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.

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.

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.

Food supplementation experiments revisited: verifying that supplemental food is used by its intended recipients

2007 ◽  
Vol 85 (6) ◽  
pp. 679-685 ◽  
Author(s):  
A.J. Wirsing ◽  
D.L. Murray
Keyword(s):  
Population Level ◽  
Food Supplementation ◽  
Natural Food ◽  
Supplemental Food ◽  
Snowshoe Hares ◽  
Extra Food ◽  
Study Sites ◽  
Natural Foods ◽  
And Control ◽  
Free Ranging

Field-based food supplementation experiments can determine whether populations are limited by natural food availability. However, they may yield spurious results if added food is hoarded by dominants, exploited by immigrants, or delivered ineffectively. Surprisingly, population-level approaches accounting for these potential sources of bias have not been established. We explored responses of free-ranging snowshoe hares ( Lepus americanus Erxleben, 1777) to food supplementation by contrasting per capita browsing rates on three study sites with added food with those on three control sites during two winters. Food augmentation reduced foraging pressure by hares; this reduction was significant when browse species of high dietary importance were considered. By implication, hares on manipulated sites switched from favored natural foods to supplemental food, meaning that the extra food found its mark and was not heavily exploited by immigrants or hoarded by dominants. Demographic responses to food addition were not detected on the manipulated sites, indicating that the study population was not food limited. Given the success with which we detected the signal of supplementation and eliminated potential confounding factors, we suggest that future studies using food addition in the context of herbivore population dynamics would benefit from a more mechanistic approach; this may involve measurement of browsing rates on manipulated and control sites.

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.

The impact of variable predation risk on stress in snowshoe hares over the cycle in North America’s boreal forest: adjusting to change

Oecologia ◽  
2021 ◽  
Author(s):  
Sophia G. Lavergne ◽  
Charles J. Krebs ◽  
Alice J. Kenney ◽  
Stan Boutin ◽  
Dennis Murray ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Predation Risk ◽  
Snowshoe Hares ◽  
The Impact

Food supplementation and predation risk in harsh climate: interactive effects on abundance and body condition of tit species

Oikos ◽  
2016 ◽  
Vol 126 (6) ◽  
pp. 863-873 ◽  
Author(s):  
Chiara Morosinotto ◽  
Alexandre Villers ◽  
Rauno Varjonen ◽  
Erkki Korpimäki
Keyword(s):  
Predation Risk ◽  
Body Condition ◽  
Interactive Effects ◽  
Food Supplementation ◽  
Harsh Climate

scholarly journals DISTRIBUTION OF BRYOPHYTES OF AGALYK BASIN (KARATEPA MOUNTAINS OF ZERAVSHAN MOUNTAIN RANGE)

2015 ◽  
Vol 4 (2) ◽  
pp. 80-82
Author(s):  
Holmurod Akimovich Zhalov
Keyword(s):  
Species Composition ◽  
Point Of View ◽  
Mountain Range ◽  
Decayed Wood ◽  
Moss Species ◽  
Comparative Analyses ◽  
Wide Range ◽  
Identification Of Species ◽  
Characteristic Features ◽  
Research Period

From bryological point of view Zeravshan mountain range remains one of the least studied region. Identification of species composition of true mosses and their ecological-biological peculiarities were not earlier aimed for this region. In the territory of Agalyk basin Karatepa mountains can be divided into four types of substrates where moss species occur: soil, bark of living trees, decayed wood, stones. Characteristics of substrate groups become complicated due to wide range of ecological valency of moss species. Most species select not only one, but several substrates for their settling. During the research period in the soils of Agaliksay basin 20 species were recorded belonging to 13 genera and 10 family. On decayed wood 9 species were recorded belonging to 7 genera and 5 family. On the bark of living trees 15 moss species were recorded belonging to 8 genera and 6 family. Epilyte bryophytes occurred on rocky substrates. On rocky substrates of Agaliksay basin 34 moss species were recorded from 16 genera and 13 family. On the basis of results obtained during the study of substrate groups of mosses in Agaliksay basin, we have conducted comparative analyses of studied substrate groups with the purpose of determining their characteristic features.

Vegetation height and egg coloration differentially affect predation rate and overheating risk: an experimental test mimicking a ground-nesting bird

2012 ◽  
Vol 90 (6) ◽  
pp. 694-703 ◽  
Author(s):  
H. Gillis ◽  
B. Gauffre ◽  
R. Huot ◽  
V. Bretagnolle
Keyword(s):  
Predation Risk ◽  
Breeding Season ◽  
Nest Site Selection ◽  
Artificial Nests ◽  
Vegetation Height ◽  
Selective Pressures ◽  
Wide Range ◽  
Nest Microclimate ◽  
Egg Coloration ◽  
Ground Nesting

Avian eggs need to be laid in protected environments to develop and survive. Nest predation is known as the main cause of breeding failure for many birds, but nest microclimate conditions are also important for embryo development. These two selective pressures are particularly marked in ground-nesting birds. Vegetation height has been shown to be a critical factor for nest-site selection in ground-nesting birds because it can counteract predation and overheating simultaneously. It is therefore difficult to disentangle the respective influences of these risks on selection of a particular nest vegetation height. To develop a conceptual framework for understanding and predicting the relative effects of vegetation on predation and nest microclimate during a breeding season, we used vegetation height to manipulate differentially these two risks. We therefore exposed artificial nests to a wide range of vegetation heights, replicated the experimental tests during spring, and manipulated egg color to estimate predation risk. We confirmed that tall vegetation is relevant to protect unattended eggs against both risks. Whereas predation risk is stable for a given vegetation height, overheating risk presents inter- and intra-seasonal variations. Therefore, over a breeding season, for a given vegetation height, the respective strengths of the two risks are unbalanced and depends on egg coloration. The breeding strategy of ground-nesting birds thus should have been shaped by both selective pressures, but the ultimate choice may depend on the species-specific laying dates and alternative behavioral strategies for protecting the clutch. This study provides new perspectives to investigate avian parental behaviour.

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