FIG. 1.20 Ecological relationships. (a) The trees in a rain forest all require water and nutrients. Neighboring plants compete for the limited supplies of these materials. (b) Plants provide food for many animals. Leaf-cutter ants cut slices of leaves from tropical plants and transport them to their nests, where the leaves grow fungi that the ants eat.

Sources: a. Louise Murray/Getty Images; b. Gail Shumway/Getty Images.