Natural Selection of Wild Reindeer Life History Traits by Food Limitation and Predation

Fecundity, age-size at maturity, reproductive effort and mortality of two Norwegian wild reindeer herds were compared with two Canadian wild caribou herds. Wild reindeer mature earlier, and under food stress maintain maturity at lower body size. The allocation of resources to early reproduction under food stress halts reindeer body growth at half the mature body size of caribou which mature at a later age. Directional selection against the largest adult wild reindeer phenotypes by human hunters has lowered the mean body weight of adult females, yearlings and calves. Under food stress normalizing selection against the smallest neonates by starvation was not able to counteract the effects of food limitation on growth after maturity or the effects of directional selection on large phenotypes by predation. Adult sizespecific predation on reindeer by modern man and juvenile predation on caribou by wolves have resulted in widely different juvenile to adult survival ratios between reindeer and caribou. This variation may be responsible for the observed differences in maturity and reproductive effort between reindeer and caribou.