Figure 1. Levels of biological organization. The ecosystem level incorporates the interactions among organisms and their abiotic environment.

Figure 2. (a) A generalized diagram of an ecosystem showing trophic interactions. (b) Charles Elton's pyramid of numbers. The number of individuals in each trophic level is represented by the size of the bar. Both of Elton's findings are evident in this figure: The number of individuals decreases moving up the food chain, and food chains are rarely longer than four to five levels.

Figure 3. (a) Global distributions of terrestrial biomes. (Adapted from Bush MB (1997) Ecology of a Changing Planet, by permission of Pearson Education, Inc., Upper Saddle River, NJ.) (b) The relationship of terrestrial biomes to average temperature and total precipitation. (Adapted from Whittaker RH (1975) Communities and Ecosystems, by permission of Pearson Education, Inc., Upper Saddle River, NJ.)

Figure 4. Energy budget for the Earth system. Numbers represent percentages of the energy received as incoming solar radiation. (Reprinted with permission from Chapin et al. (2002) Principles of Terrestrial Ecosystem Ecology. Springer-Verlag, New York.)