What Ecologists Do (1971)

Once there were bald eagles in many parts of the United States. But now most of them are gone. Their nests are empty. Scientists called ecologists wanted to learn why. They found that eagles eggs were not hatching. The ecologists learned that this was caused by certain poisoned sprays used to kill insects that eat important plants. The poisons don't break down. So every time a field was sprayed, the amount of poison in the soil grew larger. Animals living there picked up some of the poison. Some of the remaining poison ran off into streams and lakes and got into the organisms or living things there. Even the smallest organisms took up the poison. Each time a small fish ate one of these smaller organisms, it took almost all the poison from it into its own body. And each fish ate many of the smaller organisms. When crayfish or larger fish ate the smaller fish, they got the poison. And when even larger fish ate the crayfish, smaller fish, or poisoned insects that fell into the water, the poisons were passed on. Since the poisons did not break down or pass out of the animals bodies, and since big animals ate many smaller ones, the concentration of poisons got stronger and stronger in each larger animal. Eagles eat mostly dead fish, which usually have the most poison. As a result, the concentration of poisons became very high in eagles. It wasn't high enough to kill the big birds, but it was high enough to keep their eggs from hatching. If this continues, there soon may not be any more eagles. We will not only lose our national bird, but also a way of removing dead animals. And if it happens to the eagle, couldn't it happen to other animals, including man? Might not the death of the eagle tell us that something is wrong with the balance of nature? In order to find out, we must look at how organisms act on each other and their surroundings, called the environment. This is what ecology is all about. How living things act or depend on one another and on the environment. And ecologists are scientists who study these relationships. Ecologists need to know many things, like what kinds of organisms are in an environment, how many of each kind there are, and how much these numbers change. Ecologists also must learn how big and how old the organisms are. They need to know about the life of each kind of organism. What they eat, how they move, how many young they produce each year, how fast they grow, how long they live, what other organisms they interact with or depend upon, and what environment they like or can live in. Ecologists also need to know something about the environment. It takes many ecologists doing different things to obtain all this information. And it's not easy. For example, ecologists would like to gather up all the organisms in an environment, find out what they are, count them, and measure them. But they can't. Why not? There are simply too many places in an environment where organisms can live, and too many living things in each place. Also, many animals move fast or are hard to catch. And finally, if ecologists gathered up all of the organisms, they would destroy the system they are studying. Instead, ecologists collect organisms from several small areas in different parts of the environment, and then guess or estimate how many are in the entire environment. This is called sampling. One way of sampling the organisms on land is to mark off certain sized areas in different places, and then collect, identify, count, and measure all the organisms in these areas. The small plants can be cut down and preserved, but the large trees are measured and identified where they are. Most animals are simply picked up, sifted from the soil, or caught in nets. But how can ecologists collect bigger or faster moving animals? This ecologist is setting out a wire trap with a funnel-like door, so a snake can easily get in, but can't easily get out. A screen fence guides the snake into the trap. Ecologists use different kinds of traps. This one has a hinged lid that closes when an animal moves the trigger. Traps work better when something is used to attract the animals to them. What could be used to attract animals? Weighing and measuring an organism also gives some idea of how old it is. How else can ecologists find out how old an organism is. The age of a tree, for example, can be determined by drilling into the trunk and removing a small sample or core. There is usually one line or growth ring in the wood for each year the tree has been alive. By counting the lines, ecologists can tell about how old the tree is. Similarly, each ring or line on the plate of a box turtle shell is usually equal to 1 year's growth. Aside from determining the age, size, number, and kind of animals captured, ecologists often mark and release the animals they catch. When the same marked animals are captured again, it gives some idea of how good the trapping is. Ecologists also need to know about the life cycle or life history of the organisms they study. They can start by reading what other scientists have already written about these organisms. But sometimes there isn't enough written information, and the ecologist must either watch the organisms in nature or grow them in a laboratory. If he raises them in a laboratory, he can change the environmental conditions to see how this affects each stage of the organism's growth. For instance, seeds can be heated or cooled for different lengths of time to see how well they grow at different temperatures. Or animals can be placed in a container where they are given a choice of foods or of temperatures to see which they like best. Watching animals in nature can be difficult and can take lots of time. So ecologists often use other methods. For example, they can find out how much food and what kinds of food an animal eats by looking in the stomachs of many individuals. They can find out where an animal goes by attaching a spool of thread to the animal. The thread unwinds when the animal moves leaving a well-marked trail. Or they can attach a small radio transmitter to an animal. The radio sends back beeps which can be picked up by a radio receiver with a directional antenna. When the antenna is turned toward the radio transmitter, the beeps get louder. By moving the antenna around, an ecologist can tell where the animal is. Ecologists must also study the non-living things and conditions in an environment. These non-living things include air, soil, and water. Ecologists use different instruments to measure conditions of these non-living things. For instance, thermometers tell how hot or cold the air or water or soil is. And chemical tests can tell what kinds of substances are in the air, soil, or water. When ecologists study the relationships between organisms and their environment, they must include man. Because of all living things, man has the greatest power to change his environment. Almost everything that man does changes the environment environment and how to correct some of the mistakes man has already made. For example, the water hyacinth was brought into the United States because it's pretty. But it grew and spread so rapidly that it filled many rivers and lakes in the South. Chemicals to poison the plants are now being sprayed on lakes and rivers. But this can hurt other organisms. Might there not be a better way of getting rid of water hyacinths? Some ecologists have suggested bringing in manatees and other water animals to eat the hyacinths. But maybe these animals will become pests themselves. Other ecologists have suggested gathering the hyacinths with big machines and feeding the plants to cattle. Both ways are now being tried in certain areas to see which might be best. Ecologists also play an important role in fighting man-made pollution. Pollution is usually thought of as so much of some chemical substance in the air, water, or soil that it is harmful to organisms in that environment. Ecologists can tell us if water is polluted by finding out what organisms are in it. By pouring harmless colored dye in a polluted stream, they can find out where the water goes, even if it goes underground, because the dye will show up when the water comes back out of the ground. This helps ecologists locate the source of water pollution, so they can help stop it. The work of ecologists is important to the health and survival of all living things on Earth, including man himself.