The mortality data was collected physically in the form of a historic cohort where individuals who died before 1900 were recorded. The total number of the population sample is two hundred and thirty individuals with dates of births ranging from 1750 to 1899. With this information a life table for the historic cohort and a survivorship curve will be determined and assessed to determine its significance to Molles assertion. .
As mentioned above, there are three types of survivorship curves. A type I curve indicates that most individuals die in a post-reproductive stage, juvenile survival is high and most mortality occurs among older individuals. A type II curve indicates that a mortality rate is constant over the individuals lifespan. A type III curve indicates most individuals die early in life (French, 1996). Based on the collected mortality data the survivorship graphed in Figure 1 (see attached) resembles a type I survivorship curve. This result supports Molles' claim that human survivorship follows a type I survivorship curve. In general the survivorship curve displays a relatively shallow, linear gradual slope until about the age interval of 70 to 79 where the slope begins to decrease significantly. Survivorship is relatively high for the first twenty years and gradually declines until about age 80. After age 80 the survivorship rapidly declines in the older individuals. .
The survivorship curve also shows that the mortality rate is not constant which indicates that individuals experience differences in their life stages. Life stages (or life history) describes the ecological or environmental and evolutionary parameters that influence survivorship curves. These factors inlcude biotic/abiotic factors and genetic predispositions. The assumption in static life tables however suggests that all individuals sampled are exposed to the same environmental conditions. In the above sample there were no records of immigration simply because of the lack of authentic evidence and support.
Survivorship curves are data from column lx in a life table plotted on semilog paper. For wildlife managers using there tables and curves is very useful in populations. ... The survivorship curve is used to see how long the species lives before it starts to decline of old age and eventually die. 4. ...