The Community Ecology (1962)

In any human community, we find people with certain kinds of jobs or roles. Policemen and housewives, clerks and children, students and grossers. Each has a special job or place in the community. Each person is part of his particular community because he depends on the others in some way. Each has a certain niche in his community. Natural communities too are organized according to the niches of the many different living organisms. Take the pine forest for example. Each organism in the community occupies a niche according to the role it plays forming what the ecologist calls a biotic community. The primary source of energy on Earth is the sun. Green plants convert the sun's energy into the organic matter that all organisms must have to live. In most biotic communities, certain plants provide the main food energy and set the character of the community. Such plants are called the dominant plants. Here the pine trees are the dominant plants. They determine what kinds of other organisms can live here. The pine trees are called the primary food producers. But other green plants in this community also serve as food producers. All the other organisms, large and small, are consumers that depend on the food producers. Here is one kind of plant eater or herbivore. Herbivores are specially adapted for feeding on plants. Herbivores are eaten in turn by other animals, the primary carnivores. The aphus lion competes with a ladybird beetle for a diet of aphids. Primary carnivores serve as food for secondary carnivores, such as this bird. Carnivores are usually larger and fiercer than their prey and fewer in number. Some animals occupy more than one niche. Bears, for example, can be either herbivore or carnivore depending on whether they find berries or fish to eat. Some organisms live by feeding on others without killing them. This is the niche of the parasites. Almost every living thing is subject to some form of parasite. All organic matter, living or dead, eventually serves as food for some organism. Dead organic matter, such as this fallen tree, is being eaten by scavengers. Termites occupy the niche of the scavenger in this rotting log. In the log live other scavengers, ants and millipeds, which feed on dead organic matter in the vicinity. The activities of these scavengers break down the log for organisms of another niche, the decomposers. The decomposers may be bacteria, yeasts or this mold. These organisms convert organic matter into simpler substances which can be used by green plants in their growth and in the making of food, thus making it available for another food energy cycle. Other communities may have different kinds of organisms, but the basic niches always remain the same. Grass is the dominant food producer here, giving the community its name, the grassland. Then what eats the grass? Cattle have replaced the bison that were once the largest herbivores on the grasslands of North America. Among the smaller herbivores are the insects. It takes a great many herbivores such as grasshoppers to feed one primary carnivore such as a bird. Each niche contains a larger number of individuals than the niche that eats it. This numerical relationship is called a pyramid of numbers. Grass is eaten by the grasshopper. The grasshopper is eaten by the frog. The frog is eaten by the snake. The snake is eaten by the hawk. This is called a food chain. Because the hawk has no larger predators, it is called the top carnivore in its food chain. There are many food chains in a community. Here is another. Grass is eaten by the rabbit. The rabbit is eaten by the fox. Because it eats other animals, too, the fox is a link in several food chains. The fox is a top carnivore in this food chain. Yet, it is attacked by organisms of another niche, the parasites. The complex of all the food chains in a community is called a food web. Since there is dead organic matter, we know there will be scavengers. Flies and beetles occupy that niche here. Bacteria and fungi occupy the niche of decomposers. They convert the organic matter into substances that green plants can use as food, forming the basis for the cycle of matter and energy of the community with its many niches and its food web. Here on the California coast is a different community, the intertidal community. Let us see how the niches are filled here. We can begin by asking the ecologists questions. What is the primary food producer? Is it the muscle? Is it the starfish? Is it the barnacle? Of all the organisms that together form this community, which are the herbivores? Which are the carnivores? Which are the scavengers? The primary food producers here are microscopic single-sellled plants called algae. Feeding on algae are myriads of tiny copapods. They occupy an important niche. Can you name it? Copapods serve as food for small fish. The niche. Smaller fish are eaten by larger fish. The sea anemone is another kind of secondary carnivore. The dead fish is eaten by the crab. What niche does the crab occupy? What place does the octopus have in its food chain? And what eats the seagull? The dead seagull is eaten by scavengers. Most biotic communities are complex. Yet in any community the same questions can be asked. What are the primary food producers? What niche does each organism occupy? You can ask these questions wherever you are. Whether you are in a desert, whether you are in a tropical rainforest, or whether you are in the community where you live,