PARENT SESSION
Oral Session #48: Spatial patterns, spatial processes. Presiding: D. Deutschman.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Madison Ballroom C.
The phenology of space: Spatial density dependence in Yellowstone National Park bison.
TAPER, MARK1, MEAGHER, MARY1, JERDE, CHRISTOPHER1, 1
ABSTRACT- From 1970 to 1997, 151 flights were taken in a fixed wing aircraft to collect data on numbers, locations, and group structure of Yellowstone National Park (YNP) bison. This population represents the only continuously wild and free ranging bison in the United States. Bison population numbers show a remarkably steady increase until the very end of this period. Density dependence is difficult to establish because the bison use of space in YNP shows pronounced seasonal variation. Areas used were estimated for all flights by kernel density range analysis. Population densities for each flight are calculated using these areas. Competition is most severe in winter. We detect a significant relationship between minimum winter population density and yearly growth rate. The YNP bison can be divided into northern and central herds. Only modest exchanges occur between them. The spatial dynamics of the central herd undergoes a marked change around 1982. Until this time, as the population size increased so did population density. After 1982, population density remains constant as both population size and range increases. The primary expression of density dependence in YNP bison is range expansion.
KEY WORDS: density dependence, yellowstone, bison, Bison bison