Life Histories of Mammals: An Analysis of Life Tables

We quantitatively test theoretical predictions concerning mammalian life histories, using published data on survival, reproduction, and body mass for 29 eutherian mammals. Larger mammals have a greater age at maturity, greater generation length, greater life expectancy, lower reproductive value at maturity, and smaller litters than do smaller mammals. Residual reproductive value at maturity is not correlated with adult body mass or survival. Litter size varies inversely with generation length and adult survival. Age at maturity is positively correlated with life expectancy. Twenty—seven of 29 mammals display a generation length longer than their life expectancy at birth, and the same proportion shows a greater life expectancy at maturity than at birth. A fairly high proportion (76—82%) of the variation in these dependent variables is attributable to adult mass. Many life table characteristics of mammals are interrelated, although not necessarily in the ways predicted by theory. Design constraints may preclude significant differences in life history patterns among mammals, so that the life table characteristics of only a few species may depict the pattern of life table evolution in most eutherian mammals.