Births, deaths, immigration, and emigration cause population dynamics, and are referred to as demographic events. Life tables are a tool used to summarize patterns of births and deaths. It also often shows the number of offspring they produced during each time interval. Most life tables are constructed only for females because the production of offspring by males is hard to estimate.
Ecologists also use graphs called survivorship curves to show the relationship of age to survival.
In Type I survivorship curves, nearly all individuals survive for their entire potential life span and then die almost simultaneously. In Type II curves, survival is the same across the life span. In Type III curves, survival of young individuals is low, but survival is high across the remainder of the life span. Survivorship data from real populations often resembles one of these hypothetical survivorship curves. Growth of populations is also described using mathematical functions.