Maintenance Maintaining a healthy body is usually possible only in a narrower zone than that in which survival is possible 3. Growth Often limited to a relatively narrow zone of benign conditions surrounding the optimum 4. Reproduction Usually the narrowest zone, close to the optimum, and the only conditions where all four functions can be done successfully Dominant mechanisms for responding to the environment and for allocating resources are often correlated with the shapes of the response curves. Conformers tend to have tall, narrow response curves with acute peaks and spanning only a small part of the gradient. Homeostatic organisms tend to have low, broad, flat-topped response curves spanning a large part of the environmental gradient.
Regulators lie somewhere on a continuum between conformer and homeostasis.
Dominant response modes are also often correlated with environmental grain. Conversely, homeostatic organisms are often successful in fine-grained situations, performing well under a broad range of conditions. Regulators are usually intermediate. The concept itself has evolved over the decades, encompassing at least three major ideas. This original concept arose directly from extensive physiological studies, usually in the laboratory, of individual's response curves and especially of their limits of tolerance.