Life history strategies

Just like gamete production, offspring production can follow the same two strategies: quantity or quality. The quality strategy is best exemplified in African elephants (Loxodonta africana), the largest living land animal. African elephants produce one young, rarely two, after a gestation of 22 months. Young are born precocial, and can stand up and follow the mother within 15-30 minutes. They are nursed for 2-3 years (sometimes up to 9 years), and reach sexual maturity at 8-13 years of age. In their lifetime of 55-60 years, female elephants average four calves, with a range of one to nine.

In contrast to the "quality" strategy of elephants, numerous rodents and lagomorphs have multiple litters each year, each with numerous young, and spend little time investing in

An African elephant (Loxodonta africana) bull in "musth," a state of sexual excitement characterized by aggressive posturing, continuous dribbling of urine, and secretions running from the temporal glands. (Photo by Rudi van Aarde. Reproduced by permission.)

offspring growth (quantity strategy). Obviously, a continuum exists between the two extremes and typically these life history strategies are influenced by the size and life span of the animal and the environment. For example, small rodents grow faster, and live shorter lives, and thus invest in "faster" reproduction such as earlier age at maturity, and smaller but more numerous neonates. In contrast, larger mammals such as ungulates, elephants, and whales have relatively larger but fewer neonates, and attain sexual maturity much later. The latter species are typically longer-lived, and thus spread their reproductive efforts over a longer time span than smaller mammals.

0 0

Post a comment