Mammal population cycles: evidence for intrinsic differences during snowshoe hare cycles

A Sinclair, C Chitty, C Stefan

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)


Some mammals in high northern latitudes show regular population cycles. In snowshoe hares (Lepus americanus), these occur every 9–10 years. One hypothesis proposes extrinsic causes such as food shortage or predation. The other proposes intrinsic causes through different morphs that alternate between different phases of the cycle. The morphs should differ in behaviour or physiology. This hypothesis predicts that animal lineages bred from high and low phases of the population cycle should differ in reproduction and survivorship. In a 16-year breeding program, lineages of purebred high-phase female hares had reduced reproductive rates relative to those of purebred low-phase females, resulting in extinction of high-phase lineages. Reproductive output declined with age in high- but not low-phase animals. These lineages also differed in longevity and senescence. These results are consistent with the intrinsic hypothesis and suggest a mechanism for alternating population densities that could work synergistically with extrinsic causes like predation and food shortage
Original languageEnglish
Pages (from-to)216-220
Number of pages5
JournalCanadian Journal of Zoology
Issue number2
Publication statusPublished - 2003
Externally publishedYes


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