On the quantitative theory of reproductive effort in clonal plants: Refinements of theory, with evidence from goldenrods and mayapples

Abstract

Recently I proposed a quantitative theory which predicts the partition of resources between vegetative growth and seed production in highly rhizomatous clonal plants (Armstrong 1982, 1983). My basic premise was that this partition should be controlled by basic geometric properties of clonal growth. My conclusions were that the ratio of resources expended on seeds and rhizomes should be relatively constant in time and space, and that the value of this ratio should be predictable from a knowledge of the allometric relationships among certain morphological characters. In the present paper I first refine this theory to yield explicit ramet-level predictions directly applicable to clonal species with densely-packed canopies. These predictions are then tested using observations on goldenrods (Solidago altissima) and mayapples (Podophyllum peltatum). In the Solidago studies, the ratio of infructescence weight to total rhizome weight was found to be asymptotically constant for the larger ramets in a clone, confirming an important prediction of the theory. A second prediction of the theory, that the ratio of infructescence weight to total rhizome weight should be constant across clones, was not confirmed using the goldenrod data. This observation may simply be due to measurement biases. An alternative hypothesis is that the prediction of this theory constitute an r-limit strategy, and so are applicable only in the limit of density independent growth. Data from Sohn and Policansky (1977) on mayapples support this latter interpretation.