Packaging and provisioning in plant reproduction

Abstract

Plant reproductive ecologists investigate many aspects of reproductive design not covered by simple offspring size/number models or simple sex allocation models, such as inflorescence design, pollen packaging or fruit design. General models for hierarchical packaging of reproductive allocation which cover these and other cases are developed here. These demonstrate that selection will tend to equalize fitness elasticities of reproductive components when these are properly scaled to take account of reproductive costs. Elasticities are defined as the proportional change in a fitness component with a proportional change in the trait contributing to that component (e.g. the proportional change in the fitness per seed with a proportional change in seed size). For the simplest reproductive design models, selection will favour the equalization of the elasticities of all female hierarchical provisioning and packaging fitness components or all male packaging components, both in single sex models or cosexual models. For simple cosexual models, selection favours allocation to each sex in proportion to the genderspecific fitness elasticities. More generally, selection tends to equalize all component elasticities when these are properly scaled to account for the total resource costs of changes in each component. The models are extended to cover more complex biology, including links between female and male packaging components, packaging components that contribute to the fitness of both genders, accessory costs that may or may not contribute to both genders, and allometric costs and trade-offs. As assumptions about fitness interactions and life history trade-offs become less restrictive, the models more closely approach a general equal-marginal-advantage model. The models provide tools for understanding how and when different components of the reproductive design constrain and selectively impact each other. The utility of the model for aiding in the design and analysis of specific research problems is discussed with reference to some empirical examples.