Within the scenario of the changes being suffered by the environment, the impoverishment of biodiversity is perhaps the most significant because it is the only change that is completely irreversible. Any animal or plant species, regardless of how insignificant it may seem, plays an irreplaceable role in the ecosystem of which its forms part and is the product of thousands of years of evolution.
When the last representative of a particular type of plant or animal disappears, it will never exist again. Sadly, this is the case with many species. The UICN, a major international organization for nature conservation, estimates that world-wide one or two plant species become extinct each day whilst the figure for animals varies from 50 to 250 each day.
There are three main causes for the extinction of living beings. The best known cause, hunting, is considered as being responsible for the disappearance of almost a quarter of species. The destruction of habitats accounts for 36% of the loss.
The least known cause, yet one which is of major importance, is the introduction of species that are responsible for 39% of the destruction. Literature contains numerous examples of plants and animals that have been taken by man from one region to another, causing real ecological disasters. A recently published case shows how the sapo cururu, a creature familiar to Brazilian children, could cause environmental damage in Australia, where it was introduced in the middle of the century.