THE GEOMETRY OF A POPULATION CYCLE: A MECHANISTIC MODEL OF SNOWSHOE HARE DEMOGRAPHY

Ecology ◽  
2001 ◽  
Vol 82 (3) ◽  
pp. 814-830 ◽  
Author(s):  
Aaron A. King ◽  
William M. Schaffer
Keyword(s):  
Mechanistic Model ◽  
Population Cycle ◽  
Snowshoe Hare

Reproductive change in the 10-year cycle of snowshoe hares

1979 ◽  
Vol 57 (2) ◽  
pp. 375-390 ◽  
Author(s):  
John R. Cary ◽  
Lloyd B. Keith
Keyword(s):  
Pregnancy Rate ◽  
Litter Size ◽  
Weight Change ◽  
Ovulation Rate ◽  
Population Cycle ◽  
Snowshoe Hare ◽  
Cyclic Variation ◽  
Reproductive Parameters ◽  
Snowshoe Hares ◽  
Hare Population

Reproduction was monitored during a 16-year study of snowshoe hare (Lepus americanus) populations near Rochester, Alberta. Pregnancy rate, ovulation rate, and litter size changed markedly between successive litters within the breeding season; these parameters were thus further categorized by litter in our analyses. Most reproductive components varied significantly between years; a significant '10-year' periodicity was the dominant source of this variation. The cyclic fluctuations of reproductive parameters were broadly synchronous and tended to precede the population cycle by about 3 years, thereby producing a range in potential natality annually of 7.5 to 17.9 young per female. The year-to-year variability of pregnancy rate, ovulation rate, and litter size was markedly larger in the later litters than in the early ones. Paunched weight, mean age, incidence of endoparasites, liver and spleen weights, and midwinter-to-spring weight change also possessed significant 10-year cycles; paunched weight cycled directly with the hare population, but the others cycled either directly with or counter to reproduction. We believe that the correspondence between midwinter-to-spring weight change and reproduction implicates winter nutrition as the primary cause of the cyclic variation. Onset of spring accounted for a significant amount of variability in onset of breeding, adding to that due to the periodic change.

scholarly journals The enigma of the 10-year wildlife population cycle solved? Evidence that the periodicity and regularity of the cycle are driven by a lunar zeitgeber

2015 ◽  
Vol 128 (4) ◽  
pp. 327 ◽  
Author(s):  
Herbert L. Archibald
Keyword(s):  
Population Cycles ◽  
Amplitude Distribution ◽  
Ultraviolet B ◽  
Population Cycle ◽  
Snowshoe Hare ◽  
Lynx Lynx ◽  
Half Cycle ◽  
Ruffed Grouse ◽  
Lynx Canadensis ◽  
Wildlife Population

Despite nearly 100 years of research, the periodicity and regularity of the 10-year wildlife population cycle remain an enigma. This paper presents the hypothesis that the 9.3-year nodal half-cycle of the moon is the zeitgeber (“time-giver”) of the 10-year wildlife population cycle. The period of the population cycles of the Snowshoe Hare (Lepus americanus) and Ruffed Grouse (Bonasa umbellus) is close to 9.3 years. These wildlife cycles have stayed closely in phase with the 9.3-year nodal half-cycle for 150 years. Population density of the Snowshoe Hare and Ruffed Grouse is inversely related to a 9.3-year cycle of the moon's tidal force. There is also a 9.3-year cycle of “nights without darkness” at the equinoxes, in which the full moon rises before sunset and sets after sunrise the following morning in certain years. Snowshoe Hare and Ruffed Grouse cycles are positively correlated with this phenomenon. The nodal cycle provides explanations for the key features of the 10-year wildlife cycle: regularity, periodicity, amplitude, distribution, and synchrony. Population models based solely on the nodal cycle account for 62% of the variation in the Canada Lynx (Lynx canadensis) cycle and 37% in the Ruffed Grouse cycle. The mechanism(s) by which herbivore cycles might be entrained by the lunar nodal cycle could involve a cyclic effect on factors including predation, stress, photoperiod, phenology, temperature, cloudiness, ultraviolet B radiation, cosmic rays, and food plant quality.

Snowshoe hare adrenal weights in relation to population density

1977 ◽  
Vol 55 (3) ◽  
pp. 634-637 ◽  
Author(s):  
E. O. Höhn ◽  
J. G. Stelfox
Keyword(s):  
Adrenal Weight ◽  
Gastric Ulcers ◽  
Population Cycle ◽  
Snowshoe Hare ◽  
Lower Body ◽  
Population Densities ◽  
The Third ◽  
Snowshoe Hares ◽  
Body Weights ◽  
Hare Population

Adrenal and body weights of snowshoe hares from three areas in which hare population densities differed markedly were determined in a search for evidence of adrenal enlargement in the course of the population cycle. In the first area hares were in a sudden decline after a peak. Dead hares were found there in some numbers. Hare populations in the other two areas were still rising (population peaks occurred 18 months after sampling), but hare density was considerably greater in the second as compared with the third area. There were no significant differences in absolute adrenal weight between any of the groups. Relative adrenal weights were also similar, except for significantly higher relative adrenal weights in hares found dead as compared with those shot, but this was apparently due merely to the lower body weights of animals found dead compared with those killed. There was no evidence of significant differences in relative adrenal weight according to sex or age. No gastric ulcers were found in 26 hares taken from a population at the peak of the cycle.

Browse site selection by snowshoe hares: effects of food supply and predation risk

2005 ◽  
Vol 83 (2) ◽  
pp. 280-292 ◽  
Author(s):  
K E Hodges ◽  
A R.E Sinclair
Keyword(s):  
Site Selection ◽  
Food Supply ◽  
Foraging Behaviour ◽  
Population Cycles ◽  
Distribution Patterns ◽  
Pressure Change ◽  
Population Cycle ◽  
Snowshoe Hare ◽  
Snowshoe Hares ◽  
Survival And Reproduction

If snowshoe hares (Lepus americanus Erxleben, 1777) change their foraging behaviour through the population cycle as food supply and predation pressure change, these shifts could contribute to their population cycles by affecting survival and reproduction. We examined whether hares change their foraging movements and browse site selection in response to manipulations of food addition and predator reduction during a cyclic low phase. Snowshoe hares on sites with supplemental rabbit chow ate fewer species per site and preferred to browse in slightly denser cover than unfed hares. Differences in foraging behaviour were linked to season and site characteristics. Snowshoe hares moved similar distances and spent similar amounts of time per browse site in the presence and absence of terrestrial predators. Hares protected from predators used slightly more browse sites in thick cover, but this pattern was partially due to differences in availability. The absence of terrestrial predators had little effect on snowshoe hare foraging behaviour; instead, browse distribution patterns explained most of the behavioural variation. Thus, the predicted patterns in response to the manipulations did not occur, and our results challenge the idea that changes in snowshoe hare foraging behaviour contribute to their cyclic dynamics.

Winter diet of marten during a snowshoe hare decline

1996 ◽  
Vol 74 (3) ◽  
pp. 456-466 ◽  
Author(s):  
Kim G. Poole ◽  
Ron P. Graf
Keyword(s):  
Northern Region ◽  
Southern Region ◽  
Population Cycle ◽  
Snowshoe Hare ◽  
Corpora Lutea ◽  
Sex Structure ◽  
Winter Diet ◽  
Snowshoe Hares ◽  
Age And Sex ◽  
Prey Items

We examined the winter diet of marten (Martes americana) from northern (65–67°N) and southern (60–62°N) regions of the western Northwest Territories from 1988–1989 to 1993–1994 during a decline in snowshoe hare (Lepus americanus) abundance that started in 1990. We used 4256 marten carcasses collected from trappers to examine changes in diet, productivity, age and sex structure of the harvest, and body and reproductive indices. Arvicoline rodents formed the greatest proportion (41–95% occurrence of total prey items) of the annual winter diet in both regions and snowshoe hares constituted 1–39% of prey items. Snowshoe hares constituted 3–64% of the diet when expressed as biomass. Dietary proportions of arvicolines increased and snowshoe hares decreased with time in the northern region but not in the southern region. Female marten took proportionately more arvicolines and males took more snowshoe hares. Juvenile marten took proportionately more snowshoe hares, while adults took more arvicolines. The proportion of juvenile marten in the harvest declined in both regions between 1991–1992 and 1993–1994. The ratio of juveniles to adult females in the harvest also declined with time in the southern region but not in the northern region. The amount of omental fat declined with time for most age and sex classes. Ovulation rates (as determined by counts of corpora lutea) declined with time among yearlings, and among adults from the southern region but not in the northern region. In utero litter size did not change. We suggest that the snowshoe hare population cycle has a significant impact on marten populations in the northern boreal forest.

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

2003 ◽  
Vol 81 (2) ◽  
pp. 216-220 ◽  
Author(s):  
A R.E Sinclair ◽  
Dennis Chitty ◽  
Carol I Stefan ◽  
Charles J Krebs
Keyword(s):  
Reproductive Output ◽  
Population Cycles ◽  
Food Shortage ◽  
Population Cycle ◽  
Snowshoe Hare ◽  
Population Densities ◽  
Northern Latitudes ◽  
Snowshoe Hares ◽  
Reproductive Rates ◽  
High Phase

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.

Does predation risk cause snowshoe hares to modify their diets?

2003 ◽  
Vol 81 (12) ◽  
pp. 1973-1985 ◽  
Author(s):  
K E Hodges ◽  
A R.E Sinclair
Keyword(s):  
Species Composition ◽  
Predation Risk ◽  
Sublethal Effects ◽  
Population Cycle ◽  
Food Supplementation ◽  
Snowshoe Hare ◽  
Supplemental Food ◽  
Snowshoe Hares ◽  
Wide Range ◽  
Mammalian Predators

Snowshoe hares (Lepus americanus) undergo a 10-year population cycle with several years of low densities. Several authors have suggested that snowshoe hares modify their foraging behaviour to reduce predation risk during the low phase, resulting in protein-poor diets and poor body condition. We test that idea by using a factorial manipulation of food supplementation and predator reduction and by examining the species composition, browse size, and nutritional quality of snowshoe hare diets during 3 years of low snowshoe hare abundance in southwestern Yukon. Our results negate the hypothesis that snowshoe hares change their diets in response to mammalian predators during the cyclic low phase. Snowshoe hares on the different treatments had diets that differed in species composition and twig sizes, but protected hares did not have higher protein diets than unprotected hares. Snowshoe hares with access to supplemental food ate more fibrous and lower protein natural browse than unfed hares, showing that they did not choose diets primarily for protein content. Instead, snowshoe hares converted a wide range of forage availabilities into similar intakes of protein and fibre, despite variation in predator presence. Our results suggest that snowshoe hares select their diets to balance the protein and fibre contents. Although sublethal effects of predators may influence cyclic dynamics, our results show that such a feedback does not occur via a nutritional mechanism, counter to previous suggestions.

Restriction of Access to Dark State: A New Mechanistic Model for Heteroatom-Containing AIE Systems

2019 ◽  
Author(s):  
Yujie Tu ◽  
Junkai Liu ◽  
Haoke Zhang ◽  
Qian Peng ◽  
Jacky W. Y. Lam ◽  
...  
Keyword(s):  
Excited States ◽  
Radiative Decay ◽  
Molecular Design ◽  
Mechanistic Model ◽  
Zinc Ion ◽  
Easy Access ◽  
Triplet States ◽  
Dark State ◽  
Ion Probe ◽  
Π State

Aggregation-induced emission (AIE) is an unusual photophysical phenomenon and provides an effective and advantageous strategy for the design of highly emissive materials in versatile applications such as sensing, imaging, and theragnosis. "Restriction of intramolecular motion" is the well-recognized working mechanism of AIE and have guided the molecular design of most AIE materials. However, it sometimes fails to be workable to some heteroatom-containing systems. Herein, in this work, we take more than one excited state into account and specify a mechanism –"restriction of access to dark state (RADS)" – to explain the AIE effect of heteroatom-containing molecules. An anthracene-based zinc ion probe named APA is chosen as the model compound, whose weak fluorescence in solution is ascribed to the easy access from the bright (π,π*) state to the closelying dark (n,π*) state caused by the strong vibronic coupling of the two excited states. By either metal complexation or aggregation, the dark state is less accessible due to the restriction of the molecular motion leading to the dark state and elevation of the dark state energy, thus the emission of the bright state is restored. RADS is found to be powerful in elucidating the photophysics of AIE materials with excited states which favor non-radiative decay, including overlap-forbidden states such as (n,π*) and CT states, spin-forbidden triplet states, which commonly exist in heteroatom-containing molecules.

Sign in / Sign up

Export Citation Format

Share Document