PARENT SESSION
Oral Session #90: Evolutionary Ecology.
Presiding: R. del Castillo
Thursday, August 8. 1:00 PM to 3:45 PM. Apache Meeting Room, TCC.
Intraspecific character displacement and sexual dimorphism in habitat utilization.
Jerde, Christopher*,1, Taper, Mark1, Meagher, Mary1, 1 Montana State University, Bozeman, Montana
ABSTRACT- From 1970 to 1997, 151 flights were taken in a fixed wing aircraft to collect data on numbers, habitat locations, and demographics of Yellowstone National Park bison. Previous analysis on this data demonstrates the bison's social drive to aggregate. One noticeable characteristic was the segregation of mature bull groups away from the large cow, calf, and sub-adult male mixed aggregations during non-rutting periods. Many large ungulate species demonstrate sexually dimorphic characteristics while maintaining large demographically mixed groups. The sexual dimorphism is usually attributed to competition for mates or protection of young. Using historical data on sex and body size, analysis suggests sub-adult males are approximately the same weight as a mature cows and mature bulls are on average 1.6 times larger. This study uses bootstrapped, loess smoothing techniques to demonstrate the significant difference in habitat utilizations between adult bull bison and cow, calf, and sub-adult bull mixed groups. Prior research into mammal metabolism implies that large mammals use higher quantities of lower quality forage as compared to smaller mammals that require lower quantities of higher quality forage. The hypothesis of sexual dimorphism as a potential mechanism to intraspecific character displacement is presented.
KEY WORDS: Sexual Dimorphism, Habitat Utilization, Character Displacement, Bison