Clutch size, offspring performance, and intergenerational fitness

It is now generally recognized that clutch size affects more than offspring number. In particular, clutch size affects a suite of traits associated with offspring reproductive performance. Optimal clutch size is therefore determined not by the numerically most productive clutch but by the clutch that maximizes collective offspring reproductive success. Calculation of optimal clutch size thus requires a consideration of ecological factors operating during an intergenerational time frame, spanning the lifetime of the egg-laying adult and the lifetimes of her offspring. The optimal clutch cannot define reproductive values in advance, but instead requires that the strategy chosen is the best response to the set of reproductive values that it itself generates. In this article, we introduce methods for solving this problem, based on an iterative solution of the equation characterizing expected lifetime reproductive success. We begin by considering a semelparous organism, in which case lifetime reproductive success is a function only of the state of the organism. For an iteroparous organism, lifetime reproductive success depends upon both state and time, so that our methods extend the usual stochastic dynamic programming approach to the evaluation of lifetime reproductive success. The methods are intuitive and easily used. We consider both semelparous and iterparous organisms, stable and varying environments, and describe how our methods can be employed empirically.