ADAPTATIONS FOR EATING

All animals need food to survive. Animals eat plants, other animals, or both plants and other animals. Animals that eat plants are called herbivores. Zebras, cows, and moose are herbivores. Animals that eat other animals are called carnivores or meat-eaters. Dogs, lions, and sharks are carnivores. Animals that eat both plants and animals are known as omnivores. Bears are omnivores.

Biologists describe the relationships between animals in a habitat and the foods they eat as a food chain. Technically, a food chain involves the flow of energy from the sun to green plants to animal consumers. For example, a simple food chain in a meadow links the grasses, the deer that eat the grasses, and the wolves that eat the deer. Sometimes, many kinds of animals and plants are involved in complex networks of food chains. Such networks are called food webs.

Most animals eat a variety of foods. For example, pigeons eat fruits, grains, and nuts, and they sometimes feed on insects, snails, and worms.

Some animals eat only a few foods. A snail called a cone shell preys only on a single species of marine worm. Several kinds of snakes eat only slugs or other snails. Hummingbirds and honey possums live on the nectar of flowers. A sapsucker drills holes in trees and eats the sap that flows from the holes. The koala of Australia dines on the leaves of eucalyptus trees.

Filtering mechanisms. Huge numbers of tiny organisms called plankton float or swim slowly near the surface of oceans, lakes, and other bodies of water. Plankton make up a part of an important food chain in the ocean. Plankton are too small to be captured individually by animals that feed on them. Some animals, such as barnacles, sweep water past themselves while straining out the tiny plankton, which are thereby captured. This process is called filter feeding.

Baleen whales are probably the best-known filter feeders. These animals, which do not have teeth, feed by gulping huge mouthfuls of water containing plankton, small fish, and other marine organisms. They then force the water out of their mouths through a series of strainers called baleen. The food is captured on the baleen and then swallowed. A baleen whale can consume as much as 4 short tons (3.6 metric tons) of food a day.

Teeth and jaws. Many animals eat food that they need to tear into pieces small enough to be swallowed and digested easily. Teeth and jaws are adaptations for tearing food. Teeth may also be used to kill prey. Teeth are adapted for the particular type of food an animal eats. Deer, giraffes, and other herbivores have teeth with broad surfaces for grinding grasses and plants into small bits. The powerful front teeth of beavers enable these animals to cut down trees for food and shelter. Lions have razor-sharp canine (pointed) teeth for killing and then tearing prey.