PARENT SESSION
Oral Session #30: Landscape Ecology: Dynamics and patterns. Presiding: A. Hansen.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Madison Ballroom D.
Modeling the population-level mechanics of species range stability.
Nesslage, Genevieve1, Skillen, Jennifer1, Kahl, Katherine1, Maurer, Brian1, Taper, Mark2, 1 2
ABSTRACT- At the geographic scale, species exhibit a positive relationship between mean population abundance (x) and population variance (s2) over time as described empirically by Taylor's power law (s=axb). The exponent, b, is an important indicator of species range stability. Range stability increases (or decreases) as b decreases (or increases). To identify the mechanisms underlying Taylor's power law, we modeled growth in 20 hypothetical populations of Red-eyed Vireo (Vireo olivaceus) using the stochastic Ricker growth equation. Initial population parameters included rate of growth, a density dependent factor, and stochastic environmental variation. We parameterized our model by randomly selecting values from within a uniformly distributed range identified from Breeding Bird Survey data. The mean and standard deviation of abundance for each population modeled over 5000 time steps were used to estimate b. The model was run 100 times, resulting in a range of b values for the Vireo from 1.3-1.4 that were reasonably close to the empirical estimate of 1.3. A graph of parameter space indicated that our 20 samples were randomly distributed with many low abundance populations and only a few high abundance populations. This pattern corresponds well with the hollow curve distribution associated with population surveys. Our model may be used to better understand the population-level dynamics that contribute to Taylor¿s power law and observed patterns in species range expansion or collapse.
KEY WORDS: Taylor's power law, geographic range stability, Vireo olivaceus