Cyclic fluctuations in abundance exhibited by some mammalian populations in northern habitats ("population cycles") are key processes in the functioning of many boreal and tundra ecosystems. Understanding population cycles, essentially demographic processes, necessitates discerning the demographic mechanisms that underlie numerical changes. Using mark-recapture data spanning 5 population cycles (1977-2017), we examined demographic mechanisms underlying the 9-10-year cycles exhibited by snowshoe hares (Lepus americanus Erxleben) in southwestern Yukon, Canada. Snowshoe hare populations always decreased during winter and increased during summer; the balance between winter declines and summer increases characterized the four, multiyear cyclic phases: increase, peak, decline, and low. Little or no recruitment occurred during winter, but summer recruitment varied markedly across the 4 phases with the highest and lowest recruitment observed during the increase and decline phase, respectively. Population crashes during the decline were triggered by a substantial decline in winter survival and by a lack of subsequent summer recruitment. In contrast, initiation of the increase phase was triggered by a 2-fold increase in summer recruitment abetted secondarily by improvements in subsequent winter survival. We show that differences in peak density across cycles is explained by differences in overall population growth rate, amount of time available for population growth to occur, and starting population density. Demographic mechanisms underlying snowshoe hare population cycles were consistent across cycles in our study site but we do not yet know if similar demographic processes underlie population cycles in other northern snowshoe hare populations.

中文翻译：

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雪兔种群周期的人口统计

北部栖息地的一些哺乳动物种群（“种群周期”）表现出的丰度周期性波动是许多北方和苔原生态系统功能的关键过程。理解人口周期，本质上是人口过程，需要辨别数字变化背后的人口机制。使用跨越 5 个人口周期（1977-2017 年）的标记-重新捕获数据，我们研究了加拿大育空地区西南部雪鞋野兔（美洲兔）展示的 9-10 年周期的人口统计机制。雪鞋野兔的数量总是在冬季减少而在夏季增加；冬季下降和夏季增加之间的平衡表现为四个多年循环阶段：增加、高峰、下降和低谷。冬季很少或没有招募，但夏季招募在 4 个阶段中显着变化，分别在上升和下降阶段观察到最高和最低招募。下降期间的人口崩溃是由冬季生存率大幅下降和随后的夏季招募缺乏引发的。相比之下，增加阶段的开始是由夏季招募增加 2 倍引发的，其次是随后冬季存活率的改善。我们表明，跨周期峰值密度的差异可以通过总体人口增长率、人口增长发生的可用时间和起始人口密度的差异来解释。