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 d ata 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 lif e-tables that assumes animals are at risk for the entire age-class. This st udy concludes that prorating risk may invalidate population growth projecti ons by significantly and unequally over-estimating fecundity and mortality rates. This effect is most pronounced in species that have distinct breedin g seasons (birth pulse populations), seasonal mortality, and small data set s. Recommendations include using a non-prorated methodology, tabulating lif e-tables using only completely known age-class data, and combining populati on parameters for emigrations, releases, and deaths for population growth p rojections. Zoo Biol 20:279-291, 2001. (C) 2001 Wiley-Liss, Inc.