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In even—aged monocultures, distributions of seedling mass shift from symmetric to right—skewed as plants grow. One explanation for the shift is that numerous small individuals and few large ones reveal underlying dominance and suppression caused by depletion of resources. A second explanation is that the asymmetry represents a shift from normal to lognormal mass distributions because of variance in exponential growth rate. As a consequence of the first mechanism but not the second, the presence of resource depletion should increase both the skewness and the variance of distributions of individual plant mass. Even—aged populations of the prairie grass Festuca paradoxa were grown in the greenhouse for 44 d with and without competition (dense flats or one individual to a container), and with and without augmented nutrients. At each harvest, plants grown densely were smaller than isolated plants, demonstrating that resource depletion occurred. Distributions of mass of isolated plants skewed first and remained more highly skewed throughout the experiment. At a given mean mass, the standard deviation of mass for crowded and isolated plants did not differ. At a given mean mass, the skewness of mass for crowded plants was not greater than for isolated ones. The second explanation is supported, and shifts in distribution shape can be attributed to growth alone, in the absence of dominance and suppression. Competition in this case did not promote skewing but actually retarded its appearances. Consistency of these results with previous findings is discussed.

The number of flowering stems for 82 species on a transect 2 x 400 m was counted twice weekly during 1978 at Tucker Prairie, Callaway County, Missouri, USA, a tall—grass prairie remnant. Phenological curves (number of flowering stems vs. day of the year) are narrower (smaller standard deviations) for wind—pollinated species than for insect—pollinated species. Symmetry (g1) does not differ significantly for wind— and insect—pollinated species. The curves are largely either symmetric or begin abruptly and end gradually (right—skewed). Overlap, measured as the fraction of the area under the curves occupied by two or more species, does not differ significantly for wind— and insect—pollinated species, among 20 groups of five randomly drawn species. Dates of peak flowering are distributed randomly over the season (May to November 1978) and their distributions do not differ for wind— and insect—pollinated species. Dates of peak flowering are also randomly distributed for grasses, legumes, and composites considered separately. Thus, although species with different pollination modes show different shapes for phenological curves, the species aggregated into the community do not have ensemble patterns of temporal dispersion or overlap and cannot be distinguished from a random collection.