. Bison with nursing calf. The next step in the analysis was to construct a simple deterministic (averaging) population model that included estimates of the rate of change in the population, taking management actions into account, and estimates of changing seroprevalence rate. The rate of increase was calculated using the rate of change between the late winter population, after management removals and natural mortality, and the fall high population count for the following year (Eberhardt 1987). Early winter bison population counts and removals (Meagher, unpub. data; National Park Service and S
. Bison with nursing calf. The next step in the analysis was to construct a simple deterministic (averaging) population model that included estimates of the rate of change in the population, taking management actions into account, and estimates of changing seroprevalence rate. The rate of increase was calculated using the rate of change between the late winter population, after management removals and natural mortality, and the fall high population count for the following year (Eberhardt 1987). Early winter bison population counts and removals (Meagher, unpub. data; National Park Service and State of Montana 1996; National Park Service, unpub. data) from 1979 to 1997, when the population ranged between 1,700 and 3,500 animals, were used to calculate the rate of change for the bison population (see table 29). The geometric mean of the rate of change was calculated to be (see table 29); this means the bison population increased at an average rate of over (his time period. This rate was validated using actual population counts through 1996. Based on management removals from 1984-85 to 1995-96, an average of % of the total early winter bison population exited Yellowstone National Park into the Reese Creek area north of the park and the West Yellowstone area west of the park (see table 29). The value was used in the model to calculate the average total number of bison exiting the park each year. Past data indicate that after large removals in the Reese Creek area, few bison exit the north boundary area for approximately two years. This trend is expected to continue, and very few or no bison are expected to exit to the north boundary area prior to 1999. Based on the large number of bison removed from the Reese Creek area in the winter of 1996-97, the model assumed no bison would exit the Reese Creek area until 1999. Bison were assumed to exit the park during winter at the West Yellowstone area for all years in the model. Comparing total removals a
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