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1.
    
Emerging diseases and expanding carnivore populations may have profound implications for ungulate harvest management and population regulation. To better understand effects of chronic wasting disease (CWD) and cougar (Puma concolor) predation, we studied mortality and recruitment of elk (Cervus elaphus) at Wind Cave National Park (WICA) during 2005–2009. We marked 202 elk (83 subadult M and 119 subadult and ad F) with Global Positioning System (GPS) collars, observed 28 deaths during 74,220 days of monitoring, and investigated 42 additional deaths of unmarked elk found dead. Survival rates were similar for males and females and averaged 0.863 (SE = 0.025) annually. Leading causes of mortality included hunting (0.065, SE = 0.019), CWD (0.034, SE = 0.012), and cougar predation (0.029, SE = 0.012). Marked elk killed by hunters and cougars typically were in good physical condition and not infected with CWD. Effects of mortality on population growth were exacerbated by low rates of pregnancy (subadults = 9.5%, SE = 6.6%; ad = 76.9%, SE = 4.2%) and perinatal survival (0.49, SE = 0.085 from 1 Feb to 1 Sep). Chronic wasting disease, increased predation, and reduced recruitment reduced the rate of increase for elk at WICA to approximately λ = 1.00 (SE = 0.027) during the past decade. Lower rates of increase are mitigating effects of elk on park vegetation, other wildlife, and neighboring lands and will facilitate population control, but may reduce opportunities for elk hunting outside the park. © 2011 The Wildlife Society  相似文献   

2.
    
ABSTRACT We assessed the potential for reestablishing elk (Cervus elaphus) in Great Smoky Mountains National Park (GSMNP), USA, by estimating vital rates of experimentally released animals from 2001 to 2006. Annual survival rates for calves ranged from 0.333 to 1.0 and averaged 0.592. Annual survival for subadult and adult elk (i.e., ≥ 1 yr of age) ranged from 0.690 to 0.933, depending on age and sex. We used those and other vital rates to model projected population growth and viability using a stochastic individual-based model. The annual growth rate (λ) of the modeled population over a 25-year period averaged 0.996 and declined from 1.059 the first year to 0.990 at year 25. The modeled population failed to attain a positive 25-year mean growth rate in 46.0% of the projections. Poor calf recruitment was an important determinant of low population growth. Predation by black bears (Ursus americanus) was the dominant calf mortality factor. Most of the variance of growth projections was due to demographic variation resulting from the small population size (n = 61). Management actions such as predator control may help increase calf recruitment, but our projections suggest that the GSMNP elk population may be at risk for some time because of high demographic variation.  相似文献   

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Abstract: Incomplete population counts indicate change in population sizes when constant proportionality holds, a condition that is rarely met. However, researchers have not explored whether constant proportionality holds for a segment of a population. I examined whether the female segment (juv, subadult M, subadult and ad F) of a Roosevelt elk (Cervus elaphus roosevelti) population displayed constant proportionality. When most food is in particular habitats, females of polygynous species should use that habitat frequently, even when food is limited, because they are more familiar with food distribution and abundance than males. I obtained counts of elk and tallies of naturally marked animals from vehicle surveys of a population inhabiting a landscape where forage was in meadows that were interspersed in closed-canopied forest. I conducted population surveys in January or February and estimated population size with Bowden's mark-resight estimator. Population size estimates declined from 130 in 1997 to 37 in 2006. The proportion of the population counted during surveys was inversely related to population size estimates. Estimated population sizes were inversely related to male (r2 = 0.56) but not female sighting probabilities (r2 = 0.004), which were ≥0.9. Constant proportionality in counts held for only the female segment of the population. Counts of the female segment of the population can inform managers about changes in this segment of the population over time.  相似文献   

4.
    
California, USA, is home to 3 subspecies of North American elk (Cervus canadensis): Roosevelt (C. c. roosevelti), Rocky Mountain (C. c. nelsoni), and tule (C. c. nannodes). Effective management requires a baseline understanding of each subspecies' range, admixture zones, and geographic patterns of genetic diversity. To address these questions, we genotyped 1,271 individual elk from California (n = 1,204) and reference populations of Rocky Mountain and Roosevelt elk from Nevada (n = 32) and Oregon (n = 35), USA. Using 19 polymorphic microsatellite loci, we detected admixture between Roosevelt and Rocky Mountain elk at a contact zone in northern California, and between Roosevelt and tule elk in north-coastal California and central-coastal California. We identified a genetically distinct population of Roosevelt elk in northwestern California, likely reflecting the remnant population that survived a large demographic decline from overhunting during the 1800s. Tule elk exhibited lower levels of heterozygosity (0.44 ± 0.03 [SD]) and allelic richness (2.9 ± 0.2) than Rocky Mountain (0.58 ± 0.05, 4.9 ± 0.4, respectively) and Roosevelt (0.50 ± 0.06, 4.4 ± 0.6, respectively) elk. Among tule elk populations, heterozygosity varied, with the lowest heterozygosity (0.23 ± 0.05) corresponding to the oldest enclosed herd used over the past century as a source of translocations. Among tule elk populations, genetic structure revealed several cases of successful and unsuccessful reintroduction or augmentation attempts. Results provide an essential baseline for future monitoring and decisions about harvest management, translocations to preserve genetic diversity, and landscape-level conservation planning to maintain, enhance, or obstruct connectivity of elk populations. Genome-wide sequencing and analyses are needed to quantify inbreeding absolutely and assess genetic load and the age of admixture where subspecies currently exchange genes.  相似文献   

5.
    
This study examined patterns of mortality and determinants of survival among elk recently restored to four sites in Ontario, Canada (1998–2005). We predicted that: (1) elk located in release sites closer to the core of their historic range would have higher survival; (2) survival would increase as an animal's time and experience on the landscape increased; and (3) survival rates would decline as animals moved farther away from the release site. During the study, 443 elk were radiocollared and released; 218 mortalities were documented. Predation by wolves was the most important proximate cause of mortality, followed by death due to injuries from translocation and/or capture myopathy, accidents, emaciation, poaching, and Parelaphostrongylus tenuis infection. Overall, annual survival of elk across Ontario ranged from 0.45 (0.37–0.53) to 0.81 (0.66–0.90), with rates being lowest in the years immediately following release and highest in the final years of the study; this pattern was due to high initial mortality from translocation injuries and/or capture myopathy and possibly lack of familiarity with novel habitat. Model‐averaged hazards further support this finding, as the most important factor influencing elk survival was the length of holding period, with elk released after limited holding being less likely to survive than those held for longer periods. Our results suggest that mortalities caused by capture myopathy and transportation‐related injuries are important sources of risk for translocated elk. The method of introduction to the novel landscape and behavior in the first year should be accommodated via soft‐release and appropriate release areas.  相似文献   

6.
    
We used an individual-based population model to perform a viability analysis to simulate population growth (λ) of 167 elk (Cervus elaphus manitobensis; 71 male and 96 female) released in the Cumberland Mountains, Tennessee, to estimate sustainability (i.e., λ > 1.0) and identify the most appropriate options for managing elk restoration. We transported elk from Elk Island National Park, Alberta, Canada, and from Land Between the Lakes, Kentucky, and reintroduced them beginning in December 2000 and ending in February 2003. We estimated annual survival rates for 156 radio-collared elk from December 2000 until November 2004. We used data from a nearby elk herd in Great Smoky Mountains National Park to simulate pessimistic and optimistic recruitment and performed population viability analyses to evaluate sustainability over a 25-year period. Annual survival averaged 0.799 (Total SE = 0.023). The primary identifiable sources of mortality were poaching, disease from meningeal worm (Parelaphostrongylus tenuis), and accidents (environmental causes and unintentional harvest). Population growth given pessimistic recruitment rates averaged 0.895 over 25 years (0.955 in year 1 to 0.880 in year 25); population growth was not sustainable in 100% of the runs. With the most optimistic estimates of recruitment, mean λ increased to 0.967 (1.038 in year 1 to 0.956 in year 25) with 99.6% of the runs failing to be sustainable. We suggest that further translocation efforts to increase herd size will be ineffective unless survival rates are increased in the Cumberland Mountains. © 2011 The Wildlife Society.  相似文献   

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Each spring, migratory herbivores around the world track or ‘surf’ green waves of newly emergent vegetation to distant summer or wet‐season ranges. This foraging tactic may help explain the great abundance of migratory herbivores on many seasonal landscapes. However, the underlying fitness benefits of this life‐history strategy remain poorly understood. A fundamental prediction of the green‐wave hypothesis is that migratory herbivores obtain fitness benefits from surfing waves of newly emergent vegetation more closely than their resident counterparts. Here we evaluate whether this behavior increases body‐fat levels – a critically important correlate of reproduction and survival for most ungulates – in elk Cervus elaphus of the Greater Yellowstone Ecosystem. Using satellite imagery and GPS tracking data, we found evidence that migrants (n = 23) indeed surfed the green wave, occupying sites 12.7 days closer to peak green‐up than residents (n = 16). Importantly, individual variation in surfing may help account for up to 6 kg of variation in autumn body‐fat levels. Our findings point to a pathway for anthropogenic changes to the green wave (e.g. climate change) or migrants’ ability to surf it (e.g. development) to impact migratory populations. To explore this possibility, we evaluated potential population‐level consequences of constrained surfing with a heuristic model. If green‐wave surfing deteriorates by 5–15 days from observed, our model predicts up to a 20% decrease in pregnancy rates, a 2.5% decrease in population growth, and a 30% decrease in abundance over 50 years. By linking green‐wave surfing to fitness and illustrating potential effects on population growth, our study provides new insights into the evolution of migratory behavior and the prospects for the persistence of migratory ungulate populations in a changing world.  相似文献   

8.
    
Previous research from 2001 to 2006 on an experimentally released elk (Cervus elaphus) population at Great Smoky Mountains National Park (GSMNP or Park) indicated that calf recruitment (i.e., calves reaching 1 yr of age per adult female elk) was low (0.306, total SE = 0.090) resulting in low or negative population growth (λ = 0.996, 95% CI = 0.945–1.047). Black bear (Ursus americanus) predation was the primary calf mortality factor. From 2006 to 2008, we trapped and relocated 49 bears (30 of which were radiocollared) from the primary calving areas in the Park and radiomonitored 67 (28 M:39 F) adult elk and 42 calves to compare vital rates and population growth with the earlier study. A model with annual calf recruitment rate correlating with the number of bears relocated each year was supported (ΔAICc = 0.000; β = 0.070, 95% CI = 0.028–0.112) and a model with annual calf recruitment differing from before to during bear relocation revealed an increase to 0.544 (total SE = 0.098; β = −1.092, 95% CI = −1.180 to −0.375). Using vital rates and estimates of process standard errors observed during our study, 25-yr simulations maintained a mean positive growth rate in 100% of the stochastic trials with λ averaging 1.118 (95% CI = 1.096–1.140), an increase compared with rates before bear relocation. A life table response experiment revealed that increases in population growth were mostly (67.1%) due to changes in calf recruitment. We speculate that behavioral adaptation of the elk since release also contributed to the observed increases in recruitment and population growth. Our results suggest that managers interested in elk reintroduction within bear range should consider bear relocation as a temporary means of increasing calf recruitment. © 2011 The Wildlife Society.  相似文献   

9.
    
ABSTRACT The status of recolonizing elk (Cervus elaphus) populations in Ontario, Canada, is unclear and there is a need for effective population survey methods that can be applied locally. We sought to develop a sightability model that could account for both low densities of elk and dense forest cover in elk-release areas in Ontario. We corrected winter aerial survey counts for sightability based on radiocollared animals known to be within observable distance of the aircraft. The multivariate model with the highest Akaike's Information Criterion corrected for sample size weight (wi = 0.427) revealed that elk group size, elk activity, dominant tree type, percent canopy cover, and percent conifer cover were significant predictors of elk sightability. The group-size effect indicated that odds of sighting an elk increased by 1.353 (95% CI = 0.874-3.689) for every additional elk. Standing elk were 5.033 (95% CI = 0.936-15.541) times more likely to be observed than were resting elk, and those located in conifer cover were 0.013 (95% CI = 0.001-0.278) times less likely to be sighted than elk in deciduous cover. Furthermore, elk located in >50% canopy cover and >50% conifer cover were 0.041 (95% CI = 0.003-0.619) times and 0.484 (95% CI = 0.024-9.721) times less likely to be sighted than elk in more open habitat, respectively. During model validation, observers detected 79% (113/143) of known elk in any given area, and population and sightability model predictions (±90% CI) overlapped with the population estimate, implying that our predictive model was robust. Unsurprisingly, large groups of elk in open habitat increased model precision, which highlights difficulties of counting Ontario elk in their northern range. We conclude that our model provided increased reliability for estimating elk numbers in Ontario compared to existing methods, and that the estimator may be useful in other areas where elk density is low and sightability is poor due to dense forest cover.  相似文献   

10.
    
The North Cascades (Nooksack) elk (Cervus elaphus) population declined during the 1980s, prompting a closure to state and tribal hunting in 1997 and an effort to restore the herd to former abundance. In 2005, we began a study to assess the size of the elk population, judge the effectiveness of restoration efforts, and develop a practical monitoring strategy. We concurrently evaluated 2 monitoring approaches: sightability correction modeling and mark-resight modeling. We collected data during February–April helicopter surveys and fit logistic regression models to predict the sightability of elk groups based on group and environmental variables. We used an information-theoretic criterion to compare 9 models of varying complexity; the best model predicted sightability of elk groups based on 1) transformed (log2) group size, 2) forest canopy cover (%), and 3) a categorical activity variable (active vs. bedded). The sightability model indicated relatively steady and modest herd growth during 2006–2011, but estimates were less than minimum-known-alive counts. We also used the logit-normal mixed effects (LNME) mark-resight model to generate estimates of total elk population size and the sizes of the adult female and branch-antlered male subpopulations. We explored 15 LNME models to predict total population size and 12 models to predict subpopulations. Our results indicated individual heterogeneity in resighting probabilities and variation in resighting probabilities across sexes and some years. Model-averaged estimates of total population size increased from 639 (95% CI = 570–706) in spring 2006 to 1,248 (95% CI = 1,094–1,401) in 2011. We estimated the adult female subpopulation increased from 381 (95% CI = 338–424) in spring 2006 to 573 (95% CI = 507–639) by 2011. The branch-antlered male subpopulation estimates increased from 87 (95% CI = 54–119) to 180 (95% CI = 118–241) from spring 2006 to spring 2011. The LNME model estimates were greater than sightability model estimates and minimum-known-alive counts. We concluded that mark-resight performed better and was a viable approach for monitoring this small elk population and possibly others with similar characteristics (i.e., small population and landscape scales), but this approach requires periodic marking of elk; we estimated mark-resight costs would be about 40% greater than sightability model application costs. The utility of sightability-correction modeling was limited by a high proportion of groups with low detectability on our densely forested landscape. © 2012 The Wildlife Society.  相似文献   

11.
    
We studied survival of elk (Cervus elaphus) ≥1 yr old and quantified mortality sources in the Blue Mountains of Washington, 2003–2006, following a period of extensive poaching. The population was managed under a spike-only general hunting season, with limited permits for larger males and for females. We radiomarked 190 elk (82 males and 39 females >1 yr old and 65 males 11 months old), most with rumen transmitters and neck radiocollars; 60 elk only received rumen transmitters. We estimated annual survival using known fate models and explored survival differences among sex and age classes and in 2 potentially different vulnerability zones for males. We found little support for differences in survival between younger (2–3-yr old) and older (≥4-yr old) branch-antlered males or zone differences for yearling males. A model with zone differences for branch-antlered males was the second ranked model and accounted for 14% of the available model weight. From the best-supported models, we estimated annual survival for yearling males at 0.41 (95% CI: 0.29–0.53). We estimated pooled adult female survival at 0.80 (95% CI: 0.64–0.93); when an age-class effect was included, point estimates were higher for prime-aged females (2–11 yr: S = 0.81 [0.70–0.88]) than for older females (≥12 yr: S = 0.72 [0.56–0.83]), but confidence intervals broadly overlapped. Only 1 of 7 models with a female age effect on survival was among the competitive models. For branch-antlered males, survival ranged 0.80–0.85, depending on whether zone variation was modeled. We recorded 78 deaths of radiomarked elk. Human-caused deaths (n = 55) predominated among causes and most were of yearling males killed during state-sanctioned hunts (n = 28). Most subadult male deaths were from tribal hunting (n = 5), and most mature males died from natural causes (n = 6) and tribal hunting (n = 5). We detected few illegal kills (n = 4). Our results suggest that increased enforcement effectively reduced poaching, that unreported tribal harvest was not a trivial source of mortality, and that spike-only general seasons were effective in recruiting branch-antlered males. © 2011 The Wildlife Society.  相似文献   

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In 2001 and 2002, 52 elk (Cervus canadensis; 21 males, 31 females), originally obtained from Elk Island National Park, Alberta, Canada, were transported and released into Cataloochee Valley in the northeastern portion of Great Smoky Mountains National Park (GRSM, Park), North Carolina, USA. The annual population growth rate (λ) was negative (0.996, 95% CI = 0.945–1.047) and predation by black bears (Ursus americanus) on elk calves was identified as an important determinant of population growth. From 2006 to 2008, 49 bears from the primary elk calving area (i.e., Cataloochee Valley) were trapped and translocated about 70 km to the southwestern portion of the Park just prior to elk calving. Per capita recruitment (i.e., the number of calves produced per adult female that survive to 1 year of age) increased from 0.306 prior to bear translocation (2001–2005) to 0.544 during years when bears were translocated (2006–2008) and λ increased to 1.118 (95% CI = 1.096–1.140). Our objective was to determine whether per capita calf recruitment rates after bear removal (2009–2019) at Cataloochee were similar to the higher rates estimated during bear removal (i.e., long-term response) or if they returned to rates before bear removal (i.e., short-term response), and how those rates compared with recruitment from portions of our study area where bears were not relocated. We documented 419 potential elk calving events and monitored 129 yearling and adult elk from 2001 to 2019. Known-fate models based on radio-telemetry and observational data supported calf recruitment returning to pre-2006 levels at Cataloochee (short-term response); recruitment of Cataloochee elk before and after bear relocation was lower (0.184) than during bear relocation (0.492). Recruitment rates of elk outside the removal area during the bear relocation period (0.478) were similar to before and after rates (0.420). In the Cataloochee Valley, cause-specific annual calf mortality rates due to predation by bears were 0.319 before, 0.120 during, and 0.306 after bear relocation. In contrast, the cause-specific annual mortality rate of calves in areas where bears were not relocated was 0.033 after the bear relocation period, with no bear predation on calves before or during bear relocation. The mean annual population growth rate for all monitored elk was 1.062 (95% CI = 0.979–1.140) after bear relocation based on the recruitment and survival data. Even though the effects of bear removal were temporary, the relocations were effective in achieving a short-term increase in elk recruitment, which was important for the reintroduction program given that the elk population was small and vulnerable to extirpation.  相似文献   

13.
    
Abstract: The realized impact of a vital rate on population growth (λ) is determined by both the relative influence of the vital rate on λ (elasticity) and its magnitude of variability. We estimated mean survival and reproductive rates in elk (Cervus elaphus) and spatial and temporal variation in these rates from 37 sources located primarily across the Rocky Mountain region and northwestern United States. We removed sampling variance from estimates of process variance both within and across vital-rate data sets using the variance discounting method developed by White (2000). Deterministic elasticities calculated from a population matrix model parameterized with these mean vital rates ranked adult female survival (eScow = 0.869) much higher than calf survival (eScalf = 0.131). However, process variance in calf survival was >11 times greater than process variance in female survival across data sets and 10 times greater on average within studies. We conducted Life-Stage Simulation Analysis to incorporate both vital-rate elasticity patterns and empirical estimates of variability to identify those vital rates most influential in elk population dynamics. The overwhelming magnitude of variation in calf survival explained 75% of the variation in the population growth rates generated from 1,000 matrix replicates, compared to just 16% of the variation in λ explained by variation in female survival. Variation in calf survival greatly impacts elk population growth and calls into question the utility of classical elasticity analysis alone for guiding elk management. These results also suggest that the majority of interannual variability that wildlife managers document in late-winter and spring elk surveys is attributable to variation in calf survival over the previous year and less influenced by variation in the harvest of females during the preceding autumn. To meet elk population size objectives, managers should consider the inherent variation in calf survival, and its apparent sensitivity to management, in addition to female harvest.  相似文献   

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Abstract: Age ratios (e.g., calf:cow for elk and fawn:doe for deer) are used regularly to monitor ungulate populations. However, it remains unclear what inferences are appropriate from this index because multiple vital rate changes can influence the observed ratio. We used modeling based on elk (Cervus elaphus) life-history to evaluate both how age ratios are influenced by stage-specific fecundity and survival and how well age ratios track population dynamics. Although all vital rates have the potential to influence calf:adult female ratios (i.e., calf:cow ratios), calf survival explained the vast majority of variation in calf:adult female ratios due to its temporal variation compared to other vital rates. Calf:adult female ratios were positively correlated with population growth rate (Λ) and often successfully indicated population trajectories. However, calf:adult female ratios performed poorly at detecting imposed declines in calf survival, suggesting that only the most severe declines would be rapidly detected. Our analyses clarify that managers can use accurate, unbiased age ratios to monitor arguably the most important components contributing to sustainable ungulate populations, survival rate of young and Λ. However, age ratios are not useful for detecting gradual declines in survival of young or making inferences about fecundity or adult survival in ungulate populations. Therefore, age ratios coupled with independent estimates of population growth or population size are necessary to monitor ungulate population demography and dynamics closely through time.  相似文献   

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Depending on the habitats they live in, temperate ungulates have adapted to different degrees to seasonally changing forage and weather conditions, and to specific escape strategies from predators. Alpine chamois, a mountain ungulate, and red deer, originally adapted to open plains, would therefore be expected to differ in their physiological responses to potential stressors. Based on 742 chamois and 1557 red deer fecal samples collected year‐round every 2 weeks for 4 years at the same locations within a strictly protected area in the Swiss Alps, we analyzed glucocorticoid metabolite (FGM) concentrations for both species. Results from linear mixed effects models revealed no physiological stress response to changing visitor numbers, but instead to drought conditions for both species during summer. In winter, FGM concentrations increased with increasing snow height in both species, but this response was modulated by temperature in red deer. Chamois showed a stronger stress response to increasing snow height during November and December than between January and March, while FGM concentrations increased with decreasing temperature throughout winter. An increase in FGM concentrations with decreasing forage digestibility during winter was found only for red deer. The results are thus partly in contradiction to expectations based on feeding type and adaptations to different habitats between the two species. The lack of a response to forage digestibility in chamois may reflect either better adaptation to difficult feeding conditions in subalpine forests, or, by contrast, strong constraints imposed by forage quality. The similar responses of both species to weather conditions in winter suggest that climatic factors at the elevations examined here are sufficiently harsh to be limiting to temperate ungulates regardless of their specific adaptations to this environment.  相似文献   

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ABSTRACT We analyzed counts of northern Yellowstone elk (Cervus elaphus) in Yellowstone National Park, Wyoming, USA, over 70 years to evaluate the effects of changing management on population trends. Population reduction efforts and hunter harvests during 1932–1968 removed 71,330 elk and decreased estimated abundance from 16,000 to 6,000 elk. Abundance increased to approximately 17,000 elk (λ = 1.19) when removals ceased and harvests were very small during 1969–1975. Moderate to liberal hunter harvests of antlerless elk outside the Park during 1976–2004 removed a relatively consistent proportion (26 ± 0.1 [SD]%) of females that migrated outside the park, mostly from prime-age (3–15 yr) classes with high reproductive value. Substantial winterkill was infrequent (1989, 1997), but it significantly reduced calf survival when it occurred. Wolves (Canis lupus) were reintroduced in 1995–1996 and rapidly increased in abundance (λ = 1.23) and distribution. Estimated wolf kill of elk now exceeds hunter harvest, but has a smaller effect on population dynamics because wolves concentrate on calves and older females (>14 yr) with low reproductive value. During 1995–2004, estimated abundance decreased from 23,000 to 12,000 elk. The recent ratio of wolves to elk is relatively low compared to the estimated equilibrium ratio, suggesting that the wolf population may yet increase in the future. Thus, reduction of harvests of prime-aged female elk to decrease removals of animals with high reproductive value and increase adult female survival appears essential. We analyzed the relative impact of removals by hunters and by wolves using Fisher's (1930) reproductive value and found that the impact of hunters is far more important than that by wolves, a finding of broad significance.  相似文献   

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ABSTRACT We evaluated survival of elk (Cervus elaphus) calves on 2 contrasting study areas in north-central Idaho, USA, from 1997 to 2004. Recruitment was modest (>30 calves:100 F [calves of either sex: F elk 1 yr old]) and stable on the South Fork study area and low (<20 calves:100 F) and declining on the Lochsa study area. The primary proximate cause of calf mortality on both study areas was predation by black bears (Ursus americanus) and mountain lions (Puma concolor). We experimentally manipulated populations of black bears and mountain lions on a portion of each study area. Black bear harvest (harvest density/600km2) initially doubled on the Lochsa treatment after manipulating season bag limits. Mountain lion harvest also increased by 60% but varied widely during the manipulation period. Harvest seasons were closed for black bears and mountain lions on the treatment portion of the South Fork study area. Using the Andersen—Gill formulation (A-G) of the Cox proportional hazards model, we examined effects of landscape structure, predator harvest levels, and biological factors on summer calf survival. We used Akaike's Information Criterion (AICc) and multimodel inference to assess some potentially useful predictive factors relative to calf survival. We generated risk ratios for both the best models and for model-averaged coefficients. Our models predicted that calf survival was influenced by biological factors, landscape surrounding calf locations, and predator harvest levels. The model that best explained mortality risk to calves on the Lochsa included black bear harvest (harvest density/600 km2), estimated birth mass of calves, and percentage of shrub cover surrounding calf locations. Incorporating a shrub X time interaction allowed us to correct for nonproportionality and detect that effect of shrub cover was only influential during the first 14 days of a calf's life. Model-averaging indicated that estimated birth mass of calves and black bear harvest were twice as important as the next variables, but age of calves at capture was also influential in calf survival. The model that best explained mortality risk to calves on the South Fork included black bear harvest, age of calves at capture, and gender of calves. Model-averaging indicated that age at capture and black bear harvest were twice as important as the next variable, forest with 33–66% canopy cover (Canopy 33–66). Risk to calves decreased when calves occupied areas with more of this forest cover type. Model-averaging also indicated that increased mountain lion harvest lowered calf mortality risk 4% for every 1-unit increase in lion harvest (harvest density/600 km2) but was lower (<25%) in importance compared to age at capture and black bear harvest. Our results suggest that levels of predator harvest, and presumably predator density, resource limitations expressed through calf birth mass, and habitat structure had substantial effects on calf survival. Our results can be generalized to other areas where managers are dealing with low calf elk recruitment. However, because factors vary spatially, a single management strategy applied in different areas will probably not have the same effect on calf survival.  相似文献   

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