General zoology.

The environments of life. We do not know whether life occurs elsewhere in the universe. On the earth it exists under certain physical conditions. These include the presence of (1) certain chemical elements that go to make up the protoplasm of living organisms; (2) energy from the sun as solar radiation for plants to synthesize organic compounds usable as animal food; (3) an atmosphere containing oxygen; (4) water; (5) certain temperature limits. Exceptions occur with respect to animals that do not require direct sunlight and a few that gain their oxygen indirectly. Life usually occurs within temperature limits of about 3^o and 45^o .Many animals can exist only within a much narrower range, and a few survive greater or less temperatures.

Water covers about 72 percent of the earth’s surface. The fresh waters of lakes and streams contain sparse amounts of dissolved chemicals. Other inland brackish or alkaline water have a large mineral content. The salt waters of the oceans and their connecting bays and inlets average about 3.5 per cent in dissolved minerals, sodium chloride (NaCl), being the major component.

The end result of the differences in topography, water relations, and climate is to produce a wide variety of physical environments over the earth; these are the habitats or places where plants and animals grow and live.

Distribution. Animals inhabit practically all parts of the earth from great depths in the sea to the highest mountains and from the poles to the equator. Each species of animal has a definite range or area of distribution, determined by its needs as to food, shelter and reproduction. Various kinds of animals live in all sorts of water, fresh or foul, alkaline or salt. Others are found in land environments from the hottest and driest desert to the most humid of tropical forests and in all sorts of plant growths.

The majority of animals are free-living, able to move about independently, but water dwellers are fixed in placed, or sessile. Still others are parasites that live on or within other animals at the expense of the latter.

Interrelations. No animal lives entirely to itself. Each is affected in varying degree by the features of its physical environment and by the other animals and plants that constitute its biological environment. The distribution of many land animals is determined by the kinds of plants or plant growth upon which they rely for food or cover. Most animals are affected by enemies, diseases or competitors. The total of all these interactions comprises the “web of life” or the “balance of nature”, a dynamic complex of forces, physical and biological that affects every living organism, including man.

Relations of animals to man. Animals bear many relations to human affairs, some being very useful and others harmful. The domestic mammals and birds, together with fishes, are the principal sources of human protein food and of various oils and fats. Oysters, crabs, lobsters, shrimps and other aquatic animals also serve as food. The wool of sheep and the pelts of various fur-bearing mammals provide clothing, and bird feathers are used in pillows and quilts. The hides of animals provide leather and glue, the hair is made into felt, and from glands and other internal organs many medicinal preparations are made. Honey, beeswax, tortoise shell and natural sponges are other useful animal products. The livestock and meat-packing industries, the commercial fisheries, the fur trade and beekeeping provide profitable employment for thousands of persons.

Among the harmful animals the larger predatory animals are no longer dangerous to men in civilized countries, but they kill domestic livestock and useful wild animals. The insects and rodents that feed upon crop plants, grasses, herbs or trees take a toll from farmers that amounts to many millions of dollars annually and necessitates large expenditures for control. Other insects and the “house” rats and mice damage stored foods and other property. Many kinds of parasites – protozoans, worms, insects and ticks - bring illness and death to man, his domestic livestock, and useful wild species. The parasites of malaria and yellow fever carried by mosquitoes, the bacteria of plague transmitted by fleas, the typhus spread by lice, and other diseases carried by animals have exercised a dominant role in the history of mankind down through the ages. Some insects, spiders, scorpions and snakes are dangerously poisonous.

Wordlist:

alkaline – щелочной

foul - загрязненный

sessile -сидячий; неподвижный, фиксированный

protozoan - простейшее животное

take a toll - приносить потери

meat-packing industry - мясоконсервная промышленность