other. The most obvious heterotrophs are impressive beasts such as bison, giraffes, lions, and us, but the vast majority are unobtrusive organisms such as fungi and microbes that get their energy from decomposing dead material. The worms that eat us when we die are above us in the food chain. In fact, ecologists now speak of food webs rather than chains, because in any place most species eat several different kinds of plants, animals, or both and in turn have to avoid several different predators or parasites. Food chains can become loops—the worms might get you in the end, but in the meantime if you eat a chicken that feeds on worms, you can reestablish your trophic superiority. A complex network of links is needed to describe who eats whom.

One way to create diversity is to put another link in the food chain. But as a biological job creation scheme, such a ploy is not very effective. Most food chains are only four or five species long. The ecologist who worked out why they are not longer was a protégé of Hutchinson—Ray Lindemann. Hutchinson and Lindemann were among the first scientists to think about how the patterns shown by a group of different species living in the same place, called an ecological community, could be the result of the way that energy flowed through them—“If the community is an organism, it should be possible to study its metabolism,” Hutchinson once wrote. And before he moved to Yale to work with Hutchinson, Lindemann spent five years studying a Minnesota lake called Cedar Creek Bog, plotting the links between plants taking up energy and materials, consumers eating plants and one another, and decomposers feeding on corpses and recycling their nutrients to plants. In the process, Lindemann realized that, in energetic terms, living things are leaky vessels and that the loss of energy as living matter passes up the food chain can explain the pattern of declining numbers and diversity.

For starters, Lindemann reasoned, the laws of thermodynamics prevent energy from being perfectly converted from one form to another. But there are other leaks besides this one. Much of the energy a plant or animal obtains will be used up before it is eaten, and much of it will be converted into tissues that are indigestible to its predator, although not to microbes in the predator’s gut or the soil. A large portion of the energy entering one level of a food chain is lost. All flesh is



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement