POPULATION VIABILITY ESTIMATES - THEORY AND PRACTICE FOR A WILD GORILLA POPULATION

The logic of demographic modeling, the apparent simplicity of its quan tifiably, substantiated answers and the ready availability of software correlate with increasing use of demographic modeling as the means of applying biology to the conservation of potentially endangered popula tions. I investigated that use by considering a small population (abou t 300 individuals) of a large forest-dwelling mammal of the tropics, t he Virunga gorilla (Gorilla gorilla) of Zaire: Uganda, and Rwanda Beca use censuses of forest populations are so inaccurate and data on varia nce of some parameters takes so long to collect models might not be br oadly applicable. Therefore simple demographic indices of potential ex tinction should replace sophisticated models The current best index co uld be problematic however, because it is based on detecting adult mor tality, perhaps the most difficult demographic parameter to measure. M odels of the Virunga gorilla population that incorporate aspects of de mographic heterogeneity valuably indicate genetic and demographic pers istence for several hundred years. Deterministic change in habitat is a greater threat than stochastic demographic variation and yet our eco logical ignorance is such that we could not begin to model the consequ ences of removal of even the main food plant We must add to our abilit y to model outcomes of demographic perturbation a far greater understa nding of the processes by which the perturbations occur. Demography al lows res to model demographic response to demographic change, but we u sually, need ecology to tell us how the threat produced the demographi c change in the first place. In a time of change accurate prediction r equires ecological understanding of process as well as demographic und erstanding of outcome.