Is there an Optimal Clutch Size in Snow Geese?

We examined the relationship between clutch size and total fitness in the lesser snow goose (Anser caerulescens) employed a life-cycle model in which successive life stages are used to estimate fitness components. Though there are trade-offs involving some components of fecundity, the effects are not sufficient to offset initial differences in clutch size. Further, there is no evidence that viability depends on reproductive performance. Overall, there is a positive relationship between clutch size and total fitness consistent with directional selection favoring larger clutches. This contrasts with many theories of clutch-size evolution, which predict a relationship more consistent with stabilizing selection. The pattern of directional selection raises the twin questions of why the mean clutch size of the population is smaller than the most productive clutch size, and why there is variation about that mean. We offer three resolutions that incorporate the influence of a recent shift in the selection regime, gene flow, spatiotemporal variation in nutrients, and cultural transmission of behaviors associated with feeding.