Living things have relationships with one another and with their physical surroundings. Ecology is a branch of science that studies these relationships. It shows how much plants, animals, and other organisms nature depend on one another and on natural resources such as air, soil, and water.

Ecologists

Scientists who are interested in ecology are called ecologists. Ecologists need to know much about biology—the science of living things. They also must understand the sciences that deal with weather, climate, rocks, earth, soil, and water.

Ecologists may work in a laboratory or out in a natural setting. Laboratory experiments allow ecologists to study things under controlled conditions. For instance, plant growth can be watched as the scientist gives it different amounts of light and water. It is harder for ecologists to control conditions in a natural setting. They cannot make sunshine or rain. However, natural settings are useful because they are real. They show all of the different factors that make up life in a given community.

Plant and animal communities

The idea that plants and animals tend to group themselves into units called communities is basic to ecology. Certain animals and plants can share the same natural home; others cannot. Trees such as oak and hickory are found together in forests, but a fish and a camel would not be found in the same community. A fish needs a body of water, and a camel can survive in the driest of places.

Members of all communities compete for resources. Plants growing in dry soil compete for water. The trees of a dense rain forest compete for sunlight. Crops compete for both of these as well as for nutrients. Some members of a community may not survive the competition. Sometimes, however, community members change their behavior to reduce competition. Pumas, for example, roam widely while hunting but try to avoid the hunting territories of other cats. Bees cooperate and live together in a hive.

Ecologists have discovered that communities are born, develop, die, and are replaced in a regular, predictable pattern if natural processes are undisturbed. This pattern of change is called ecological succession. A small pond, for example, will gradually fill up with soil particles—silt and humus—until it is solid enough to support bog plants. Through the years more soil is formed until the bog becomes dry land that supports shrubs and trees. At each stage in this development, the natural community is different. It first includes fish and water plants, then animals and plants of swampy areas, and finally dwellers of dry land.

Ecosystems

A natural community and its environment—the living and the nonliving—make up an ecological system, or ecosystem. Every community takes vital materials from its surroundings and transfers materials to it. Raw materials and decay products are exchanged continuously. Thus, in an undisturbed area basic resources are sustained, never exhausted.

Ecosystems exist on many kinds of lands, in lakes, in streams, and in oceans. They generally contain many kinds of life. A cornfield, for example, contains more than just corn. It also includes smaller plant species, insects, earthworms, and many tiny organisms in the soil.

Each member of an ecosystem has a role to play—producer, consumer, or decomposer. Green plants are producers because they make their own food through a process called photosynthesis. Animals, including humans, are consumers because they eat plants or other animals. Bacteria and other organisms that cause decay are decomposers.

The sequence in which producers, consumers, and decomposers feed on one another is called a food chain. For example, a typical food chain in a grassland begins with grass (producer), which is eaten by a mouse (consumer), which is then eaten by a snake (consumer), which in turn is eaten by a hawk (consumer). Decomposers feed on dead plants and animals, breaking them down and returning nutrients to the soil so that new plants may grow. This starts the food chain over again.

The continued existence of an ecosystem involves a balance among its members. In a balanced ecosystem, the population of each species stays within limits. For example, carnivores (meat eaters) eat herbivores (plant eaters) and therefore keep the herbivore population under control. Without carnivores, the herbivore population would soar, leading to overgrazing. Eventually there would not be enough plants for the herbivores, which would then starve and die as a result.

Importance

Knowledge of ecology is probably more important today than at any other time. Ecologists have seen what happens in nature when a population of animals increases so much that the environment cannot support it. With the world's human population growing at a tremendous rate, people are facing similar problems. Scientists must now work to increase food supplies; find new, safe sources of fuel and power; and conserve the Earth's natural resources. By good management of the Earth and by caring for the animals and plants that share the planet, people can make sure that its natural riches and beauty are preserved for future generations. (See also conservation.)