Endangered Species

Along with other zoo favorites, such as the orangutan, the gorilla, and various lemurs, tigers and giant pandas are threatened with extinction—the total disappearance of a living species—unless they are defended with strict protective measures.

Throughout the world, in the ever-shrinking wilderness areas, wild animals and plants are facing the ever-increasing encroachment of humans. From the vicuñas of the Andes and the whales of the open seas to the delicate orchids of Hawaii—everywhere there are animals and plants whose survival hangs in the balance. Action to save these species is of utmost importance for the future of all living things.

Extinction is nothing new. Since life first appeared on Earth billions of years ago, animals and plants have lived and died, and species have evolved and become extinct. Why and how this occurs is not always clear. Did the dinosaurs, which dominated Earth for millions of years, disappear because of massive changes in global climate? Did the last of their kind become extinct because enormous meteorites filled the sky with dust, blocking sunlight and causing plants to die? There are an endless number of possible scenarios.

What scientists do know, however, is that animals and plants either adapt or fail to adapt to changes in their environment. If they fail to adapt, or if the changes are so rapid that it is impossible to adapt, they become extinct.

Interactions Among Species

Until recently, most environmental changes took place relatively slowly, over thousands or millions of years. It was rare for one species to be directly responsible for the extinction of another. Predators might reduce the population of prey animals, but before the prey disappeared, the population of predators would be reduced because of the lack of food, thereby allowing the prey species to rebound. Such a balance can be seen in the 10-year population cycle of lynx and snowshoe hares in Canada. When the number of hares is high, lynx thrive, producing more young. In the following years, there are more lynx to eat more hares, thus reducing the hare population. Soon, because of the decrease in the number of hares, the lynx have less food available. During such times of stress, the lynx reproduce less, and fewer of their young survive. As their number declines, the population of hares increases, and the cycle begins once again.

A similar equilibrium is generally maintained between other predators and prey across the world. For this reason, scientists think that the direct effects of one species on another were probably not a major cause of extinctions in the far-distant past.