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Категория реферата: Топики по английскому языку
Теги реферата: реферати, русские шпоры
Добавил(а) на сайт: Леокадия.

Animals have diversified so as to occupy many ecological niches. Herbivores form a basic link in the food chain, or food web. They are eaten by carnivores, which in turn are eaten by other carnivores. Many animals are parasites or scavengers or feed on sediments. Every animal has adaptations, such as sense organs and teeth, that enable it to find and utilize food. Some use a wide variety of foods; others specialize. Features such as camouflage and protective shells enable them to cope with predators.

Animals compete with one another for scarce resources, including food and a place to live. The interactions between predator and prey have involved a coevolution of these different parts of the ecosystem—that is, the evolution of prey is affected by the evolution of predators. Parasites, which are harmful but usually do not kill their hosts, must be able to overcome defensive adaptations. On the other hand, mutualists have cooperative arrangements with other organisms. Plants and animals can also cooperate, in the sense that food is provided by plants, and various animals effect pollination or seed distribution.

A great variety of strategies enable animals to survive and reproduce. When food in an ecosystem is abundant, the animals involved generally tend to reproduce in quantity. When intense competition for food is involved, however, the animals have to develop a more effective use of resources and tend to care for the young for a prolonged period. Where the ecosystem is stable, as in the Tropics, competition leads to complex life cycles and intricate adaptations, both structural and behavioral.

Animals often move from place to place. This enables them to locate food, avoid predators, and reproduce effectively. Through migration, birds and other animals can feed and reproduce where food is seasonally abundant. The movement of animals is limited only by the food supply, the terrain, and their individual capabilities for locomotion, and each local area and habitat has tended to evolve its own distinctive fauna.

Animals in the Human Community

Ever since true humans appeared on earth, they have lived in close association with other animals. Throughout most of that time, humans existed as hunter-gatherers who depended on wild animals for food and clothing. They also found a source of aesthetic pleasure and spiritual strength in the animal life about them. Evidence of this exists in the remarkable paintings of Paleolithic people in the caves of southern France. The religious practices of Native North Americans involved the veneration of certain animals, such as the bear, wolf, and eagle, in an attempt to acquire the power, wisdom, courage, and speed that these animals supposedly possessed.

Human societies have continued to exhibit traces of these relationships. The aesthetic appeal of animals is expressed in the mosaics and frescoes of ancient Greece, Rome, and Egypt; in the paintings of the Renaissance masters; and in countless works of more recent artists. Mystical feelings toward animals are reflected in myths and folktales, moralistic fables involving animals, and anthropomorphic animal stories for children, as well as the adoption of animal names for cars, sports teams, and so on.

Despite highly developed technology and agriculture and the domestication of many species, modern humans still depend on wild stocks of a variety of other animals, such as fish and shellfish, for food. Unmanaged commercial exploitation, however, has greatly reduced this resource and has driven some species to the edge of extinction . In addition, wild animals provide recreation in the form of sport hunting and sportfishing, bird-watching, and visits to zoos and wildlife refuges.

As humans advanced from a hunting to an agricultural existence, relationships between humans and animals changed. Animals that preyed on livestock or that destroyed crops were reduced or exterminated, and the alteration of the landscape eliminated habitats for many other species. As humans became more concentrated in cities, however, animals such as rats multiplied and became important carriers of disease.

Humans domesticated some animals for food, clothing, power, and companionship. How this came about is a matter of speculation. Through protection and selective breeding, humans changed early domesticated forms into highly productive dairy and beef cattle, sheep, swine, and poultry. Also contributing to human welfare are the dogs, cats, white rats and mice, guinea pigs, and rhesus monkeys that medical research has used to gain an understanding of human physiology and to develop drugs and procedures to combat human illnesses.

As humans continue to spread across the earth, however, they encroach on or pollute the environments of many animals, reducing remaining habitats to smaller and smaller areas. Unless this trend is reversed, much of the world's animal life faces extinction.

Скачали данный реферат: Плакилла, Tankov, Потапий, Jacenkovskij, Урсула, Mysljaev, Sebast'jan, Ядучев.
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