Growth, reproduction and resource allocation in the Norwegian lemming Lemmus lemmus (L.) under controlled conditions

Lemmings from a laboratory colony did not show statistically significant differences in growth between the sexes up to an age of 50 days. After this, growth slowed down, but adult individuals continued to gain weight, some reaching more than 100 g. Reproductive females gained more weight than non-reproductive. Maximal longevity was between 2 and 3 years. The Norwegian lemming has high reproductive potentials. Females became sexually mature at about 3 weeks of age, even down to two weeks, and remained sexually active until the last periods of life. With 8 mammae and an average litter size of 4, our material confirmed the one-half rule. Litter size up to 16 was recorded. With post-partum oestrus, litters were born at 21 day intervals. Pregnancy and lactation therefore overlapped. Resource allocation between the mother’s demands and those of the two sets of progeny, is achieved partly because the lactation period is so much shorter than the gestation period. Thus competition for energy is reduced. We did not observe any negative effects of the presence of sucklings on the ensuing litter. Even with concurrency in pregnancy and lactation the female herself gained some weight. The Norwegian lemming is thus capable of rapid population growth.