Natural Selection of Optimal Reproductive Tactics

Abstract

Acting through differential reproductive success, natural selection has produced a great diversity of existing reproductive tactics, each of which presumably corresponds to a local optimum that maximizes an individual organism's lifetime reproductive success in its particular environment. A body of theory on so-called reproductive “strategies” has yet to be adequately related to an independent theoretical framework on optimal foraging tactics. Some of the possible interactions and constraints between an animal's input of matter and energy via foraging and its output in offspring using these same materials are briefly considered. For example, storage and utilization of lipids allow an organism to gather and sequester matter and energy during a period that is not suitable for successful reproduction, but enable the organism to expend those materials at a later, more satisfactory time. Such interactions between foraging and reproduction lead to a sort of temporal integration, which greatly complicates estimation of reproductive effort (current investment in seed, eggs, or progeny) in variable environments. An optimal reproductive tactic maximizes an individual's reproductive value (the sum of all present plus the expected probable number of all future offspring) at every age. Reproductive effort should vary inversely with residual reproductive value (expectation of future offspring); moreover, the precise form of the trade-off between present offspring versus future progeny, which is itself sensitive to a multitude of environmental influences including resource availability and the immediate environmental conditions for reproduction and survival, dictates the optimal tactic at any given age. Simple graphical models of optimal reproductive tactics are presented and discussed. Finally, some promising directions for future work, as well as certain potential difficulties, are noted.