POPULATION PERSISTENCE TIME - ESTIMATES, MODELS, AND MECHANISMS

The conservation and management of populations require some insight in to mechanisms of population regulation, yet unambiguous identification of density dependence in vital rates is notoriously difficult. Throug h the reanalysis of data published by Stacey and Taper for a semi-isol ated sub-population of the Acorn Woodpecker we demonstrate the utility of an approach in which a single data set is ''attacked'' using a sui te of models with different assumptions. Tests for density dependence of the reproductive rate and of juvenile survival are inconclusive, bu t there is evidence for density-dependent adult survival. Since ''surv ival'' rates estimated from banded birds confound the effects of morta lity and immigration/emigration, we construct and analyze three models : (1) a closed population with density-independent vital rates and an upper limit to population size, (2) a regulated closed population, (3) a regulated sub-population with immigration and emigration. Very smal l interchanges with other sub-populations can have a very large effect on population persistence; thus our results highlight the importance of distinguishing the effects of interchange from density dependencies in vital rates.