Higher-level Phenomena Research Articles

Mechanistic Approaches to Community Ecology: A New Reductionism

Mechanistic approaches to community ecology are those which employ individual— ecological concepts—those of behavioral ecology, physiological ecology, and ecomorphology— as theoretical bases for understanding community patterns. Such approaches, which began explicitly about a decade ago, are just now coming into prominence. They stand in contrast to more traditional approaches, such as MacArthur and Levins (1967),which interpret community ecology almost strictly in terms of “megaparameters.”. Mechanistic approaches can be divided into those which use population dynamics as a major component of the theory and those which do not; examples of the two are about equally common. The first approach sacrifices a highly detailed representation of individual— ecological processes; the second sacrifices an explicit representation of the abundance and persistence of populations. Three subdisciplines of ecology—individual, population and community ecology—form a “perfect” hierarchy in Beckner's (1974) sense. Two other subdisciplines—ecosystem ecology and evolutionary ecology—lie somewhat laterally to this hierarchy. The modelling of community phenomena using sets of population-dynamical equations is argued as an attempt at explanation via the reduction of community to population ecology. Much of the debate involving Florida State ecologists is over whether or not such a relationship is additive (or conjunctive), a very strong form of reduction. I argue that reduction of community to individual ecology is plausible via a reduction of population ecology to individual ecology. Approaches that derive the population-dynamical equations used in population and community ecology from individual-ecological considerations, and which provide a decomposition of megaparameters into behavioral and physiological parameters, are cited as illustrating how the reduction might be done. I argue that “sufficient parameters” generally will not enhance theoretical understanding in community ecology. A major advantage of the mechanistic approach is that variation in population and community patterns can be understood as variation in individual-ecological conditions. In addition to enriching the theory, this allows the best functional form to be chosen for modeling higher-level phenomena, where “best” is defined as biologically most appropriate rather than mathematically most convenient. Disadvantages of the mechanistic approach are that it may portend an overly complex, massive and special theory, and that it naturally tends to avoid many-species phenomena such as indirect effects. The paper ends with a scenario for a mechanistic-ecological utopia.

Combination bands of even order: masking effects and estimations of level of the difference bands (f h -f 1 ) and 2(f h -f 1 ).

The levels of the difference bands, fh − fl and 2(fh − fl), generated by a pure tone and a narrow band of noise, have been estimated in a manner reported in previous papers (Greenwood, 1971a, 1972a, 1972b). Results and conclusions follow: (a) Combination bands of the form fh − fl and 2(fh − fl) vary in level as functions of stimulus parameters in ways very similar to the variation in level of the difference tone, fh − fl, produced by tonal primaries, as measured by cancellation techniques. Difference band levels are rather insensitive to increases of primary frequency ratio in the ranges explored (about 1.35–1.85). Difference band level obeys different functions of primary intensity depending on whether one or two, and whether the upper or the lower, primaries are varied. When the lower primary level is varied alone, square-law behavior is observed, in agreement with Goldstein (1967) and with Zwicker (1955); when the upper primary or both primaries vary, curves depart from square-law behavior in near agreement with Goldstein. Békésy's 1934 observations (1960) and Wenner's (1968) results suggest a conceivable explanation that might resolve some apparent discrepancies among results of Goldstein, Zwicker, and this paper when both primaries vary. (b) At primary levels exceeding about 60 dB SPL, combination tones of the form n(fh − fl) and combination tones of the form (n + 1)fl − fh will exist simultaneously, and since they lie in the same frequency region they will interchange places, with varying interactions, as primary ratios are varied—producing perceptual effects relevant to higher-level phenomena of consonance generally and to the beats of mistuned consonance specifically.