Survival of juvenile hares during a cyclic population increase

1998 ◽  
Vol 76 (10) ◽  
pp. 1949-1956 ◽  
Author(s):  
Elizabeth A Gillis
Keyword(s):  
Cause Of Death ◽  
Food Availability ◽  
Survival Rates ◽  
Lepus Americanus ◽  
Population Increase ◽  
Differential Survival ◽  
Proximate Cause ◽  
Supplemental Food ◽  
Snowshoe Hares ◽  
And Control

Snowshoe hares (Lepus americanus) are multilittered synchronous breeders that produce up to four distinct litters of young each summer. I used radiotelemetry to determine the effects of juvenile cohort (i.e., litter group) and food availability on postweaning survival of hares in the southwestern Yukon during the increase phase of a hare cycle. During the study, I monitored 86 juvenile hares from control areas and areas in which supplemental food was provided. Twenty-eight-day survival did not differ between food addition and control areas for any juvenile cohort, and survival rates of juveniles (all cohorts combined) did not differ significantly from those of adults (juveniles: 0.91 per 28 days; adults: 0.93 per 28 days). However, when examined by juvenile cohort, survival of third and fourth litters was significantly lower than that of adults and first and second litters. These differences were the result of differential survival among the juvenile cohorts during a 3-month period in the fall (September-November). Predation was the primary proximate cause of death for weaned juvenile hares, accounting for 86% of deaths.

Impact of helminth parasitism on a snowshoe hare population in central Wisconsin: a field experiment

1995 ◽  
Vol 73 (10) ◽  
pp. 1891-1898 ◽  
Author(s):  
Sara E. M. Bloomer ◽  
Thomas Willebrand ◽  
Ingegerd M. Keith ◽  
Lloyd B. Keith
Keyword(s):  
Survival Rates ◽  
Snowshoe Hare ◽  
Marrow Fat ◽  
Proximate Cause ◽  
Risk Of Death ◽  
Snowshoe Hares ◽  
Condition Indices ◽  
Time Specific ◽  
And Control ◽  
Hare Population

We tested the hypothesis that helminth parasitism is demographically significant to a noncyclic population of snowshoe hares (Lepus americanus) near the species' geographic boundary in central Wisconsin (U.S.A.). During November 1988 to December 1991, we injected 93 individuals (≥760 g, aged ≥2 months) with anthelmintics: Ivermectin for nematode and Droncit for cestode infections. We injected 98 control hares with propylene glycol, the common vehicle for both drugs. All treated and control hares were radio-collared with mortality-sensing transmitters and monitored daily to weekly from the ground or air. Prevalence and intensity of lungworms (Protostrongylus boughtoni), intestinal worms (Nematodirus triangularis), and stomach worms (Obeliscoides cuniculi) were markedly reduced by Ivermectin treatment. No other nematodes were found to be present. Treatment with Droncit to remove intestinal cestodes was apparently unnecessary, as prevalence among necropsied untreated hares and controls was just 10%. We compared body-condition indices (mass changes, response to trap stress, and bone-marrow fat), reproduction (pregnancy rate and litter size), home-range sizes, and time-specific survival rates of anthelmintic-treated versus control hares. None of these demographic variables differed significantly between treated and control cohorts, nor was there any evidence that parasitism increased the risk of death from predation, which was the proximate cause of 96% of all natural mortalities. We conclude that helminth parasitism played no detectable role in the dynamics of this Wisconsin snowshoe hare population.

Dynamics of a snow shoe hare population in fragmented habitat

1993 ◽  
Vol 71 (7) ◽  
pp. 1385-1392 ◽  
Author(s):  
Lloyd B. Keith ◽  
Sara E. M. Bloomer ◽  
Tomas Willebrand
Keyword(s):  
Patch Size ◽  
Canis Latrans ◽  
Lepus Americanus ◽  
Fragmented Habitat ◽  
Proximate Cause ◽  
Lower Survival ◽  
The Third ◽  
Snowshoe Hares ◽  
Poorly Drained Soils ◽  
Hare Population

During November 1988 – December 1991 we livetrapped, radio-collared, and monitored the survival, reproduction, and movements of snowshoe hares (Lepus americanus) in highly fragmented habitat near the species' geographic limit in central Wisconsin. Our 7 study areas centered on 5- to 28-ha patches of prime habitat: dense stands of willow (Salix), alder (Alnus), and regenerating aspen (Populus) on poorly drained soils. Maximum hare densities averaged 1.6 – 0.8/ha, and were unrelated to patch size. Rapid declines to extinction occurred on 3 of the 5 smallest study areas; on another, where extinction seemed imminent, juvenile ingress restored the population. On the 2 largest areas (23 – 28 ha of prime habitat) hare populations were stationary during the first 2 years, but declined by 50 – 70% in the third as mean annual (September – August) survival of radio-collared hares fell from 0.27 (1988 – 1990) to 0.07 (1990 – 1991). Annual survival on the 3 extinction sites averaged just 0.015 compared with 0.179 elsewhere. Reproduction did not differ between small (5 – 7 ha) vs. larger (23 – 28 ha) patches nor between years. Estimated dispersal of adult and juvenile hares from the 5 small study areas was twice as high as from the 2 larger, viz. 16 vs. 35% annually. Dispersers appeared to have markedly lower survival. Predation, chiefly by coyotes (Canis latrans), was the proximate cause of 96% (117 of 122) of natural deaths among radio-collared hares, and was therefore the overwhelming determinant of survival and thus population trend. Results of this study suggest that probabilities of extinction in such fragmented habitat depend importantly on patch size and attendant hare numbers; i.e., fall populations of < 10 hares frequenting patches of prime habitat ≤ 5 ha are not likely to persist long without ingress.

The role of dispersal in the population dynamics of snowshoe hares

1985 ◽  
Vol 63 (1) ◽  
pp. 106-115 ◽  
Author(s):  
Stan Boutin ◽  
B. S. Gilbert ◽  
Charles J. Krebs ◽  
A. R. E. Sinclair ◽  
J. N. M. Smith
Keyword(s):  
Population Dynamics ◽  
Small Mammals ◽  
Lepus Americanus ◽  
Population Increase ◽  
Dispersal Rate ◽  
Population Densities ◽  
Control Grid ◽  
Snowshoe Hares ◽  
Kluane Lake

We monitored dispersal of snowshoe hares (Lepus americanus) at Kluane Lake, Yukon, during a population increase, peak, and decline. Dispersal was measured by recording the number of immigrants to a removal grid and by tracking radiocollared individuals. The observed decline was not due to dispersal, as a maximum of 28% of all losses of radiocollared animals was due to dispersal. Dispersal rate (as measured by number of immigrants to the removal grid per individual on the control grid) was negatively correlated (−0.51, P < 0.01) with the rate of population increase. Highest dispersal rates occurred in the winters when hare populations were at peak and early decline densities. Dispersers at this time were lighter in weight than residents. We discuss our results in light of current hypotheses attempting to explain dispersal in cyclic small mammals and conclude that our results are consistent with the hypothesis that food shortage is responsible for increased rates of dispersal at peak population densities Comparison of dispersal, as monitored by radiotelemetry, versus immigration to a removal grid, suggests that removal grids overestimate dispersal, particularly at high densities when removal grids may attract animals because food supplies are relatively favorable there.

Differential sex-related winter energetics in free-ranging snowshoe hares (Lepus americanus)

2016 ◽  
Vol 94 (2) ◽  
pp. 115-121 ◽  
Author(s):  
E. Ellsworth ◽  
M.R. Boudreau ◽  
K. Nagy ◽  
J.L. Rachlow ◽  
D.L. Murray
Keyword(s):  
Energy Expenditure ◽  
Food Availability ◽  
Lepus Americanus ◽  
Energetic Cost ◽  
Food Supplementation ◽  
Natural Food ◽  
Daily Energy Expenditure ◽  
Snowshoe Hares ◽  
Daily Energy ◽  
Free Ranging

Animals spend considerable time and energy acquiring food to meet their metabolic requirements, but if energetic or fitness costs are substantive, such as during winter, then some individuals may limit daily energy expenditure by reducing foraging duration. To date, the prevalence and magnitude of such compensatory foraging responses are poorly known. We examined energy balance compensation in free-ranging snowshoe hares (Lepus americanus Erxleben, 1777) via a food supplementation experiment to determine whether individuals reduced their daily energy expenditure (DEE) and activity periods in response to increased food availability. Overall, food supplementation had no effect on diel activity patterns, although males had higher DEE compared with females. During early and mid-winter, hares did not alter their activity periods in response to food supplementation, but during late winter, when natural food availability declined, food-supplemented females (but not males) were ∼11% less active compared with controls. Natural food likely was sufficient and could have been acquired at relatively low energetic cost, but because males likely have higher DEE due to mating behavior whereas females may limit their activity (and thus DEE) to reduce predation risk, we conclude that gender-specific life-history demands can over-ride predicted responses to supplemental food when baseline food abundance is adequate.

Risk of parasite-induced predation: an experimental field study on Townsend's voles (Microtus townsendii)

2002 ◽  
Vol 80 (7) ◽  
pp. 1286-1292 ◽  
Author(s):  
Harald Steen ◽  
Mary Taitt ◽  
Charles J Krebs
Keyword(s):  
Parasite Prevalence ◽  
Control Groups ◽  
Red Grouse ◽  
Proximate Cause ◽  
Snowshoe Hares ◽  
Causes Of Mortality ◽  
Parasite Infestation ◽  
Breeding Seasons ◽  
And Control ◽  
Microtus Townsendii

Studies of causes of mortality in rodents, snowshoe hares, and red grouse show that many individuals succumb to predation and few die from starvation or parasite infestation. Predation may be the proximate cause of death and factors like parasite infestation and starvation could facilitate predation. Our aim was to test whether Townsend's voles, Microtus townsendii, experimentally rid of parasites are less likely to be killed by predators than are control voles. During two breeding seasons we treated half of the adults caught at Boundary Bay, British Columbia, Canada, with the anthelmintic Ivomec® and left the other half as controls. Voles were randomly assigned to the treatment and control groups. Predators killed 5 of 23 treated voles and 11 of 26 control voles in 1998. In 1997 predators killed 3 of 17 treated voles and 2 of 18 control voles. Vole density was higher in 1998 than in 1997 and predation was the main cause of mortality in both years. Survival of control voles was lower in 1998 than in 1997, indicating lower predation pressure in 1997 than in 1998. Botfly prevalence and intensity were low and similar in both years. We speculate that the lack of treatment effect in 1997 could have been due to lower overall parasite prevalence in that year than in 1998, resulting in relatively higher susceptibility of voles to predation. Parasite-induced predation reduced monthly survival by 17% in 1998.

Differential mortality of sympatric snowshoe hares and cottontail rabbits in central Wisconsin

1993 ◽  
Vol 71 (8) ◽  
pp. 1694-1697 ◽  
Author(s):  
Lloyd B. Keith ◽  
Sara E. M. Bloomer
Keyword(s):  
Low Temperatures ◽  
Escape Behavior ◽  
Survival Rates ◽  
Differential Mortality ◽  
Interspecific Difference ◽  
High Survival ◽  
Sylvilagus Floridanus ◽  
Proximate Cause ◽  
Snowshoe Hares ◽  
Foot Loading

During 1990 and 1991 we livetrapped and radio-collared cottontail rabbits (Sylvilagus floridanus) and snowshoe hares (Lepus americanus) on five sites (three in lowland deciduous cover, two in conifer bogs) in central Wisconsin. The survival rates of these sympatric cottontails and snowshoes were equally high during snow-free periods from mid-March through October. With the onset of persistent snow cover (mean depth 20 cm) and low temperatures (mean daily minimum −14 °C) in November 1991, the 60-day survival rate of cottontails plummeted from 0.89 to 0.18 (P < 0.01) whereas snowshoe survival declined only moderately from 0.84 to 0.63 (P = 0.19). This interspecific difference reflected continued high survival of snowshoes (0.80), but not of cottontails (0.15), in the conifer bogs. Predation, primarily by coyotes, was the proximate cause of 37 of 39 rabbit and hare deaths, and was thus the overwhelming determinant of survival. We speculate that where persistent snow and low temperatures characterize winter, the cottontail's greater foot loading, brown coloration, and escape behavior markedly increase its vulnerability to predators. This probably explains the absence of cottontails from the forests of northern Wisconsin.

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.

Inbreeding effects among inbred and outbred laboratory colonies of Peromyscus maniculatus

1992 ◽  
Vol 70 (4) ◽  
pp. 820-824 ◽  
Author(s):  
David O. Ribble ◽  
John S. Millar
Keyword(s):  
Performance Measures ◽  
Reproductive Performance ◽  
First Generation ◽  
Peromyscus Maniculatus ◽  
Survival Rates ◽  
Natural Populations ◽  
Outbreeding Depression ◽  
Sibling Pairs ◽  
Laboratory Colonies ◽  
And Control

We examined the effects of sibling matings upon reproductive performance among inbred and outbred laboratory colonies of Peromyscus maniculatus. The inbred colony was founded by 12 females collected from one locality in Alberta and bred for 20 generations, with 35–45 pairs each generation. The outbred colony consisted of first-generation mice born of wild-caught females from diverse areas in Alberta. Consistent with theoretical expectations, there were no differences in reproductive performance between sibling and control (outbred) pairs within the inbred colony of mice. In contrast, sibling pairs had significantly fewer young per litter than control pairs within the outbred colony. Reproductive performance measures (proportion breeding, days from pairing to first litter, number of litters, and total number of offspring produced) were also significantly lower among sibling pairs from the outbred colony than among sibling pairs from the inbred colony. Lastly, we predicted that reproductive performance of the control pairs from the outbred colony would be less than that of control pairs from the inbred colony, due to outbreeding depression. Contrary to our predictions, average litter survival rates were greatest among the outbred colony control pairs. We suggest that the benefits of inbreeding or outbreeding extend broadly across the inbreeding–outbreeding continuum in natural populations of northern Peromyscus.

High-dose enoxaparin in the treatment of abdominal angiostrongyliasis in Swiss mice

2017 ◽  
Vol 92 (6) ◽  
pp. 662-667 ◽  
Author(s):  
A.S.S. Sandri ◽  
R. Rodriguez ◽  
M.M. Costa ◽  
S.M. Porto ◽  
D. Schwingel ◽  
...  
Keyword(s):  
Survival Rates ◽  
Mesenteric Arteries ◽  
High Dose ◽  
Control Groups ◽  
Intestinal Infarction ◽  
Intestinal Lesions ◽  
Group 2 ◽  
High Doses ◽  
And Control ◽  
Group 1

AbstractAbdominal angiostrongyliasis (AA) is caused by Angiostrongylus costaricensis, which inhabits mesenteric arteries. There is no drug treatment for AA, and since intestinal infarction due to thrombi is one of the main complications of the disease, the use of anticoagulants may be a treatment option. Thus, we aimed to assess the effect of high doses of enoxaparin on the prevention of ischaemic intestinal lesions and on the survival of mice infected with A. costaricensis. Twenty-four mice were infected with L3 of A. costaricensis and divided equally into two groups: Group 1, control treated with placebo, and Group 2, treated daily with enoxaparin (2.5 mg/kg) for 50 days. All mice were subjected to necropsy and histological analysis. The results from gross and microscopic assessments showed no variation in the prevalence of lesions between the groups. An analysis was also performed among survivors and non-survivors, showing that animals that died often presented lesions, such as granulation tissue in the serosa, and intestinal infarction and adhesion. The mortality rate did not vary between the enoxaparin-treated and control groups. Thus, we showed that high doses of enoxaparin have no protective effect against AA, as the survival rates and lesions of mice did not vary between the treated and control groups. Considering that the use of prophylactic doses was also shown to be ineffective in a previous study, we do not recommend the use of enoxaparin for AA treatment.

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