Cutting roads and railways through habitats blocks natural migration and feeding routes. Scientists have found a way to copy, or clone, the information, or genes found in cells to make new plants and animals. But no one knows if it is totally safe to take genes from one species and add them another. Well-known examples of genetic manipulation include Dolly the sheep the first cloned mammal, and adding the genes of a toad or a spider to vegetables. The educated guess stands at 12.5 million.
Exotic species are animal and plant species that find themselves outside their native habitat.
These species cause changes to the ecosystem and sometimes destroy other species native to that ecosystem. For example, zebra mussels came from Europe to the Great Lakes of North America in the ballast of ships. They spread like a plague in the waterways of the continent, attaching themselves to existing mussels and killing them. Breeding quickly, they clog up hydro-electric generators, encrust the hulls of boats and erode pipes in water treatment plants. A species is said to be extinct when it has not been seen for over 50 years.