ELK POPULATION PROCESSES IN YELLOWSTONE-NATIONAL-PARK UNDER THE POLICY OF NATURAL REGULATION

The interrelations of weather, plant production and abundance, and elk population dynamics on Yellowstone's northern winter range were exami ned for a 23-yr period when there was minimal human offtake from the h erd. Significant correlations between precipitation and plant producti on, between elk population responses and precipitation, and between el k population responses and elk population density strongly suggested t hat forage limited elk population growth. Although population response s to density have been documented previously in Yellowstone, responses to precipitation have not. Correlations between elk population respon ses and annual precipitation were presumably consequences of plant gro wth responses to precipitation and subsequent effects on elk nutrition al status. Population regulation was most consistently achieved throug h the responses of juveniles rather than adults. Winter mortality of j uveniles was primarily correlated with elk numbers, whereas recruitmen t was primarily correlated with precipitation. Adult mortality rates w ere not significantly correlated with elk numbers, but were correlated with precipitation. Per capita rate of increase was negatively correl ated with elk number, but 55% of the variance was density-independent. There was evidence that winter weather affected the elk, but season-l ong weather indices had poor predictive power. A stage-structured popu lation model using regression equations of mortality and recruitment r ate responses to precipitation and elk numbers, predicted that the pop ulation could vary within a range of approximate to 16 400 +/- 2500 si ghted elk (mean +/- 1 SD).