Document: MEG-3-51-31

Is scale transition theory a useful tool for understanding spatial dynamics?

DONAHUE, M.J.* and M.HOLYOAK

University of California, Davis, CA 95616 USA ¹

Abstract:
Scale transition theory predicts changes in population dynamics across spatial scale due to the interaction between local density dependence and variation in population density across patches. This transition enhances regional stability by making regional dynamics less temporally variable than local dynamics. Stronger scale transitions are expected with patchy resource distributions or low rates of between-population dispersal. We tested how dispersal, resource distribution, and density dependence affect scale transitions in single-species microcosms. Our study spanned at least 150 generations. Microcosms consisted of four bottles connected by tubes to create different dispersal levels. All microcosms had equal amounts of total resources but varied in resource distribution. The amount of density dependence was manipulated by using three species. Perturbation experiments, together with fitting of logistic models, showed 10-fold differences in the strength of density dependence (the second derivative of the logistic equation, r/K) among these species. The species with the least density dependence showed significantly more temporal variability in regional dynamics than the other two species. For Colpidium, low-dispersal microcosms showed lower temporal variability in regional dynamics than microcosms with high or no dispersal. Non-linear time series techniques were used to fit a logistic model to each patch. The mean of the patch models was then used to predict the microcosm dynamics. The difference between predicted and observed dynamics within entire microcosms was used as a measure of the extent of the scale transition. Results supported the prediction of scale transition theory: Larger differences occurred in microcosms with the lowest dispersal, highest resource variability, or the species with the strongest density dependence. Our study shows that scale-transition theory is a useful tool for synthesizing ideas about spatial dynamics.

Keywords: density dependence, metapopulation, microcosm, protist, source-sink, scale transition, spatial scale

This abstract is being presented at: 4:45 PM in session:
Oral Session #11: Trophic Cascades.