Abstract
Long-term data on population dynamics from 20 study sites including 15 species are reviewed. Data include both continuous and discrete changes, or data cover only a few group(s) or the entire population. Median of the ratio of the maximum population size to minimum population size during the entire study period was 2.12. Median of the largest annual decrease observed in each study site was 22%, and it was significantly larger than the largest annual increase, suggesting that decrease is faster than increase of population size. The frequency of events that population size decreases 10% or 20% was every 6.15 and 20 years, respectively. If data which cover the entire population are included, the frequency was 4.5 and 10.3 years, respectively. Although data on the continuous changes in population size of more than 20 years are available for only four study sites so far, this empirical evidence and the above parameters suggest that fluctuation is the normal state for primate populations, and they hardly reach equilibrium.
