Animals

How animals live

The giant panda has adapted its diet to bambooThe giant panda has adapted its diet to bamboo The process of evolution ensures that only living things that are suited, or adapted, to their environment will survive. An animal or plant that is poorly adapted to its surroundings soon loses out in the struggle for survival. Animals are adapted to three major features of their environment: the climate (including temperature and rainfall), the food sources available and the predators. The key features of an animal are that it has a body made of many microscopic cells and it gets its energy and nutrients by eating—that is, it takes in or consumes food. Animals can also move about for at least a part of their lives.

A sponge, a simple marine animalA sponge, a simple marine animal
A member of a new group of insects, discovered in 2001A member of a new group of insects, discovered in 2001

Number of species

Scientists have identified at least 2 million different kinds or species of animal, from tiny worms smaller than a comma, to huge elephants and blue whales. There are almost certainly at least the same number of species still to be identified—for example, insects and other small invertebrates in tropical forests yet to be discovered. The total number of animal species may be far higher: 10 million, or even more.

The study of animals is called zoology. The word from the ancient Greek words zoon, meaning "animal", and logos, meaning "knowledge". Zoology includes the study of the internal structure, behaviour, evolution, classification and geographical distribution of animals.
 

A honeybee colonyA honeybee colony 

Survival behaviour

To survive in the wild, an animal must find food and avoid predators. For some animals, the best way to do this is to live in complex social groups. A number of species of bee, for example, live in colonies. The members of the colony work together to provide shelter, food and protection for the colony, as well as raising the young. Other animals, for example, a tiger, lead a solitary way of life, but will group together to mate or raise their young. Most animal behaviour is directed towards increasing the chances of an animal’s survival in environment it lives in.

Long-eared jerboa, a desert animalLong-eared jerboa, a desert animal

Living in the desert

Life thrives in its greatest diversity in warm and moist or wet conditions, such as tropical rainforests and coral reefs. Places that are very cold or very dry provide the greatest challenge to animal survival. Yet some creatures can live in even the driest deserts. They include large animals such as camels and oryx, and smaller creatures like jerboas, lizards, scorpions and insects.



In hot deserts, smaller animals usually hide from the scorching sun by day and come out in the cooler night. They produce very little sweat, urine or other body liquids, thus saving valuable water.

Features of the camelFeatures of the camelThe camel is well adapted to desert conditions. It has wide, two-toed feet with soft pads that spread out, allowing it to walk easily on loose sand and not sink in. Its long eyelashes stop sand getting into its eyes. Its long legs keep its body 1 metre (3 feet) above the hot sand. It can go for two weeks without food or water. The body fat in its hump is used as an emergency food store, and can also be broken down by body chemistry to form extra water. 

Polar bearPolar bear

Living in polar regions

Only warm-blooded birds and mammals are able to live on land or in the air in the Earth’s coldest regions, the Arctic and Antarctic ice caps, our high mountainous terrain. Reptiles and amphibians would simply be too cold to move. Musk ox and polar bears have thick furry coats to keep out the chill, while penguins have several layers of dense feathers and a thick layer of fat under their skins.

Besides their furry coats, polar bears have thick layers of blubber beneath their skins. The pads of their paws are covered with small bumps to help them grip the ice.


WalrusWalrus The walrus dives in icy Arctic waters to find its food, mainly shellfish on the seabed. Under its skin, there is a fatty, blubber layer of up to 15 centimetres (6 inches) thick. The walrus’s limbs are adapted as paddles for swimming. Its long tusks act both as levers to pull shellfish off rocks and as ice-picks to haul itself out of the water.




Starfish and other seashore life at low tideStarfish and other seashore life at low tide

Living on the seashore

One of the most varied habitats is the seashore. The main change here is the twice-daily rise and fall of the tide. Animals such as worms, shrimp and shellfish are active only when they are covered by the seawater—whether it is day or night, winter or summer. Crabs and shellfish like limpets have strong outer cases to prevent them drying out at low tide and also being smashed by the waves. Soft-bodied worms and fish burrow in sand or hide under rocks for protection against winds and waves.


Survival in the deep oceans

Animals of the deepwater abyssal plainAnimals of the deepwater abyssal plainOne of the most constant habitats is the bottom of the ocean. It is always dark and cold, with few water currents. The main problem at great depths is the enormous pressure of the water. Certain species of deep-sea fish, starfish and sea cucumbers survive as their bodies contain no air spaces inside them. They would go soft and floppy (and die) if brought to the surface. 


Consultant:
 Chris Jarvis
 

To protect their almost hairless bodies from the hot African sun (when not submerged in water), hippos have a substance in their skins that forms a sunscreen. It also prevents the growth of disease-causing bacteria.

Temminck's coursers are shorebirds that seek out recently burnt grassy plains following wildfires. They feed on the insects that have perished in the fire.

Unlike seals and walruses, sea otters have no layers of blubber under their skins to keep them warm in the cold Arctic waters. Instead, they rely on air trapped in their fur to insulate their bodies. Oil spills can damage this fur, resulting in the otters' death.

A polar bear weighs about the same as a small car, and yet is able to walk on thin ice because its large feet help to spread its weight.

King snakes live in semi-arid regions of the American West. They are immune to the venom of rattlesnakes, and will kill and eat them.

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