Reproductive change in the 10-year cycle of snowshoe hares

Cary, John R.; Keith, Lloyd B.

doi:10.1139/z79-044

Cited by 90 publications

(125 citation statements)

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“…Hare reproductive rates fluctuate dramatically over the 10-year cycle (Cary and Keith 1979;Stefan and Krebs 2001) but changes occur in a similar way on the island and the mainland. Thus, survival differences must underlie the demographic patterns of the island population.…”

Section: Discussionmentioning

confidence: 99%

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

Zimmerling¹,

Jardine²,

Trostel³

et al. 2002

Can. J. Zool.

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Snowshoe hare (Lepus americanus) populations were monitored from 1977 to 2001 on Jacquot Island (5 km 2 ) 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 differences. 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 population decline. Juvenile survival rates from 0 to 30 days of life were much higher on the island than on the mainland except 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 sporadic in occurrence on this small island. 2 ) 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 celles des populations de terre ferme. Les causes de ces différences ont été examinées au cours de trois études intensives différentes s'échelonnant sur 6 ans. Nous avons testé deux hypothèses quant à la dynamique de ces populations. Les taux de reproduction sur l'île Jacquot et sur la terre ferme sont similaires. La plupart des années, le taux de survie des adultes est plus grand sur l'île que sur la terre ferme, sauf durant les années où les populations sont en déclin. Le taux de survie de 0 à 30 jours chez les juvéniles est beaucoup plus grand sur l'île que sur la terre ferme, excepté durant les étés de déclin. C'est l'effet des prédateurs résidants qui explique le mieux les différences de taux de survie entre les lièvres de l'île et ceux de la terre ferme, aussi bien chez les adultes que chez les juvéniles. Le meilleur taux de survie des lièvres sur l'île associé à une guilde de prédateurs plus pauvre en nombres et en espèces que celle des sites la terre ferme. Plus particulièrement, les écureuils roux sont rares sur cette petite île, les spermophiles arctiques y sont absents, et les plus gros prédateurs comme le lynx et le grand-duc ne s'y trouvent que sporadiquement. 1450Krebs et al.

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Section: Discussionmentioning

confidence: 99%

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

Zimmerling¹,

Jardine²,

Trostel³

et al. 2002

Can. J. Zool.

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“…For snowshoe hares, reproductive output is lower for several years before the peak density and through the population decline [43,44] as females produce fewer than the maximum of four litters. This can reduce reproductive output by 50% (two versus four litters per year).…”

Section: Changes In Mortality Versus Reproductionmentioning

confidence: 99%

Population cycles: generalities, exceptions and remaining mysteries

Myers¹

2018

Proc. R. Soc. B.

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Population cycles are one of nature's great mysteries. For almost a hundred years, innumerable studies have probed the causes of cyclic dynamics in snowshoe hares, voles and lemmings, forest Lepidoptera and grouse. Even though cyclic species have very different life histories, similarities in mechanisms related to their dynamics are apparent. In addition to high reproductive rates and density-related mortality from predators, pathogens or parasitoids, other characteristics include transgenerational reduced reproduction and dispersal with increasing-peak densities, and genetic similarity among populations. Experiments to stop cyclic dynamics and comparisons of cyclic and noncyclic populations provide some understanding but both reproduction and mortality must be considered. What determines variation in amplitude and periodicity of population outbreaks remains a mystery.

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“…There are several competing hypotheses to explain the hare cycle. The most widely accepted explanation is that winter food shortage (Keith 1974) depresses hare reproduction (Carey and Keith 1979) at the population peak and starts the cyclic downturn, and hare numbers are subsequently further reduced due to predation (Keith et al 1984). Gilpin (1973) and Schaffer (1984) modelled harvest data mathematically, and concluded that the cycle is more complex than a simple predator-prey interaction, involving at least a third additional factor.…”

Section: Principal Threatsmentioning

confidence: 99%