Characteristics of Rainforests

Characteristics of rain forests, The temperature in a tropical rain forest varies little. It rarely rises above 95 °F (35 °C) or drops below 64 °F (18 °C). In many regions, the average temperature in the hottest month is only 2 to 5 Fahrenheit degrees (1 to 3 Celsius degrees) higher than the average temperature in the coldest month. Most rain forests receive more than 80 inches (203 centimeters) of rain annually. Some areas may receive more than 250 inches (635 centimeters) of rain each year. Thundershowers can occur more than 200 days a year.

Rain forest soils vary greatly from place to place. In many areas, the soil is acidic and infertile because years of heavy rains have washed out most of the nutrients (nourishing substances). Most rain forest nutrients are part of living plants. Small amounts of nutrients occur in a thin layer of topsoil that contains decaying vegetation.

Rain forest trees have developed several ways of capturing nutrients. For example, they obtain nourishment from rainwater that collects in their leaves or along their trunks and branches. They also withdraw nutrients from their old leaves before they shed them. The roots of most rain forest trees grow close to the surface and quickly absorb soil nutrients before they wash away. Special fungi called mycorrhizae grow in or on many of the roots and help them absorb minerals from the soil.

Rain forests grow in four major layers: (1) the canopy, or top layer; (2) the sub-canopy, a layer of trees just below the canopy; (3) the understory, a shady lower area; and (4) the floor. The tallest trees, known as emergents, grow more than 165 feet (50 meters) tall. The crowns (tops) of these trees dominate the canopy. Emergents receive the greatest amount of sunlight, but they must endure high temperatures and strong winds. The crowns of other trees in the canopy usually form a nearly continuous covering of leaves 65 to 165 feet (20 to 50 meters) above the ground. Some tall trees have large growths called buttresses that extend from the base of the trunk and help support the tree.

More than 70 percent of rain forest animal and plant species reside in the canopy and sub-canopy. Many tree branches have a dense covering of epiphytes, plants that grow on other plants and obtain nourishment from the air and rain. Vines called lianas often climb on or around the trunks and branches of trees.

The shady understory shelters small palms, young trees, and herbaceous (nonwoody) plants that can grow in dim light. Many popular house plants, such as philodendrons, dieffenbachia, and ferns, are developed from species that live in this area. Some scientists believe only 1 percent of the sunlight available to emergent trees reaches the understory.

A thin layer of fallen leaves, seeds, fruits, and branches covers the forest floor. This layer quickly decomposes and is constantly replaced.

The layers of a rain forest continually change. Large old trees die and fall to the ground, leaving a gap in the canopy. Direct sunlight penetrates through to the understory and stimulates the growth of seedlings, saplings, and small trees below. The small trees slowly stretch upward into the canopy. As they branch and expand their crowns, they fill the gaps in the canopy. A mature rain forest consists of a mixture of closed canopies, gaps, and patches of growing trees where the canopy is being rebuilt. The regeneration of many rain forest trees depends on gaps developing regularly in the canopy.

Plants and animals. About 45 percent of the world's plant species occur in tropical rain forests. Scientists have counted over 250 species of trees in small areas of Asian and South American rain forests. A similar plot of land in a northern temperate forest would have only about 10 to 15 tree species. In addition to trees, rain forests support a great variety of bamboos, herbs, and shrubs. Climbing vines, ferns, mosses, and orchids grow directly on the trunks and branches of large trees.

Because of continual moisture and warmth, tropical rain forests stay green all year. Most rain forest trees continually lose old leaves and grow new ones. Only a few species lose all of their leaves for a brief period.

Fish, amphibians, reptiles, birds, and mammals abound in the rain forest and its rivers. However, insects rank as the most plentiful rain forest animals. An individual tree in a South American rain forest may support more than 40 species of ants. Scientists have counted about 1,200 species of beetles living in only 19 tree crowns from Panama.

Plants and animals in the rain forest depend on one another for survival. Many animal groups, especially insects and birds, pollinate the flowers of rain forest trees. Such animals receive food from the flowers' nectar. In return, they pollinate the next flowers they visit. Some trees rely on only one species of insect for pollination. Many rain forest trees also depend on animals to disperse their seeds. In the Amazon rain forest, fish disperse the seeds of some trees.

DEFINITION OF DOMINANCE

Definition of Dominance is a form of behavior among individual animals that shows their ability to win aggressive encounters with other animals. These animals may be members of the same species or of different species. Dominance determines which individuals have first choice of resources that are needed to survive and reproduce and that are in limited supply. These resources include food, water, a resting place, or mates. Animals that lose the aggressive encounters or give in to dominant individuals without a fight are called subordinates. Subordinates that are denied use of scarce resources may be among the first to die or to leave an area.

In a group, a particular individual may be dominant to some members and subordinate to others. This results in a dominance hierarchy--that is, a ranking of individuals by their dominance in relation to each other. In many cases, an individual is subordinate to all those ranked above it and dominant to those below it. This type of ranking is called linear dominance hierarchy. However, dominance hierarchies may be more complicated. For example, in circular dominance hierarchy, individual A may be dominant to individual B and B dominant to individual C, but C is dominant to A. Individuals can improve their position in the group's dominance hierarchy as they gain experience or maturity, or as their reproductive condition changes.

Encounters that establish dominance only occasionally include actual fighting. In most cases, these encounters involve only signals that indicate an individual's willingness or ability to win a potential fight. An individual's large size or threatening natural weapons, such as the horns of mountain sheep or the powerful jaws of a wolf, might cause subordinates to give up without a fight.

Dominance differs from territoriality, a form of animal behavior in which an individual or group claims a certain area as its own. A dominant individual usually can win wherever it is.

DEFINITION OF ADAPTATION

Definition of Adaptation is a characteristic of an organism that makes it better able to survive and reproduce in its environment. No two organisms of the same species are exactly alike. Every trait, such as size, color, and personality, shows some variation. Additionally, in nature, organisms produce more offspring than can survive. The offspring most likely to survive and reproduce are those with adaptations best suited to the environment. Offspring with variations less suited to the environment do not compete as successfully for food, water, and other necessities. This process of competition, by which those best adapted are most likely to survive and reproduce is called natural selection.

Some forms of life are adapted to living in many different environments. For example, people live in all kinds of climates, ranging from the tropics to the Arctic. Thus, human beings are generalized-that is, the human body has adaptations that enable people to live in widely different environments. But such organisms as mosquitoes and bamboo plants are more specialized. Because of their physical makeup, they can live only in a rather warm, wet climate.

Living things often die when they cannot adapt to a changing environment. Many kinds of plants and animals that once lived on the earth have become extinct. For example, millions of years ago, dinosaurs roamed the earth. But the environment in which they lived changed. The dinosaurs failed to adapt, and they died out.

The word adaptation also refers to the ability of living things to adjust to varying conditions in their environment. If people move to the mountains, their bodies adapt to the lower oxygen supply at high altitudes by making more oxygen-carrying red blood cells. A dog adapts to warm weather by shedding its hair. Adaptations that occur over a relatively short time, particularly because of changes in climate, are often called acclimatizations.

ENDANGERED SPECIES

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

1. loss of habitat,
2. wildlife trade,
3. overhunting, and
4. 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.

Birds of Asia and Africa

Birds of Asia

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.

Where Animals Live

Animals live in many kinds of places. The place where an animal lives is called its habitat. Each type of habitat presents a special challenge to animals. For example, animals that live in polar regions must withstand bitter cold. Those that inhabit the tropics face extreme heat. In spite of these challenges, animals can be found everywhere on Earth. They live on the highest mountains and in the deepest oceans. They roam the driest deserts and the wettest rain forests. They swim in fresh water and salt water.

Each habitat supports many kinds of animals. In most cases, the animals are the same kinds that have lived in those surroundings for thousands of years. As a result, the animals have developed bodies and ways of life that suit them to that particular habitat. No single species of animal can survive everywhere. For example, tropical fish from the Amazon River thrive in warm water but cannot withstand the cold streams of the Andes Mountains. On the other hand, many kinds of fish that live in the Arctic Ocean would die if they were exposed to the warm waters of the Caribbean Sea. However, some animals may travel between habitats from time to time. For example, African elephants eat both grass and tree parts and so move between grassland and forest. But these animals would not be able to withstand the freezing temperatures of the polar regions.

Some habitats, including many forests and grasslands, are being destroyed by human beings. The destruction of these habitats usually causes the death of many animals. When people convert grassland to farmland, for example, they destroy the homes and source of food of many species. Without these necessities, some animals will die immediately. Others may try moving to another grassland. But the new area may not have enough food and shelter to support the additional wildlife. As a result, many more animals will die.

Some of the major animals, grouped according to seven types of habitats: (1) mountains, (2) grasslands, (3) temperate forests, (4) tropical forests, (5) deserts, (6) polar regions, and (7) oceans.

Animals of the mountains

Mountains support a variety of animal life. The numbers and kinds of animals found on mountains vary with altitude. More animals and more kinds of animals live at lower altitudes than at higher ones, largely because of the differences in climate between elevations. Generally, mountain climates become colder, wetter, and windier with increasing altitude. The air also gets thinner and has less oxygen. In addition, fewer plants are found at higher elevations, and therefore less food is available for animals.

Bears, deer, elk, and mink make their homes on the forested lower slopes and in the wooded or grassy valleys of mountains. Rainbow trout and graylings swim in mountain streams. Many mountains have meadows of grasses and herbs. These meadows are home to chinchillas, ibexes, llamas, vicunas, and yaks. Butterflies, grasshoppers, and spiders also live there.

Above the timber line-that is, the line beyond which trees will not grow because of the cold-stand rocky cliffs and peaks dotted with shrubs, mosses, and other plants. Small meadows are also found there. Sure-footed bighorn sheep and mountain goats dwell among the windswept rocks, as do furry marmots and pikas. High on the snow-capped peaks, only a few insects, spiders, and ice worms can survive. Golden eagles and some other birds fly above the mountains. A large African vulture, Ruppell's griffon, has been known to soar as high as 36,600 feet (11,150 meters).


Animals of the grasslands

Grasslands include the prairies of North America, the pampas of South America, the plains of Europe, and the steppes of Asia. The savannas of east Africa have more grassland animals than any other area.

Rainfall in grasslands is seasonal, and animals sometimes travel great distances to find green grass. Gazelles, gnus, and zebras migrate by the thousands through the African savannas. Smaller groups of elephants and rhinoceroses also feed on the grasses there. Such meat-eating mammals as cheetahs, hyenas, and lions roam the savannas in search of prey. The savannas are also home to giraffes, jackals, ostriches, secretary birds, and termites. In addition, hippopotamuses live in and near bodies of water in African grasslands. Animals of other grasslands include the kangaroos and wombats of Australia, the cavies and rheas of South America, and the coyotes and prairie dogs of North America.

Many animals of the grasslands have become endangered due to loss of their habitat and to overhunting. The rich soils of grasslands are ideal for farming, and people have converted many such areas to farmland. Many of the large grassland animals are favorite big game for hunters. For example, the once-plentiful pampas deer of South America have become extremely rare. As the pampas are converted to farmland, the tall grass that grows there disappears. Without this grass, the pampas deer have no shelter and become easy prey. Bison once grazed in huge herds in the Great Plains of North America. But so many of these animals were killed by hunters or died as their grassland habitat was converted to farmland that they were nearly wiped out.

Animals of the temperate forests

Temperate forests consist largely of deciduous trees and evergreen trees. Deciduous trees shed their leaves in the fall and grow new ones in the spring. Evergreen trees have leaves that live two or more years. Some evergreens have needle-shaped leaves. Most temperate forests are in Asia, Europe, and North America. Australia also has some temperate forests. 

Many forest animals have small bodies that allow them to move easily through the underbrush. Forest mammals include chipmunks, mice, opossums, porcupines, raccoons, skunks, and squirrels. Bears, deer, and wild boars also live in temperate forests. Bobcats and wolves were once common in woodland areas. However, so many of these predators have been hunted and trapped through the years that they have become rare.

Salamanders are often plentiful in temperate forests. They hide in the leaf litter or under rocks, where they feed on insects and other small organisms. In wet forests, slugs and other snails are common. Beavers, fish, frogs, muskrats, otters, salamanders, and turtles live in or near woodland streams, ponds, and lakes. Great numbers of birds nest in the trees and shrubs.

Many temperate forests have been cleared for farms and cities, and many others have been cut down for fuel and lumber. This deforestation (destruction of forests) places woodland animals in danger. Extensive logging in the Pacific Northwest of the United States, for example, has destroyed much of the habitat of the spotted owl, threatening the existence of that species.


Animals of the tropical forests

Tropical forests stay warm all year and receive plentiful rainfall. These forests are found in Africa, Asia, Australia, Central and South America, and the Pacific Islands. More kinds of animals live in tropical forests than in any other habitat. Scientists estimate that perhaps as many as 30 million species of tropical animals have not even been discovered yet.

Insects make up the largest single group of animals that live in tropical forests. They include brightly colored butterflies, huge colonies of ants, mosquitoes, and camouflaged stick insects. Spiders are also plentiful.

Many tropical birds, such as quetzals and parrots, are spectacularly colored. The broad leaves of trees in tropical forests form a thick overhead covering called a canopy that blocks nearly all sunlight from reaching the forest floor. 

Many kinds of animals live in the canopies of tropical forests. They include harpy eagles and toucans; tree frogs; flying dragons; spider monkeys and howlers; gibbons and orangutans; sloths; slow lorises; tree boa constrictors; bats; and wasps, beetles, and leaf-cutting ants.

Animal live throughout the world

Animals come in many shapes and sizes.

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.

Kinds of Animals

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 >>>