JSM 2005 - Toronto

Abstract #302803

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Legend: = Applied Session, = Theme Session, = Presenter
Activity Number: 465
Type: Invited
Date/Time: Thursday, August 11, 2005 : 8:30 AM to 10:20 AM
Sponsor: Biometrics Section
Abstract - #302803
Title: Spatial and Temporal Variability Exert Opposing Effects on Density Dependence in Populations of Large Herbivores
Author(s): Guiming Wang*+ and Tom Hobbs and Randall B. Boone and Andrew W. Illius and Iain J. Gordon and John E. Gross and Kenneth L. Hamlin
Companies: Colorado State University and Colorado State University and Colorado State University and University of Edinburgh and CSIRO and National Park Service and Montana Fish, Wildlife, and Parks
Address: Natural Resource Ecology Laboratory, Fort Collins, CO, 80523,
Keywords: Bayesian hierarchical model ; climate variability ; density dependence ; large herbivores ; Markov Chain Monte Carlo Method ; normalized difference vegetation index
Abstract:

A central challenge in ecology focuses on understanding the interplay of internal and external controls on the growth of populations. We examined the effects of temporal variation in weather and spatial variation in vegetation on the strength of density dependence in populations of large herbivores. We fit three subsets of the model to five time series of estimates (Nt) of abundance of ungulates in the Rocky Mountains. The strength of density dependence was estimated by the magnitude of the coefficient b. We regressed the estimates of b on indices of temporal heterogeneity in weather and spatial heterogeneity in resources. The 95% posterior intervals of the slopes of these regressions showed temporal heterogeneity increased the strength of density-dependent feedback to population growth, while spatial heterogeneity weakened it. This finding offers the first empirical evidence that effects of spatial heterogeneity on density dependence oppose the effects of temporal heterogeneity. The results imply fragmenting habitats might cause reductions in herbivore abundance, even when total resources remain constant.

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