Most species of higher plants have qualitatively similar resource requirements for growth and reproduction (Chapin et al., p. 49, this issue). They differ, however, in the way they use resources to carry out three essential functions-reproduction, defense against herbivores, and growth. Each of these functions requires a complex set of resources, including carbon, nitrogen, and phosphorus, that make up the structures (leaves, stems, fruits, roots) associated with different functions. Variation in resource allocation occurs through differences in the chemical composition of structures, the relative mass of different structures or organs, and the relative numbers of different structures a plant produces. This variation occurs within individuals through time, within and among populations, and especially among species (Figure 1).
Examinations of this variation cross many fields of ecology, including physiological studies of the relationship between structure and function in plants, biochemical studies ofFakhri A. Bazzaz is professor of biology in the iello is scientific coordinator of the Jasper Ridge Biological Preserve of Stanford University, Stanford, CA 94305. Phyllis D. Coley is assistant professor in the Department of Biology, University of Utah, Salt Lake City, UT 84112. Louis E Pitelka is project manager in the Ecological Studies Program, Electric Power Research Institute, Palo Alto, CA 94303. ? 1987 American Institute of Biological Sciences. Resource allocation to plant structures of different composition, size, number, and function varies within and among populations and especially among species.
