tanks called ballast tanks with water.
When the ship has to take on the cargo, the ballast tanks are emptied. When these tanks are filled, huge number of marine organisms like bacteria, microbes, fishes, cysts, larvae and crabs get into the tanks.
And when the water is pumped out in foreign waters, these organisms land in a new habitat where they flourish. But these new waters seldom have the traditional predators they face in their native areas.
In USA, the European zebra mussle, a fresh water mollusc, has infested over 40 percent of internal waterways. In southern Australia, the Asian kelp, an algae, is invading new areas and have displaced native sea bed algae, reports the Down to Earth magazine.
These organisms who go without any checks turn into militants, killing and encroaching upon the territory of native animals. This process is called bio-invasion.
Efforts are now being made to curb such widespread mixing of population causing death and damage to local environments.