Body Size, Breeding Season Length, and Life History Tactics of Lagomorphs

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Abstract
Patterns of reproduction were investigated for 22 spp. of lagomorphs (rabbits, hares, pikas). Neonatal body mass, gestation time and maternal reproductive effort during gestation scaled allometrically with body mass of adult females. In keeping with their relatively altricial state at birth, Sylvilagus (Gray) exhibited shorter gestation periods and lighter neonatal body masses than comparable size-independent values for Lepus (L.). Much of the variation in reproductive characteristics of lagomorphs was exlained by body size and phylogeny. Analysis by principal componentsrevealed reproductive parameters that were largely independent of body size. Examination of these 2nd-order strategies showed that lagomorphs differ regarding rates of development and the manner in which offspring are produced (i.e., litter size, maternal investment). Breeding season length is a primary determinant of this differentiation. Selection has favored a reproductive strategy in highly seasonal environments characterized by fewer, larger litters; long breeding seasons permit increased productivity via reduced age at 1st reproduction and increased iteroparity. The mean fetal growth rate of lagomorphs was more rapid than rates of other orders of eutherian mammals, but maternal reproductive investment during gestation was similar among orders.