Territoriality is a form of animal behavior in which an individual animal or a group defends an area against other members of the same species or against members of other species. The defended area is called a territory. An individual usually wins encounters with intruders while on its own territory, but it usually loses encounters when intruding onto another territory. A territory contains resources that the animal needs to survive and reproduce. These resources may include shelter, food, and water; places where mates can be found; and places where animals can escape from their enemies.
Definition of Territoriality is common in vertebrates (animals with a backbone), including fish, amphibians, reptiles, birds, and mammals. It is less common among insects and other invertebrates (animals without a backbone).
The size of a territory varies, depending on the effort required to defend the area and the resources available. Animals may establish small territories in the immediate vicinity of nesting sites or in areas of abundant food. They may claim large territories when resources are widely scattered. The period a territory is held may vary from less than a day to many years or a lifetime.
Animals may defend a territory by being openly aggressive, such as by chasing and fighting intruders. They also may defend the territory through signals of potential aggression. For example, a wolf marks out its territory by urinating on bushes, rocks, and other objects. The scent of urine warns intruders of the wolf's presence and the risk of an encounter. The more aggressive forms of defense generally are used when the intruder is especially persistent.
Endangered species are living things threatened with extinction-that is, the dying off of all of their kind. Thousands of species of animals and plants are endangered, and the number increases each year. Some examples of endangered species are blue whales, giant pandas, orangutans, rhinoceroses, sea turtles, snow leopards, tigers, and whooping cranes. Among endangered plants are running buffalo clover, Santa Cruz cypress, snakeroot, and many species of cactuses.
Each species of plant and animal plays a part in the delicate balance of its ecosystem, its relation to other living things and the environment. Thus, the extinction of large numbers of species threatens the survival of other living things, including human beings. As more species have become endangered, ecosystems have become unstable or collapsed. Fortunately, people have increased their efforts to protect endangered species.
Most biologists consider a species endangered if they expect it would die off completely in less than 20 years if no special efforts were made to protect it, or if the rate of decline far exceeds the rate of increase. Until the last few centuries, species became rare or died out as a result of natural causes. These causes included changes in climate, catastrophic movements in the earth's crust, and volcanic eruptions.
Today, species become endangered primarily because of human activities. Species mainly become endangered because of
loss of habitat,
wildlife trade,
overhunting, and
competition with domestic and nonnative animals.
Loss of habitat
Loss of habitat poses the greatest threat to the survival of wild species. Most animals and plants are specially adapted to live and reproduce in a specific environment or habitat and cannot survive when it is destroyed. The destruction of virgin forests by loggers and settlers and the conversion of natural grasslands into pasture for livestock have eliminated vast expanses of wildlife habitats. Marshlands have been drained for farmland and building projects. Coral reefs and many marine environments have become polluted, overfished, and even dynamited to obtain tropical fish and corals. Tropical rain forests contain the greatest variety of animal and plant life on earth, and they are being destroyed more rapidly than any other type of wild habitat.
Wildlife trade
Wildlife trade involves the capture of animals for pets, zoo specimens, and research subjects, and the killing of animals for their fur or other body parts. The capture of wild animals for commercial use has endangered many species. For example, the Spix's macaw, a parrot of Brazil, is nearly extinct in the wild because so many have been captured for private bird collectors. Many primates, including the orangutan, have become endangered by the illegal killing of the mothers to capture their babies for zoos and pet dealers. Gorillas, chimpanzees, and other primates are killed for their meat, which is sold in African markets.
Other animals have been killed in such large numbers for their fur, hides, tusks, or horns that they are nearly extinct. Rhinoceroses, wild chinchillas, the Tibetan antelope, and snow leopards are among these. Although such animals are now protected by law in the countries where they live, they are still poached (hunted illegally). Poaching also has seriously reduced the number of African elephants.
Overhunting
Overhunting has brought numerous species to the brink of extinction. The Caribbean manatee, the Asiatic lion, the dugong, and many species of pheasants have become endangered because people have hunted them for food and trophies. Many species are killed by people who believe that the animals threaten their livelihoods. Livestock owners, for example, may shoot, trap, or poison wild animals that they consider a danger to their herds. Farmers and ranchers in North America have nearly eliminated the red wolf and many species of prairie dogs, while herders in Africa have almost wiped out the Simian Wolf. Some people in the fishing industry blame seals, which eat fish, for reductions in their catch. Fishing crews have killed so many Mediterranean monk seals that fewer than 200 survive.
Competition
Competition with domestic and nonnative animals is a major threat to numerous plants and animals. On many islands, native birds, mammals, and reptiles have become endangered after people introduced domestic animals. Livestock overgraze vegetation, eliminating habitat. Domestic cats prey on birds and small mammals. Rats escape from ships and infest islands, killing small birds and their eggs. In mainland areas, stocking of game fish threatens native fish, and nonnative plants and animals crowd out many native species.
Asia, the largest of the world's continents, has a wide variety of climates. These include tropical rain forests, temperate forests, deserts, marshlands, and Arctic tundra. Such birds as broadbills, fairy-bluebirds, fruit-doves, hornbills, and leafbirds inhabit Asian forests. The male rhinoceros hornbill, like other tree-nesting hornbills, walls up his mate into a nest hole while she incubates the eggs. The golden-fronted leafbird lives in monsoon forests, which have a long dry season followed by a season of heavy rainfall. The trees in a monsoon forest usually shed their leaves during the dry season and leaf out again at the start of the rainy season. The golden-fronted leafbird feeds on fruit and insects. The blue-backed fairy-bluebird and the lesser green broadbill eat mainly fruit. Many tropical southeast Asian birds, such as the blue-winged pitta and purple-throated sunbird, have multicolored plumage.
The Himalaya, the great mountain range in southern Asia, is a biologically rich area with many species of birds. The foothills of the Himalaya provide a home to several brightly colored members of the pheasant family, including the Himalayan monal and Lady Amherst's pheasant. The Himalayan monal lives in forests above 10,000 feet (3,000 meters) high. The male has a loud ringing call. The common myna inhabits dry hillsides in India.
Some cultivated areas of Asia have become habitats for such species as the coppersmith barbet and the Java sparrow. The coppersmith barbet lives in open woodland, including orchards and gardens. It has a distinctive, monotonous "tonk" call, which it repeats over long periods. The Java sparrow was originally native to the islands of Bali and Java but has been widely introduced to other regions. It commonly resides in open areas, including rice fields, and has become a popular pet.
Birds of Africa
The Sahara, a vast desert, stretches across northern Africa and separates the continent's northern Mediterranean coastline from the land to the south. As a result, Mediterranean Africa shares many bird species with southern Europe. South of the Sahara, much of Africa has a tropical climate and a richer bird life. Rain forests provide homes for such colorful birds as the emerald cuckoo, yellow-bellied wattle-eye, and hammerkop. Many kinds of weavers live in open woodlands. The tropical grasslands have two of the world's tallest birds, the ostrich and the secretary-bird, as well as guineafowl and the crowned crane. Water birds of tropical Africa include the shoebill, the African fish-eagle, and various ducks, jacanas, kingfishers, and pelicans. Madagascar, a large island off the southeast African coast, has many unique birds, including the cuckoo roller and the helmet vanga.
They live throughout the world. Animals walk or crawl on land and dig through the soil. They swim in the water and fly through the air. They even live inside the bodies of other animals. Bats, dogs, horses, kangaroos, and moles are all animals. So are butterflies, frogs, jellyfish, pigeons, sharks, snakes, and worms.
Most kinds of animals are less than 1 inch (2.5 centimeters) long. Many are so tiny that they can be seen only with a microscope. The largest animal is the blue whale. It is about as long as five elephants in a row. Animals are not the only kind of living things. Scientists divide living things into five main kingdoms (groups)-animals, plants, fungi, protists, and prokaryotes. Fungi include molds, mushrooms, and yeasts. Protists, such as amebas, cannot be seen without a microscope. Prokaryotes, which include bacteria and certain algae, are some of the smallest, simplest forms of life.
Animals are different from other living things in many ways. For example, the bodies of animals are made up of many cells. But the bodies of prokaryotes and most protists have only one cell. Like animals, plants and fungi also are made up of many cells. However, animals can move around. Most plants and fungi are held to one place in the soil by roots or rootlike structures. For a more complete discussion of the differences between the members of the five kingdoms.
No one knows exactly how many species (kinds) of animals there are. So far, scientists have classified (grouped) and named more than 1 1/2 million kinds of animals. Over half of these are types of insects. Many new species are discovered each year. Scientists believe there may be from 2 million to as many as 50 million kinds of animals alive today. Many other kinds of animals used to live on Earth but have died out. They include dinosaurs and dodos.
Importance of animals
Animals and the web of life. Living things depend on one another. They are connected in what is sometimes called the web of life. Plants capture the energy from sunlight and use it to make roots, stems, leaves, flowers, and fruits. Animals eat the plants, or they eat other animals that feed on the plants.
When animals die, their bodies decay and release materials that help fertilize the soil for plants. Animals and plants are also connected in other ways. When animals breathe, they take in oxygen from the air and give off carbon dioxide. Green plants take in carbon dioxide and give off oxygen in a food-making process called photosynthesis. Many plants with flowers need insects or birds to carry their pollen from plant to plant. Without this transfer of pollen, these plants are not able to reproduce (create new individuals of their own kind). Some seeds are prickly and cling to the fur or feathers of animals.
When the animals move from place to place, they take the seeds with them. In this way, the seeds get dropped in new areas where they can grow into plants. The web of life relies on balance among its parts. A change in one part may mean disaster for others. For example, if all the trees in an area are cut down, then many animals that depend on them will die. For more information on how living things are linked.
Animals and people.
Animals have provided people with food and clothing since prehistoric times. Without animals, people would not have such things as meat, honey, eggs, wool, leather, or silk. At least 10,000 years ago, people began domesticating (taming) animals. Some of these animals provide food and clothing. For example, cattle supply meat, milk, and leather. Chickens lay eggs. Sheep provide wool and meat. Some domesticated animals help people work. Water buffaloes pull plows in Asian rice fields. Horses and camels carry people from one place to another. At first, people kept cats in their houses to catch rats and mice. They raised dogs to help them hunt.
Today, cats and dogs are kept largely as pets. Certain insects are useful to people. Bees make honey, which people harvest for food. Bees also pollinate many food crops, including fruits and vegetables. Silk comes from fiber made by silkworms. Some animals harm people. On rare occasions, crocodiles, lions, and tigers attack and kill people. So do grizzly bears and polar bears. Sharks sometimes kill and eat human beings. Bites from such poisonous snakes as rattlesnakes and cobras can cause death. The black widow spider has a poison that makes people extremely sick. Some animals pass diseases along from person to person. Certain mosquitoes transmit malaria and yellow fever. Some ticks carry the bacteria that cause Lyme disease and Rocky Mountain spotted fever. Some animals cause disease themselves. Worms called flukes, which live in human organs, can cause schistosomiasis. This disease infects millions of people in many African, Asian, and Latin-American countries.
People often divide animals into various groups based on certain similarities the animals share.
For example, some animals can be kept as pets, but others are wild. Arranging animals according to their similarities is a handy way of remembering and understanding them.
Some common ways of grouping animals. Animals can be grouped in many ways. They can be arranged according to whether they live on land or in water.
Animals that live on land are known as terrestrial animals. They include cats, dogs, lizards, mice, and worms. Animals that live in water are called aquatic animals. They include eels, fish, lobsters, octopuses, and whales.
Animals can be arranged by the number of legs they have. Dogs, frogs, and lizards have four legs. Bats and birds have two legs. Insects have six legs, and spiders have eight. Snakes and worms have no legs.
Another way to group animals is according to how they move. Bats, most birds, and many insects fly. Whales, fish, and squid swim. Snakes and worms crawl. Antelope and cheetahs run. Frogs, kangaroos, and rabbits hop. Some animals are cold-blooded, and others are warm-blooded.
The bodies of cold-blooded animals are warm when their surroundings are warm and cool when their surroundings are cool. Warm-blooded animals, on the other hand, almost always have the same body temperature, regardless of the warmth of their surroundings.
Birds, mammals (animals whose babies drink the mother's milk), and a few species of fish and insects are warm-blooded. All other kinds of animals are cold-blooded. Animals are also commonly divided into groups according to whether they have backbones. Invertebrates do not have backbones, but vertebrates do.
The vast majority of animals are invertebrates. They include clams, insects, jellyfish, sea urchins, snails, spiders, sponges, and worms. Birds, fish, mammals, and reptiles are vertebrates. So are amphibians-frogs, salamanders, and other animals that spend part of their lives in water and part on land. The scientific classification of animals involves grouping animals according to the biological relationships among them. This orderly arrangement of animals depends in part on the features the animals share.
In general, the more features they share, the more closely they are related. However, the scientific classification of animals is based mainly on the belief that certain animals share a common ancestor. Animals with a more recent common ancestor are more closely related than those who share an ancestor further back in time. In a somewhat similar way, brothers and sisters are more closely related than are cousins. Brothers and sisters share parents.
First cousins share grandparents. In classifying animals, zoologists (scientists who study animals) divide them into ever-smaller groups that have more and more features in common. The largest group is the kingdom Animalia itself, which includes all animals. Next, each animal is placed in a group called a phylum. Each phylum is divided into groups called classes. The classes are broken down into orders, and the orders into families.
The families are split into genera, and the genera into species. The singular form of genera is genus, but the word species may be either singular or plural. Among the animals that scientists have classified are about 13,000 species of flatworms; 50,000 species of clams, oysters, and other mollusks (soft-bodied animals, most of which have a hard shell); 1,000,000 species of insects; 30,000 species of spiders; 21,000 species of fish; 4,000 species of amphibians; 6,500 species of reptiles; 9,700 species of birds; and 4,500 species of mammals.
Each species belongs to one phylum, one class, one order, one family, and one genus. For example, tigers belong to the kingdom Animalia, the phylum Chordata, the class Mammalia, the order Carnivora, the family Felidae, and the genus Panthera. They are members of the species Panthera tigris. Lions are related to tigers. They belong to the same kingdom (Animalia), phylum (Chordata), class (Mammalia), order (Carnivora), family (Felidae), and genus (Panthera) as tigers. But lions are classified in a different species-Panthera leo, also written simply as P. leo. Next >>>
