Cyclic dynamics of snowshoe hares on a small island in the Yukon

(5 km2) in Kluane Lake, southwestern Yukon, and on nearby mainland sites. Jacquot Island hares averaged twice the density of mainland control populations and, although they show 10-year cycles, fluctuate with much lower amplitude than mainland populations. Three separate intensive studies over 6 years attempted to determine what caused these dif-ferences. We tested two hypotheses to explain the dynamics. Reproductive rates of hares were similar on Jacquot Island and the mainland. Adult survival rates were higher on the island in most years, with the exception of years of popula-tion decline. Juvenile survival rates from 0 to 30 days of life were much higher on the island than on the mainland ex-cept for decline summers. The adult- and juvenile-survival differences between the island and the mainland were explained most consistently by predation. Improved survival on the island is correlated with a reduction in the numbers and types of predators found on Jacquot Island compared with the mainland. In particular, red squirrels were rare on Jacquot Island, arctic ground squirrels were absent, and the larger predators, like lynx and great-horned owls, were spo-radic in occurrence on this small island. Résumé: Des populations de lièvres d’amérique (Lepus americanus) ont été suivies de 1977 à 2001 sur l’Île Jacquot (5 km2) au Lac Kluane (sud-ouest du Yukon), ainsi qu’à des sites sur la terre ferme, à proximité. Les densités de liè-vres sur l’Île Jacquot équivalent en moyenne au double de celles des populations témoins sur la terre ferme et, quoique les premières fluctuent selon un cycle de 10 ans, leurs fluctuations sont d’une amplitude de beaucoup inférieure à cel