Drawing On Science
A few years ago, when I was younger (okay so it’s more than a few years) I bought a book on nature. In fact I had to send for it by mail because it was ttbsol (=the time before shopping on line. If you think this is bad, you should see the shorthand kids like my niece, Jessica, uses when “talking” on-line.) On the first page of this book was written, “To understand nature is to gain one of the greatest resources of life.” This is a quote by the naturalist John Burroughs. It is a statement that, today, is very important. Think about air pollution, water quality, global warming, and garbage disposal. The idea for this week’s column came to me when I found out that Jessica was studying food webs in school. I immediately thought “ecology.”
One of the best ways to understand nature is to have some knowledge of the science of ecology . The word comes from the Greek words oikos meaning “house” and logy, “the study (science) of.” Ecology, then, is defined as the study of the house. The house, of course, refers to our planet. Ecologists study groups of organisms in different natural settings. Organisms having the same structure belong to the same species . A species makes up a population . Different populations of species make up a community and a community is part of an ecosystem . Ecosystems (deserts, forests, lakes, oceans, etc.) also include the non-living things such as rock, water, and soil. Both the community and the non-living things make up an environment . The special place where an organism lives is called its habitat . All ecosystems make up the biosphere .
You walk along the shore of, say, Dead Horse Bay (just west of Flatbush Avenue right off the Marine Parkway Bridge) and you find razor clam shells. Then you find some bay scallop shells and a few shells of the ribbed mussel. Here and there are scattered pieces of different types of seaweed such as sea lettuce. There are also a large number of different plants including bayberry and pokeweed. All of these populations make up a community. This community is part of the marine ecosystem we call Dead Horse Bay.
Every organism has a part to play in a community. This role is called a niche (nitch). Plants for example are the producers . They make their own food using the sun’s energy. Some ants carry away dead insects and other dead things. They are scavengers . Wolves help keep the population of deer from growing too large. They are predators . Bacteria are decomposers , breaking down dead organisms into many substances. These substances, then, are recycled.
Imagine this: a field mouse is quietly feeding on some grass in a meadow. A few feet from the mouse a garter snake tastes the air moving closer to the mouse. In the sky above a Red-shouldered hawk spots the snake and begins its dive to obtain its dinner. On the banks of a nearby pond a grasshopper is chomping away on leaves of a shrub. A hungry bullfrog slowly makes its way nearer to the grasshopper getting its tongue ready for the strike. But an equally hungry Screech owl has it eyes on the bullfrog. Some distance from the pond a chipmunk is busy eating grass seed for lunch while a hungry fox waits for its chance to pounce on it. These are examples of food chains (see Fig. 1). Each organism in the food chain occupies a given trophic (TRO-fik =nourishment) level . Plants occupy trophic level one. They are producers and have the largest population. Animals are the consumers because they must obtain their food by eating another food source. Those that feed on plants occupy the second level and are known as primary consumers or herbivores (HER-buh-vorz). Animals that feed on herbivores occupy the third level and are known as secondary consumers or carnivores (CAR-nuh-vorz). Carnivores feeding on other carnivores occupy the third level and are known as tertiary consumers . There may be a fifth level and so on. There are, however, ultimate consumers , which occupy the highest level. These are the decomposers. But a food chain is too simple to really represent what is going on. Many organisms feed on more than one type of food so a food web is more realistic (see Fig. 2). A food web shows how animals may belong to a number of individual food chains within a food web.
As food energy is passed from one level to another, the amount of energy available decreases. This is true because each animal uses some of the energy to keep healthy. So what is left is passed on to the animal that eats the one before. This energy transfer is best shown in a food pyramid (Fig. 3). The base of the pyramid is composed of producers and has the greatest amount of energy. As stated before it is also the largest population. As we move up the pyramid the amount of energy decreases. Note also that the number of individuals in each population decreases. The topmost consumer ends up with the least amount of energy and the smallest population.
In Fig. 1 what would happen if the grasshoppers in the food chain were to disappear? (Hint: think of ‘populations’).Would the same thing happen if they disappeared in the food web? If the grasshopper population suddenly increased, how would it affect the food web?
Questions? E-mail Steve: Drawingonscience@aol.com