The Variety of Animal Life
Edward R. Ricciuti
Groups of animals may share some traits, yet every kind of animal has its own life-style and way of surviving. Sometimes the traits that make the living patterns different are very small; the great blue heron and the little blue heron are an example. They both are long-legged birds that wade into water to stalk small creatures, such as fish and frogs. They both live in marshes or other wetlands. However, the great blue heron is about twice the size of the little blue heron. The difference in size means that they feed in the same place, in a similar manner, but at different depths.
Each kind of animal is suited to living in a particular kind of environment, or habitat. An animal fits into a niche within its habitat -- that is, it has a specific role within its community. Wetlands, such as marshes, are the habitat of herons, while their niche is that of a bird that wades to catch small water animals.
The heron's behavior and body structures enable it to survive within its particular habitat and niche. While wading, a heron will freeze its movements; motionless, it looks for a fish or a frog. When the heron sees its prey, it quickly extends its long neck and with its bill seizes the startled prey.
The climbing perch, an Asian fish, has another type of life-style. It lives in small ponds that sometimes dry up during times of drought. When this happens, the perch behaves in an unusual way for a fish: It creeps over the ground to another pond that still holds water. The climbing perch can do this because it has strong, flexible fins that act almost like legs. It also has a lunglike organ that allows it to breathe air as it travels out of water and over land.
The traveling behavior, fins, and air-breathing organ of the climbing perch are like the heron's long legs and hunting behavior. They are all changes, or adaptations, of a living thing geared to a particular way of life. Every animal has its own special adaptations that improve its chances of survival.
Animals do not adapt on purpose; they adapt by chance. The adaptation of the giraffe's ancestors is an example. It may appear that the ancestors of the giraffe grew a long neck so they could feed on leaves in trees; however, that is not the way it happened. Millions of years ago, a giraffe ancestor was born with a neck that was longer than the neck of the other animals in its group. It was not much longer than the neck of the others, but long enough so the animal could reach higher for food than the rest of the group. All the offspring of the long-necked ancestor had the same trait. Because more food was available to them, the long-necked animals had a better chance of surviving. As time passed, they survived in greater numbers than their short-necked relatives. Slowly, the long-necked animal developed into the giraffe of today.