Date of Award:
Doctor of Philosophy (PhD)
Department name when degree awarded
Robert J. Taylor
Gregarious behavior of ungulates was considered in four ways. The first concern was W. D. Hamilton's hypothesis that a simple movement rule could reduce predation risk and encourage grouping behavior. Simulations showed little effect of this nearest-neighbor rule on predation risk. Similar, more complicated rules reduced predation risk by up to two thirds.
The second focus was on the accuracy of ground observers in diagramming individual animal locations in small herds of elk. A remotely controlled airplane was used to photograph the herds from above. A substantial distance discrepancy was found between "true" and "observed" animal locations. This discrepancy increased with group size and was different between observers but not between herds. Observers were better at predicting relative animal locations than absolute animal locations.
The third consideration was interanimal spacing in bison herds photographed from an airplane during a three-month period. At later dates photographed herds were located, and cover-sampling methods were adapted to estimate bison visibility in each area. These data were used in linear regression models which explained over two-thirds of the variance in nearest-neighbor distance. Important indicator variables were the number of animals in the herd, a cover measurement, the north and east location of herds, the time photographed, and the fraction of the animals standing.
The fourth focus was the development of simulations of simple movement rules used to mimic grouping behavior. Individuals moved according to two simple first nearest-neighbor rules: if within a minimum distance, move directly away, and if outside a maximum distance, move directly toward. Four other rules were used to determine individual states. Two different measurements were made for each simulation run: the overall mean nearest-neighbor distance and the overall mean subgroup size. Results showed that the means and variances of near-neighbor distances decreased as the number of individuals in the simulation increased. Different near-neighbor rules had little effect on mean nearest neighbor distance. All rules produced results similar to each other and different from bison data. A random model was more similar to the bison data.
Morton, Thomas L., "Gregarious Behavior in Large Mammals: Modeling, Methodology, and Application" (1993). All Graduate Theses and Dissertations. 6489.
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