This happens because none of the native species will recognize the exotic as a threat or even a source of food.
Overexploitation can cause the extinction of a species; this is due to the rate at which the animals are taken. Many species have been hunted for sport or for profit until only a small number remains. Unrestricted whaling during the 20th century is an example of this and the whaling industry brought many species of whales to extremely low population sizes. When several whale species were nearly extinct a number of nations finally agreed to abide by an international moratorium on whaling. Due to this moratorium, some whale species, such as the Grey whale, have made a remarkable comeback, while others still remain endangered (Reichhardt p. 322).
Disease, pollution, and limited distribution are more factors that threaten various plant and animal species. If a species does not have the natural genetic protection against particular pathogens, an introduced disease can have severe effects on that specie. For example, rabies and canine distemper viruses are presently destroying carnivore populations in East Africa (Campbell). Domestic animals often transmit the diseases that affect wild populations; demonstrating again how human activities lie at the root of most causes of endangerment. Pollution has seriously affected multiple terrestrial and aquatic species, and limited distributions are frequently a consequence of other threats; populations confined to few small areas due to of habitat loss, for example, may be disastrously affected by random factors.
The benefits of saving endangered species are great in numbers. Many plants and animals hold medicinal, agricultural, commercial and recreational values. They must all be protected and saved so that future generations can experience their presence and value. .
Plants and animals are responsibly for a variety of useful medications.
