Patricia Ryan, age 12, of Philadelphia, Pennsylvania, for her question
What do they mean by the food chain?
The young science of ecology promises to be the most important field of our day. One of its aspects concerns food. And thoughtful scientists are concerned about increasing human food supplies to keep pace with our increasing population. Their plans must start with ecology.
Suppose your diet includes a lot of tuna fish and you like it. As you grow, this nutritious protein food, with others, will add pound by pound of healthy bones and muscles to your body. A vital diet problem is solved and many people do not bother to think beyond this point. However, a wide awake young student may wonder about the background story of those cans of meaty tuna. Probing the story step by step takes us out of the store where the tuna is bought far from the dinner table to the very ends of the earth. Along the way we accidentally learn about a food chain. And our eyes may pop when we discover that this is just one of countless interlocking food chains in the world of nature.
Our sample food chain is somewhat like a pyramid with a tuna eating person at the top. The lower levels involve larger and still larger numbers of living things. Since we started our tuna diet in terms of poundage, let's figure the stages to the pyramid in weight ratios. A person requires ten pounds of tuna to produce one pound of usable food for his body. The big tuna fish of the deep ocean must eat 100 pounds of smaller fishes to get ten pounds of usable food.
Most of the tuna's diet of smaller fishes dine on a mixture of small and microscopic animals and plants. This floating seafood salad is called plankton. The assortment of little fishes on the tuna's diet must eat half a ton of plankton to get 100 pounds of usable food. When we trace the pound of food our body could use all the way back to the base of its food chain pyramid, we find that it was built stage by stage from the 1,000 pounds of food produced by the marine plankton.
Similar food chains operate to support the teeming populations of living things on the land. Different pyramids are built on the ecology of various locations the different conditions and living things found in tropics and polar regions, forests and deserts. Our tuna pyramid involves countless marine dwellers and interlocks with countless other marine food chains. All the food chains of the earth are interlocked directly or indirectly in a vast, complicated web of give and take.
Each food chain requires tremendous activity and energy and the base of. the pyramid shows us the source of its power. Plants use solar energy to convert simple chemicals into more complex chemicals. The basic ingredient in plankton is the algae plant life that feeds the microscopic animal life. On land, plant greenery feeds the zebras that provide meat for the lion. Everywhere in nature, the web of interlocking food chains is generated by the radiant energy of the sun.
Ecologists study food chains that support the specialized plant and animal com¬munities of various locations. They view each stage of the eating game as a conver¬sion of solar energy into more concentrated food elements. The life forms vary but the patterns and ratios do not. At each stage of a food chain, 90 per cent of the energy is used to remodel simpler chemicals into more concentrated food elements.