Browsing by Author "Priddy, J. A."
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- Population viability analysis for red-cockaded woodpeckers using an individual-based modelWalters, J. R.; Crowder, L. B.; Priddy, J. A. (Ecological Society of America, 2002-02)Red-cockaded Woodpeckers (Picoides borealis) are distributed in the southeastern United States among closed populations whose maximum size is limited. Previous population viability analyses for this species have been confined to examination of threats posed by catastrophes and loss of genetic variability, because of the lack of demographic models that incorporate the extreme spatial constraints on dispersal that characterize this species. We used a spatially explicit, individual-based simulation model to assess the vulnerability of Red-cockaded Woodpecker populations to demographic and environmental stochasticity. Vulnerability to these threats was relatively low, because the presence of a substantial nonbreeding class (i.e., helpers) ameliorated the impact of stochastic variation in mortality and reproduction on the size of the breeding population. Because dispersal of helpers is spatially restricted, this effect was most pronounced when territories were aggregated or at high densities. Populations of 250 and 500 territories were stable regardless of the level of territory aggregation at the densities examined, whereas populations of 25, 49, and 100 territories ranged from rapidly declining to stable, depending on territory density and level of aggregation. Techniques that enable managers to maintain existing territories and create new ones are well established for this species. Thus managers may reasonably expect to maintain even small populations of Red-cockaded Woodpeckers by increasing the density, level of aggregation, and number of territories.
- Testing a spatially explicit, individual-based model of red-cockaded woodpecker population dynamicsSchiegg, K.; Walters, J. R.; Priddy, J. A. (Ecological Society of America, 2005-10)Stochastic population models are widely used to assess extinction risk under various management scenarios, but due to the lack of independent data, such models are tested only rarely. Here we evaluate the predictive accuracy of a stochastic, spatially explicit, individual-based model of the population dynamics of the Red-cockaded Woodpecker by comparing simulated data with independent empirical data sets from two populations. We examined primary model predictions such as Population size and number of territories, and secondary predictions such as population structure, dispersal success, natal dispersal distances, and age distributions. The model predicted most evaluated parameters with high accuracy, but model performance could be enhanced by including pioneering behavior and by improving estimates of mate and female dispersal behavior. We judge our model to provide reliable predictions when applied to real populations, with a few specific exceptions.