The Allometry of Seed Weight and Seedling Relative Growth Rate

Relative growth rates of plant species are often reported to decrease with increasing seed size. Since a general allometric relationship shows that relative growth rate decreases with increasing body size in animals and unicells, the seed sizerelative growth rate relationship may be a special case of a more general allometric relationship. In this paper, we analysed the allometry of seed weight and seedling relative growth rate in 204 species, based on seven published data sets, and compared our results to the allometric equation of animals. Seedling relative growth rate scaled significantly to seed weight in only three data sets. When points outside of the 95% confidence intervals of the individual regressions were removed, five out of the seven data sets exhibited significant negative correlations. Slopes varied from -0158 to +0 08 among data sets but an analysis of covariance showed that all data sets shared a common slope of -0 038. The amount of variance accounted for by seed weight varied from 68 to less than 1%. Plants and animals differed in their size dependence of growth but all plant relative growth rates closely followed the regression equation based on the animal data and all plant estimates fell well within the 95% confidence intervals of the animal regression. Despite the statistical difference in slopes, there was a general concordance of the plant and animal data, indicating a similarity in the allometry of growth rates. Key-words: Allometry, comparative ecology, relative growth rate, seeds, seed weight