Mortality Patterns in Mammals

TLDR

Methods for obtaining life‑table data are outlined, noting that most approaches assume a stationary distribution and that existing tests of stationarity are invalid. The study constructs bias‑adjusted life‑table and fecundity tables for *Hemitragus jemlahicus* and compares its mortality‑rate curve with those of other mammals, revealing common characteristics across species. The analysis estimates a mean generation length of 5.4 yr, an annual mortality rate of 0.25, and a life expectancy of 3.5 yr, supporting the hypothesis that mammalian life tables share a common form and that age‑specific mortality patterns are approximately constant across species.

Abstract

Methods of obtaining life table data are outlined and the assumptions implicit in such treatment are defined. Most treatments assume a stationary are distribution, but published methods of testing the stationary nature of a single distribution are invalid. Samples from natural populations tend to be biased in the yound age classes and therefore, because it is least affected by bias, the mortality rate curve (q x ) is the most efficient life table series for comparing the pattern of mortality with age in different populations. A life table and fecundity table are presented for females of the ungulate Hemitragus jemlahicus, based on a population sample that was first tested for bias. They give estimates of mean generation length as 5.4 yr, annual mortality rate as 0.25, and mean life expectancy at birth as 3.5 yr. The life table for Hemitragus is compared with those of Ovis aries, O. dalli, man, Rattus norvegicus, Micortus agrestis, and M. orcadensis to show that despite taxonomic and ecological differences the life table have common characteristics. This suggests the hypotheses that most mammalian species have life tables of a common form, and that the pattern of age—specific mortality within species assumes an approximately constant form irrespective of the proximate causes of mortality.