EFFECTS OF PARENTAL SURVIVAL ON CLUTCH SIZE DECISIONS IN FLUCTUATING ENVIRONMENTS

Whereas in constant environments parental survival has no effect on op timal clutch size in the absence of trade-offs between juvenile and pa rental survival, the situation is drastically different in fluctuating environments. We consider a model in which, with respect to reproduct ion, parents and offspring are equivalent at the start of the next bre eding season. When generations are non-overlapping, the clutch size ma ximizing geometric mean surviving number of offspring is optimal among all pure clutch size strategies. We prove that, as parental survival increases relative to that of the offspring, the optimal clutch size c onverges to the arithmetic mean maximizing clutch size (the so-called `Lack clutch size'). We also give a numerical procedure for calculatin g optimal mixed strategies and we show that, as environmental variance increases and/or parental survival decreases, mixed rather than pure strategies become optimal. Furthermore, we explain how to estimate fit ness from empirical data under the assumptions of our model.