| ABSTRACT
We examined two factors that directly affect population growth of American bison (Bison bison) on Antelope Island State Park, Utah. First, we studied patterns of social organization during times of sexual segregation and aggregation. We discovered that sexual segregation is driven primarily by ecological factors as opposed to social phenomenon .
Males resided in areas characterized by high human activity and vegetative degradation. Females were located far from human activity, especially during parturition (birthing season) when females used high-elevation terrain. Social segregation hypotheses cannot explain
those long-term differences in space-use between males and females.The predation hypothesis, a prominent hypothesis under ecological segregation, can explain that difference in space use throughout the study. Furthermore, factors from the gastrocentric hypothesis were evident because females frequently utilized areas of high forage quality, in particular high elevations and fields seeded with alfalfa mixtures. Understanding where and why females use habitat can greatly influence choices regarding habitat manipulation.
Second, we constructed a comprehensive index to forage productivity and examined changes in vegetative growth over time. Variables on local weather (average temperature and total precipitation), and vegetative growth (percent change in NDVI, and tree-ring width) were combined in a pri ncipal components analysis (PCA). Using the PCA, we clustered
years into high and low vegetation productivity. Although we detected an increase in temperature, there was no corresponding change in growth of trees or total annual precipitation since 1950. Knowledge of short- and long-term patterns of vegetative productivity are critical for understanding variation in population growth of ungulates. |