The effects of prorating risk in the development of life‐tables

This study used computer models to investigate two different strategies for assessing risk in the development of age-based life-tables from studbook data sets. One methodology is similar to that currently employed in American Zoo and Aquarium Association population management, which prorates animals at risk within age-classes. The other follows the method used in human life-tables that assumes animals are at risk for the entire age-class. This study concludes that prorating risk may invalidate population growth projections by significantly and unequally over-estimating fecundity and mortality rates. This effect is most pronounced in species that have distinct breeding seasons (birth pulse populations), seasonal mortality, and small data sets. Recommendations include using a non-prorated methodology, tabulating life-tables using only completely known age-class data, and combining population parameters for emigrations, releases, and deaths for population growth projections. Zoo Biol 20:279–291, 2001. © 2001 Wiley-Liss, Inc.