Fruit to flower ratios and trade-offs in size and number

Summary Hermaphroditic flowering plants commonly produce many more flowers than fruits. To interpret this observation, I suggest an explanation based on trade-offs occurring between the size and the number of flowers and fruits that mature when resources are limiting. I make this suggestion concrete with the aid of a phenotypic model analysed using the ESS approach. The model includes resource allocations to male and female reproductive structures at the time of flowering and to fruit maturation. The formulation allows for non-linear relations between opportunities for fertility gain on the one hand and flower and fruit size and number on the other. Results of the model indicate that fewer fruits will be matured than flowers produced, even in the absence of previously suggested factors such as pollinator limitation and bet-hedging in the face of environmental variability. Model results emphasize the distinction between flower versus inflorescence contributions to male and female reproductive success. Analysis also shows that the fruit to flower ratio in hermaphroditic plants will be lower than that in female plants, in accord with broad taxonomic surveys. Finally, results obtained lead to empirically testable predictions about the relationship between flower size, fruit size and the fruit to flower ratio. Methods to test these predictions are discussed.