UBC Theses and Dissertations
Investigation of causes of the 10-year hare cycle Trostel, Kendrick A.
This thesis combined data from a trapping and radio-telemetry study of snowshoe hares at Kluane Lake, Yukon from January 1984 through August 1985 with data collected at the same site from 1977-83 (Boutin et al. 1986; Krebs et al. 1986) to examine possible causes for the 10-year cycle in density of snowshoe hares. In Chapter 2 I used data on causes of mortality, from a radio-telemetry study of a cyclic snowshoe hare population during 1978-84, to consider the importance of predation in causing the hare cycle. I found that predation during winter was the largest source of mortality for snowshoe hares during 1978-84. There was a 1-year lag in the response of predation mortality to changing hare density. There was a 2-year lag in the response to changing density of mortality due to causes other than predation. I incorporated this information on causes of mortality into a simulation model, to see whether observed predation mortality can cause changes in density similar to those of a cyclic population. I fitted the predation mortality data to a function in which total predator response consists of a Type II functional response and a delayed density-dependent numerical response. Using a simulation model that predicted mortality rates with this function, I produced 8-11 year cycles within parameter values measured in this study. In Chapter 3 I compared a non-cyclic snowshoe hare population on Jacquot Island in Kluane Lake, with a cyclic population on the mainland, 40 km to the SE. I use trapping data from both mainland and island sites, for a period that included population increase, peak, and decline (1977-85) to test hypotheses of conditions sufficient to cause a hare population cycle. I also presented results from a radio-telemetry study, conducted on both mainland and island during a population low on the mainland (1984-85). The hypothesis that high rates of recruitment followed by low rates of recruitment, is sufficient to cause a cycle was not supported. Data presented was consistent with hypotheses that any one of the following conditions was sufficient to cause the hare cycle: 1. High rates of survival followed by low rates of survival, particularly of juveniles 2. Delayed density-dependent predation 3. Periodic food shortage.