Nature of size-number trade-off:: test of the terminal-stream-limitation model for seed production of Cardiocrium cordatum

We tested the prediction of the terminal-stream-limitation model using Cardiocrium cordatum. This model predicts that the total offspring mass increases with offspring number, whereas it decreases with offspring size, because the loss of resources via maintenance respiration decreases with offspring number but increases with offspring size. We traced the growth curve of seeds and harvested seeds when they matured. The maximum gross growth rate of a seed had a strong positive effect on final seed dry mass, whereas the respiration cost had a strong negative effect on such mass. The total seed mass produced by a plant decreased with (or was independent of) an increase in the mean seed dry mass of the plant, whereas it increased with an increase in the number of seeds produced by the plant. An increase in seed number resulted in a decrease in the loss of resources due to respiration during seed growth, whereas an increase in the mean seed dry mass did not result in a decrease in the loss of resources due to respiration. Thus, we concluded that these results are consistent overall with the prediction of the model and that an increase in seed number rather than an increase in individual seed size is advantageous in terms of resource use efficiency.