пятница, 23 августа 2013 г.

Wolves help bears to survive and improve their diets – scientists say. Not everywhere, but in a particular place, in Yellowstone National Park.

In the early 20th century wolves were eradicated in Yellowstone. At that time it seemed a good idea and an important achievement. However, in the long run it proved to be nearly a catastrophe. In several decades this eradication of one species in the food chain caused a severe imbalance and threatened other species and even caused considerable changes in landscape over several decades. By the mid-1980s environmentalists became alarmed by the dramatic change in the Yellowstone ecosystem, and wolves had to be reintroduced in 1990s.

Unexpectedly, eradication of wolves hit hard grizzly bears. They were left almost without different kinds of berries, an essential component of their meals, especially when they prepare to hibernation. As a result, population of bears, small as it was, began to decrease.

With the wolves taken out of the ecosystem, the population of elks began to grow uncontrollably. They began to compete for food with each other and with other species. And they began to destroy some plants. For instance, by eating sprouts of trees they interfered into the natural replacement of forest.

In particular, elks began to eat berry shrubs and reduced their number considerably, leaving grizzly bears without their favorite cuisine and making them face extinction.

In about two decades after the reintroduction of wolves in the park, scientists report an increase in the number of berry shrubs and doubling of the berry seeds in droppings of grizzly bears. The decrease of their population has stopped. Wolves saved bears.

However, there is a new worry for scientists now. The ecosystem, once destabilized, cannot be stabilized easily. The number of elks since the reintroduction of wolves has fallen by a factor of six. It may happen that the next species to save will be elks.

This story shows how complicated and interrelated are ecosystems and how our unwitting interference into them can destroy them or turn them into totally different ecosystems.

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