Population Dynamics

One of our persistent questions since the beginning of the project has been, how stable is the baboon population in Amboseli? In the 1960's, the population experienced a dramatic crash, from which it slowly recovered over the next two decades, although it never regained its former numbers [64, 108]. In 2000, we constructed a demographic model of the Amboseli baboon population that suggested that since the early 1970's the population has been growing at a robust 4% per year. However, that model did not take into consideration year-to-year fluctuations in growth rate due to changes in predation and food availability - it simply pooled all birth rates and death rates since 1971 into a single value for each age group.

We know that fluctuations in birth and death rates have occurred, however, partly because the baboon groups have all shifted their home ranges at some point in the past decades. Such shifts usually result in an increase in both food and predation. Our current work involves investigating the effects of such fluctuations on the population growth rate. Analyses so far suggest that these fluctuations are very dramatic, so that while the pooled population growth rate has been 4% per year, growth rates over smaller periods of time, looking at single groups, may be as high as 8% per year and as low as -4% per year - from high growth to actual shrinkage. The implication of these fluctuations is that, while the baboon population may continue to grow if it remains on its current trajectory, it may also shrink and become vulnerable to extinction. Several bad years in a row, for instance, would accumulate in such a way that another crash could easily occur. We are currently in the process of trying to measure the possibilities - will the population continue to expand, or will it crash and return again to the edge of local extinction?