Seed size optimization in a wind dispersed tree Butea monosperma: a trade-off between seedling establishment and pod dispersal efficiency

Abstract

Seed size optimization theories are generally based on the assumption that seedling fitness increases at a decreasing rate with seed size. But often, offspring fitness is also influenced by other components such as dispersal efficiency, especially in wind, water and animal dispersed species. We argue that in these species where the dispersal efficiency of the seeds and fruits decreases with the seed mass, the latter is optimised in order to maximize the product of the two components of offspring fitness namely, seedling establishment and dispersal efficiency. In this paper, we show that seed mass in a wind dispersed tree, Butea monosperma is a consequence of selection in opposite directions to favour seedling establishment on one hand and wing loading (dispersal efficiency of pods) on the other hand. We also discuss the interaction of various components of the pod in optimising the seed size.