Some Contributions of Physiological Ecology to Plant Population Biology

Abstract

Information on the physiological responses of plants, particularly photosynthetic capacity, can be utilized in an integrative manner to predict potential success in habitats where resources are closely defined. This approach has been utilized primarily for interspecific and interpopulation comparisons. Similar studies of withinpopulation physiological variability, which will be demanding, are needed to link the approaches of physiological ecology more closely with those of evolutionary population biology. Physiological ecology is the study of the physiological mechanisms that adapt organisms to their environment. Once understood, the operation of these mechanisms can be,quantitatively related to the environment and hence predictions can be made about the success of a given phenotype in any environment. In the context of population biology the result of a selection experiment in a specified environment could be predicted as indicated in Figure 1. Physiological ecology offers population biology some understanding of the what and why that goes on in the selection environment that is more often than not treated as a black box by population biologists. Unfortunately the physiological ecologist rarely follows through on his predictions and actually tests an ending array of phenotypes for heritable physiological characteristics. Attention is instead focused on learning about the physiological characteristics of the starting array and how these relate to the existing environment. Generally, predictions rather than tests are made of the possible results of new selection. Physiological ecologists study many problems of common interest with population biologists, such as adaptation along environmental gradients, adaptation to fluctuating environments, evolution of optimal forms, and niche separation. The approaches utilized in these studies illustrate more specifically how physiological ecologists contribute to the objectives of population biology. The photosynthetic capacity of plants has been intensively studied by physiological ecologists because this process is so fundamental that the linkage to reproductive success is fairly direct. Thus many of the examples that I give center on the varying photosynthetic capacities of plants. Photosynthesis provides the energy for organisms to engage in the competitive process of gathering water, light, and nutrients. These resources are in turn 1 Appreciation is expressed to the National Science Foundation for the support of many of the studies described here. 2 Biological Sciences, Stanford University, Stanford CA 94305, This content downloaded from 207.46.13.111 on Sun, 07 Aug 2016 06:55:08 UTC All use subject to http://about.jstor.org/terms 270 SYSTEMATIC BOTANY [Volume 1