Brown Bear Density and Estimated Harvest Rates in Northwestern Alaska

Human-caused mortality in general, and unregulated hunting in particular, have been implicated in reductions in brown bear (Ursus arctos) populations throughout much of their range. In northwestern Alaska, USA, bear densities have not been assessed in 20 years while harvest regulations have been liberalized, raising concerns that broad undetected population declines might occur. We used a modified mark-resight approach to estimate brown bear density during 2005–2018 in 4 subareas throughout the region. We also summarized harvest information for each subarea and used our survey results to estimate harvest rates. We estimated densities for independent bears assuming constant or heterogeneous probabilities of detection and occurrence. We present the results of the constant model for more direct comparison with past work and the heterogeneity model results to provide estimates of density that are less likely to be negatively biased. Using the constant model, we estimated the density of independent bears was 17.0, 49.2, 24.9, and 19.4/1,000 km² on portions of the Seward Peninsula, the lower Noatak River, the upper Noatak River, and Gates of the Arctic National Park and Preserve, respectively. These estimates are broadly similar to those from past work in interior and northwestern Alaska, with the exception of the lower Noatak River subarea where our estimates are the highest reported for a bear population in northern Alaska. We estimated that the harvest rate on the Seward Peninsula was approximately 5.2% or 7.7% on average, depending upon the model used. In the remaining areas, we estimated annual harvest rates were <2.5%, well within sustainability guidelines from past work. Overall, our results suggest that brown bear densities are similar or somewhat higher than in the past in much of northwestern Alaska and that current harvest rates are sustainable in most areas, except perhaps the Seward Peninsula. Ongoing survey work will be useful for further evaluating the assumptions of the modified mark-resight survey approach, assessing population trajectory, and determining the effect of harvest on brown bear populations. © 2021 The Wildlife Society.     

Inter-Population Movements of Steller Sea Lions in Alaska with Implications for Population Separation

Genetic studies and differing population trends support the separation of Steller sea lions (Eumetopias jubatus) into a western distinct population segment (WDPS) and an eastern DPS (EDPS) with the dividing line between populations at 144° W. Despite little exchange for thousands of years, the gap between the breeding ranges narrowed during the past 15–30 years with the formation of new rookeries near the DPS boundary. We analyzed >22,000 sightings of 4,172 sea lions branded as pups in each DPS from 2000–2010 to estimate probabilities of a sea lion born in one DPS being seen within the range of the other DPS (either ‘West’ or ‘East’). Males from both populations regularly traveled across the DPS boundary; probabilities were highest at ages 2–5 and for males born in Prince William Sound and southern Southeast Alaska. The probability of WDPS females being in the East at age 5 was 0.067 but 0 for EDPS females which rarely traveled to the West. Prince William Sound-born females had high probabilities of being in the East during breeding and non-breeding seasons. We present strong evidence that WDPS females have permanently emigrated to the East, reproducing at two ‘mixing zone’ rookeries. We documented breeding bulls that traveled >6,500 km round trip from their natal rookery in southern Alaska to the northern Bering Sea and central Aleutian Islands and back within one year. WDPS animals began moving East in the 1990s, following steep population declines in the central Gulf of Alaska. Results of our study, and others documenting high survival and rapid population growth in northern Southeast Alaska suggest that conditions in this mixing zone region have been optimal for sea lions. It is unclear whether eastward movement across the DPS boundary is due to less-optimal conditions in the West or a reflection of favorable conditions in the East.     

Effective size of harvested ungulate populations

The harvest of ungulate populations is often directed against certain sex or age classes to maximize the yield in terms of biomass, number of shot animals or number of trophies. Here we examine how such directional harvest affects the effective size of the population. We parameterize an age-specific model assumed to describe the dynamics of Fennoscandian moose. Based on expressions for the demographic variance     for a small subpopulation of heterozygotes Aa bearing a rare neutral allele a , we use this model to calculate how different harvest strategies influence the effective size of the population, given that the population remains stable after harvest. We show that the annual genetic drift, determined by     , increases with decreasing harvest rate of calves and increasing sex bias in the harvest towards bulls 1 year or older. The effective population size per generation decreased with reduced harvest of calves and increased harvest of bulls 1 year or older. The magnitude of these effects depends on the age-specific pattern of variation in reproductive success, which influences the demographic variance. This shows that the choice of harvest strategy strongly affects the genetic dynamics of harvested ungulate populations.     

Meta-Analysis of Relationships between Human Offtake,Total Mortality and Population Dynamics of Gray Wolves (Canis lupus)

Following the growth and geographic expansion of wolf (Canis lupus) populations reintroduced to Yellowstone National Park and central Idaho in 1995–1996, Rocky Mountain wolves were removed from the endangered species list in May 2009. Idaho and Montana immediately established hunting seasons with quotas equaling 20% of the regional wolf population. Combining hunting with predator control, 37.1% of Montana and Idaho wolves were killed in the year of delisting. Hunting and predator control are well-established methods to broaden societal acceptance of large carnivores, but it is unprecedented for a species to move so rapidly from protection under the Endangered Species Act to heavy direct harvest, and it is important to use all available data to assess the likely consequences of these changes in policy. For wolves, it is widely argued that human offtake has little effect on total mortality rates, so that a harvest of 28–50% per year can be sustained. Using previously published data from 21 North American wolf populations, we related total annual mortality and population growth to annual human offtake. Contrary to current conventional wisdom, there was a strong association between human offtake and total mortality rates across North American wolf populations. Human offtake was associated with a strongly additive or super-additive increase in total mortality. Population growth declined as human offtake increased, even at low rates of offtake. Finally, wolf populations declined with harvests substantially lower than the thresholds identified in current state and federal policies. These results should help to inform management of Rocky Mountain wolves.     

Inferences About Ungulate Population Dynamics Derived From Age Ratios

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.     

Size specific predation by herons and its effect on the sex-ratio of natural populations of the mosquito fish Gambusia affinis baird and girard

Summary Sex-ratios of Gambusia affinis populations in freshwater marshes in the Camargue (Rhône Delta), are highly biased in favour of males, whereas the sex-ratios in ditches are close to unity. Studies of the diet of free living birds and experimental studies on prey size selection in captivity show that the abnormal sex-ratios in marshes can be attributed to differential heron predation. Ditches are relatively free from predation. Mature female Gambusia are larger, and have an energy content 5–25 times greater than that of mature males. Handling times of Grey Heron (Ardea cinerea) and Little Egret (Egretta garzetta) are only slightly longer for female Gambusia than males. Hence, females represent a much more profitable prey.Analysis of nestling regurgitates show that Gambusia makes up a considerable proportion of the diet of four species of Camargue herons, and that the majority of Gambusia taken are females. Under experimental conditions, captive herons consume almost exclusively female fish, even when offered in ratios where they are heavily outnumbered by males.The relevance of these results to optimal diet theory is discussed.     

Characteristics of foraging sites and protein status in wintering muskoxen: insights from isotopes of nitrogen

Identifying links between nutritional condition of individuals and population trajectories greatly enhances our understanding of the ecology, conservation, and management of wildlife. For northern ungulates, the potential impacts of a changing climate to populations are predicted to be nutritionally mediated through an increase in the severity and variance in winter conditions. Foraging conditions and the availability of body protein as a store for reproduction in late winter may constrain productivity in northern ungulates, yet the link between characteristics of wintering habitats and protein status has not been established for a wild ungulate. We used a non‐invasive proxy of protein status derived from isotopes of N in excreta to evaluate the influence of winter habitats on the protein status of muskoxen in three populations in Alaska (2005–2008). Multiple regression and an information‐theoretic approach were used to compare models that evaluated the influence of population, year, and characteristics of foraging sites (components of diet and physiography) on protein status for groups of muskoxen. The observed variance in protein status among groups of muskoxen across populations and years was partially explained (45%) by local foraging conditions that affected forage availability. Protein status improved for groups of muskoxen as the amount of graminoids in the diet increased (?0.430 ± 0.31, β± 95% CI) and elevation of foraging sites decreased (0.824 ± 0.67). Resources available for reproduction in muskoxen are highly dependent upon demographic, environmental, and physiographic constraints that affect forage availability in winter. Due to their very sedentary nature in winter, muskoxen are highly susceptible to localized foraging conditions; therefore, the spatial variance in resource availability may exert a strong effect on productivity. Consequently, there is a clear need to account for climate–topography effects in winter at multiple scales when predicting the potential impacts of climatic shifts on population trajectories of muskoxen.     

Effect of Harvest on a Brown Bear Population in Alaska

There is a long and contentious history of brown bear (Ursus arctos) harvest management in Alaska, USA, the state that hosts the largest brown bear population in North America. In the mid-1990s, the Alaska Board of Game set the population objective for brown bears in Game Management Unit 13 A, located in interior southcentral Alaska, to be reduced by 50% to improve survival of moose (Alces alces) calves. The Board began further liberalizing brown bear harvest regulations for the unit beginning in regulatory year 1995, though adult females and their dependent offspring (i.e., cubs <2 yrs old) were protected. To evaluate progress toward this abundance objective, we captured and collared bears between 2006 and 2011 and conducted a capture-mark-resight density survey during summer 2011 for comparison to a similar baseline survey conducted in 1998. We report the results of the density survey and vital rates estimated from resight histories of collared bears and harvest information spanning from 1985 (10 years before establishment of the population objective) to 2012. There was a 25–40% reduction in abundance between 1998 and 2011. Population growth rates derived from density estimates and a matrix population projection model indicated that the population declined by 2.3–4.2% annually. We estimated harvest rates to be 8–15% annually, but harvest composition data indicated no changes in skull size, age distribution, or overall sex ratio. There was evidence of an increase in the proportion of older females in the harvest. Demographic analysis indicated high reproductive output and recruitment, potentially indicating a density-dependent compensatory response to reduced population size. Despite 13 years of harvest rates in excess of what had previously been considered to be sustainable for this population, the objective of reducing bear abundance by 50% had not been achieved as of 2011. The protection of females and dependent offspring in our study population appears to be a sufficient safeguard against a precipitous population decline while still permitting progress toward the population objective through high harvest on other segments of the population. © 2020 The Wildlife Society.     

Ecosystem Scale Declines in Elk Recruitment and Population Growth with Wolf Colonization: A Before-After-Control-Impact Approach

The reintroduction of wolves (Canis lupus) to Yellowstone provided the unusual opportunity for a quasi-experimental test of the effects of wolf predation on their primary prey (elk – Cervus elaphus) in a system where top-down, bottom-up, and abiotic forces on prey population dynamics were closely and consistently monitored before and after reintroduction. Here, we examined data from 33 years for 12 elk population segments spread across southwestern Montana and northwestern Wyoming in a large scale before-after-control-impact analysis of the effects of wolves on elk recruitment and population dynamics. Recruitment, as measured by the midwinter juvenile∶female ratio, was a strong determinant of elk dynamics, and declined by 35% in elk herds colonized by wolves as annual population growth shifted from increasing to decreasing. Negative effects of population density and winter severity on recruitment, long recognized as important for elk dynamics, were detected in uncolonized elk herds and in wolf-colonized elk herds prior to wolf colonization, but not after wolf colonization. Growing season precipitation and harvest had no detectable effect on recruitment in either wolf treatment or colonization period, although harvest rates of juveniles∶females declined by 37% in wolf-colonized herds. Even if it is assumed that mortality due to predation is completely additive, liberal estimates of wolf predation rates on juvenile elk could explain no more than 52% of the total decline in juvenile∶female ratios in wolf-colonized herds, after accounting for the effects of other limiting factors. Collectively, these long-term, large-scale patterns align well with prior studies that have reported substantial decrease in elk numbers immediately after wolf recolonization, relatively weak additive effects of direct wolf predation on elk survival, and decreased reproduction and recruitment with exposure to predation risk from wolves.     

Changes in Size and Age of Chinook Salmon Oncorhynchus tshawytscha Returning to Alaska

The average sizes of Pacific salmon have declined in some areas in the Northeast Pacific over the past few decades, but the extent and geographic distribution of these declines in Alaska is uncertain. Here, we used regression analyses to quantify decadal trends in length and age at maturity in ten datasets from commercial harvests, weirs, and spawner abundance surveys of Chinook salmon Oncorhynchus tshawytscha throughout Alaska. We found that on average these fish have become smaller over the past 30 years (~6 generations), because of a decline in the predominant age at maturity and because of a decrease in age-specific length. The proportion of older and larger 4-ocean age fish in the population declined significantly (P < 0.05) in all stocks examined by return year or brood year. Our analyses also indicated that the age-specific lengths of 4-ocean fish (9 of 10 stocks) and of 3-ocean fish (5 of 10 stocks) have declined significantly (P < 0.05). Size-selective harvest may be driving earlier maturation and declines in size, but the evidence is not conclusive, and additional factors, such as ocean conditions or competitive interactions with other species of salmon, may also be responsible. Regardless of the cause, these wide-spread phenotypic shifts influence fecundity and population abundance, and ultimately may put populations and associated fisheries at risk of decline.     

High Natality Rates of Endangered Steller Sea Lions in Kenai Fjords,Alaska and Perceptions of Population Status in the Gulf of Alaska

Steller sea lions experienced a dramatic population collapse of more than 80% in the late 1970s through the 1990s across their western range in Alaska. One of several competing hypotheses about the cause holds that reduced female reproductive rates (natality) substantively contributed to the decline and continue to limit recovery in the Gulf of Alaska despite the fact that there have been very few attempts to directly measure natality in this species. We conducted a longitudinal study of natality among individual Steller sea lions (n = 151) at a rookery and nearby haulouts in Kenai Fjords, Gulf of Alaska during 2003–2009. Multi-state models were built and tested in Program MARK to estimate survival, resighting, and state transition probabilities dependent on whether or not a female gave birth in the previous year. The models that most closely fit the data suggested that females which gave birth had a higher probability of surviving and giving birth in the following year compared to females that did not give birth, indicating some females are more fit than others. Natality, estimated at 69%, was similar to natality for Steller sea lions in the Gulf of Alaska prior to their decline (67%) and much greater than the published estimate for the 2000s (43%) which was hypothesized from an inferential population dynamic model. Reasons for the disparity are discussed, and could be resolved by additional longitudinal estimates of natality at this and other rookeries over changing ocean climate regimes. Such estimates would provide an appropriate assessment of a key parameter of population dynamics in this endangered species which has heretofore been lacking. Without support for depressed natality as the explanation for a lack of recovery of Steller sea lions in the Gulf of Alaska, alternative hypotheses must be more seriously considered.     

Demographic responses to climate change in a threatened Arctic species

The Arctic is undergoing rapid and accelerating change in response to global warming, altering biodiversity patterns, and ecosystem function across the region. For Arctic endemic species, our understanding of the consequences of such change remains limited. Spectacled eiders (Somateria fischeri), a large Arctic sea duck, use remote regions in the Bering Sea, Arctic Russia, and Alaska throughout the annual cycle making it difficult to conduct comprehensive surveys or demographic studies. Listed as Threatened under the U.S. Endangered Species Act, understanding the species response to climate change is critical for effective conservation policy and planning. Here, we developed an integrated population model to describe spectacled eider population dynamics using capture–mark–recapture, breeding population survey, nest survey, and environmental data collected between 1992 and 2014. Our intent was to estimate abundance, population growth, and demographic rates, and quantify how changes in the environment influenced population dynamics. Abundance of spectacled eiders breeding in western Alaska has increased since listing in 1993 and responded more strongly to annual variation in first‐year survival than adult survival or productivity. We found both adult survival and nest success were highest in years following intermediate sea ice conditions during the wintering period, and both demographic rates declined when sea ice conditions were above or below average. In recent years, sea ice extent has reached new record lows and has remained below average throughout the winter for multiple years in a row. Sea ice persistence is expected to further decline in the Bering Sea. Our results indicate spectacled eiders may be vulnerable to climate change and the increasingly variable sea ice conditions throughout their wintering range with potentially deleterious effects on population dynamics. Importantly, we identified that different demographic rates responded similarly to changes in sea ice conditions, emphasizing the need for integrated analyses to understand population dynamics.     

Malignant Lymphatic and Hematopoietic Neoplasms Mortality in Serbia, 1991–2010: A Joinpoint Regression Analysis

Background

Limited data on mortality from malignant lymphatic and hematopoietic neoplasms have been published for Serbia.

Methods

The study covered population of Serbia during the 1991–2010 period. Mortality trends were assessed using the joinpoint regression analysis.

Results

Trend for overall death rates from malignant lymphoid and haematopoietic neoplasms significantly decreased: by −2.16% per year from 1991 through 1998, and then significantly increased by +2.20% per year for the 1998–2010 period. The growth during the entire period was on average +0.8% per year (95% CI 0.3 to 1.3). Mortality was higher among males than among females in all age groups. According to the comparability test, mortality trends from malignant lymphoid and haematopoietic neoplasms in men and women were parallel (final selected model failed to reject parallelism, P = 0.232). Among younger Serbian population (0–44 years old) in both sexes: trends significantly declined in males for the entire period, while in females 15–44 years of age mortality rates significantly declined only from 2003 onwards. Mortality trend significantly increased in elderly in both genders (by +1.7% in males and +1.5% in females in the 60–69 age group, and +3.8% in males and +3.6% in females in the 70+ age group). According to the comparability test, mortality trend for Hodgkin''s lymphoma differed significantly from mortality trends for all other types of malignant lymphoid and haematopoietic neoplasms (P<0.05).

Conclusion

Unfavourable mortality trend in Serbia requires targeted intervention for risk factors control, early diagnosis and modern therapy.     

Using Health Surveillance Systems Data to Assess the Impact of AIDS and Antiretroviral Treatment on Adult Morbidity and Mortality in Botswana

Introduction

Botswana''s AIDS response included free antiretroviral treatment (ART) since 2002, achieving 80% coverage of persons with CD4<350 cells/µl by 2009–10. We explored impact on mortality and HIV prevalence, analyzing surveillance and civil registration data.

Methods

Hospital natural cause admissions and deaths from the Health Statistics Unit (HSU) over 1990–2009, all-cause deaths from Midnight Bed Census (MNC) over 1990–2011, institutional and non-institutional deaths recorded in the Registry of Birth and Deaths (RBD) over 2003–2010, and antenatal sentinel surveillance (ANC) over 1992–2011 were compared to numbers of persons receiving ART. Mortality was adjusted for differential coverage and completeness of institutional and non-institutional deaths, and compared to WHO and UNAIDS Spectrum projections.

Results

HSU deaths per 1000 admissions declined 49% in adults 15–64 years over 2003–2009. RBD mortality declined 44% (807 to 452/100,000 population in adults 15–64 years) over 2003–2010, similarly in males and females. Generally, death rates were higher in males; declines were greater and earlier in younger adults, and in females. In contrast, death rates in adults 65+, particularly females increased over 2003–2006. MNC all-age post-neonatal mortality declined 46% and 63% in primary and secondary level hospitals, over 2003–2011. We estimated RBD captured 80% of adult deaths over 2006–2011. Comparing empirical, completeness-adjusted deaths to Spectrum estimates, declines over 2003–2009 were similar overall (47% vs. 54%); however, Spectrum projected larger and earlier declines particularly in women. Following stabilization and modest decreases over 1998–2002, HIV prevalence in pregnant women 15–24 and 25–29-years declined by >50% and >30% through 2011, while continuing to increase in older women.

Conclusions

Adult mortality in Botswana fell markedly as ART coverage increased. HIV prevalence declines may reflect ART-associated reductions in sexual transmission. Triangulation of surveillance system data offers a reasonable approach to evaluate impact of HIV/AIDS interventions, complementing cohort approaches that monitor individual-level health outcomes.     

Weather conditions during hunting season affect the number of harvested roe deer (Capreolus capreolus)

Due to human‐induced climate and landscape changes, distribution and abundance of many ungulate species have increased worldwide. Especially in areas where natural predators are absent, hunting is the essential management tool for regulating ungulate populations. Therefore, understanding the factors associated with harvest rates is the first step toward an adaptive management approach. Weather influences hunter and ungulate behavior and thus presumably harvest, but how and which meteorological parameters are linked to harvest numbers have rarely been evaluated. We used nearly 65,000 “sit and wait” and driven hunt harvests of roe deer (Capreolus capreolus) in Bavaria, Germany, and weather data from 2008 to 2017 to test for factors affecting roe deer harvests (i.e., temperature, rain hours, wind speed, sunshine duration, snow depth, workdays vs. weekends, month) using zero‐inflated negative binomial mixed‐effect models. Our results reveal that, besides workdays, high temperatures and prolonged rain resulted in fewer harvested animals, whereas sunshine duration in summer and snow height in snow‐rich areas partially favored harvests during sitting hunts in summer and winter, respectively. The influence of wind speed varied over the course of the year. In summer and autumn, wind speed commonly had a negative effect, positively affecting harvests in winter in some regions. Daily harvest numbers decreased during the summer and autumn hunting periods (May till mid‐October), while they increased during the winter period (mid‐October till mid‐January). Interestingly, harvest success during driven hunts, which are planned well in advance and therefore take place largely independent of weather conditions, was similarly affected by the weather. This result suggests that the inferred weather influence is not only due to the hunters'' decisions but also due to deer behavior. Since many ungulate populations may further benefit from climate change, building an understanding of the relationship between hunting success and weather will aid adaptive ungulate management.     

Dynamics of an Infectious Keratoconjunctivitis Outbreak by Mycoplasma conjunctivae on Pyrenean Chamois Rupicapra p. pyrenaica

Between 2006 and 2008, an outbreak of Infectious Keratoconjunctivitis (IKC) affected Pyrenean chamois Rupicapra p. pyrenaica, an endemic subspecies of mountain ungulate that lives in the Pyrenees. The study focused on 14 mountain massifs (180,000 ha) where the species’ population is stable. Cases of IKC were detected in ten of the massifs and, in five of them, mortality was substantial. The outbreak spread quickly from the first location detected, with two peaks in mortality that affected one (2007) and three (2008) massifs. In the latter, the peak was seasonal (spring to autumn) and, in the former, the outbreak persisted through winter. To identify the outbreak’s aetiology, we examined 105 Pyrenean chamois clinically affected with IKC. TaqMan rt-PCR identified Mycoplasma conjunctivae in 93 (88.5%) of the chamois. Another rt-PCR detected Chlamydophila spp. in 14 of chamois, and 12 of those had mixed infections with mycoplasmas. In the period 2000–2007, the chamois population increased slightly (λ 1.026) but decreased significantly during the IKC outbreak (λ 0.8, 2007–2008; λ 0.85, 2008–2009) before increasing significantly after the outbreak (λ 1.1, 2009–2010). Sex-biased mortality shifted the adult sex ratio toward males (from 0.6 to 0.7 males per female) and reduced productivity slightly. Hunting was practically banned in the massifs where chamois experienced significant mortality and allowed again after the outbreak ended. Long-term monitoring of wild populations provides a basis for understanding the impacts of disease outbreaks and improves management decisions, particularly when species are subject to extractive exploitation.     

Long-term responses in arctic ungulate dynamics to changes in climatic and trophic processes

 Following predictions from climatic general circulation models, the effects of perturbations in global climate are expected to be most pronounced in the Northern Hemisphere. Elaborating on a recently developed plant–herbivore–climate model, we explore statistically how different winter climate regimes and density-dependent processes during the past century have affected population dynamics of two arctic ungulate species. Our analyses were performed on the dynamics of six muskox and six caribou populations. In muskoxen, variation in winter climate, mediated through the North Atlantic Oscillation (NAO), explained up to 24% of the variation in interannual abundance, whereas in caribou up to 16% was explained by the NAO. Muskoxen responded negatively following warm and snowy winters, whereas caribou responded negatively to dry winters. Direct and delayed density dependence was recorded in most populations and explained up to 32% and 90% of variations in abundance of muskoxen and caribou, respectively. Received: November 19, 2001 / Accepted: May 28, 2002     

Patterns and causes of demographic variation in a harvested moose population: evidence for the effects of climate and density-dependent drivers

1.?Better understanding of the mechanisms affecting demographic variation in ungulate populations is needed to support sustainable management of harvested populations. While studies of moose Alces alces L. populations have previously explored temporal variation in demographic processes, managers responsible for populations that span large heterogeneous landscapes would benefit from an understanding of how demography varies across biogeographical gradients in climate and other population drivers. Evidence of thresholds in population response to manageable and un-manageable drivers could aid resource managers in identifying limits to the magnitude of sustainable change. 2.?Generalized additive models (GAMs) were used to evaluate the relative importance of population density, habitat abundance, summer and winter climatic conditions, primary production, and harvest intensity in explaining spatial variation in moose vital rates in Ontario, Canada. Tree regression was used to test for thresholds in the magnitudes of environmental predictor variables that significantly affected population vital rates. 3.?Moose population growth rate was negatively related to moose density and positively related to the abundance of mixed deciduous habitat abundant in forage. Calf recruitment was negatively related to a later start of the growing season and calf harvest. The ratio of bulls to cows was related to male harvest and hunter access, and thresholds were evident in predictor variables for all vital rate models. 4.?Findings indicate that the contributions of density-dependent and independent factors can vary depending on the scale of population process. The importance of density dependence and habitat supply to low-density ungulate populations was evident, and management strategies for ungulates may be improved by explicitly linking forest management and harvest. Findings emphasize the importance of considering summer climatic influences to ungulate populations, as recruitment in moose was more sensitive to the timing of vegetation green-up than winter severity. The efficacy of management decisions for harvested ungulates may require regional shifts in targets where populations span bioclimatic gradients. The use of GAMs in combination with recursive partitioning was demonstrated to be an informative analytical framework that captured nonlinear relationships common in natural processes and thresholds that are relevant to population management in diverse systems.     

A Comparison of Grizzly Bear Demographic Parameters Estimated from Non-Spatial and Spatial Open Population Capture-Recapture Models

Capture-recapture studies are frequently used to monitor the status and trends of wildlife populations. Detection histories from individual animals are used to estimate probability of detection and abundance or density. The accuracy of abundance and density estimates depends on the ability to model factors affecting detection probability. Non-spatial capture-recapture models have recently evolved into spatial capture-recapture models that directly include the effect of distances between an animal’s home range centre and trap locations on detection probability. Most studies comparing non-spatial and spatial capture-recapture biases focussed on single year models and no studies have compared the accuracy of demographic parameter estimates from open population models. We applied open population non-spatial and spatial capture-recapture models to three years of grizzly bear DNA-based data from Banff National Park and simulated data sets. The two models produced similar estimates of grizzly bear apparent survival, per capita recruitment, and population growth rates but the spatial capture-recapture models had better fit. Simulations showed that spatial capture-recapture models produced more accurate parameter estimates with better credible interval coverage than non-spatial capture-recapture models. Non-spatial capture-recapture models produced negatively biased estimates of apparent survival and positively biased estimates of per capita recruitment. The spatial capture-recapture grizzly bear population growth rates and 95% highest posterior density averaged across the three years were 0.925 (0.786–1.071) for females, 0.844 (0.703–0.975) for males, and 0.882 (0.779–0.981) for females and males combined. The non-spatial capture-recapture population growth rates were 0.894 (0.758–1.024) for females, 0.825 (0.700–0.948) for males, and 0.863 (0.771–0.957) for both sexes. The combination of low densities, low reproductive rates, and predominantly negative population growth rates suggest that Banff National Park’s population of grizzly bears requires continued conservation-oriented management actions.     

Population growth lags in introduced species

When introduced to new ecosystems, species'' populations often grow immediately postrelease. Some introduced species, however, maintain a low population size for years or decades before sudden, rapid population growth is observed. Because exponential population growth always starts slowly, it can be difficult to distinguish species experiencing the early phases of slow exponential population growth (inherent lags) from those with actively delayed growth rates (prolonged lags). Introduced ungulates provide an excellent system in which to examine lags, because some introduced ungulate populations have demonstrated rapid population growth immediately postintroduction, while others have not. Using studies from the literature, we investigated which exotic ungulate species and populations (n = 36) showed prolonged population growth lags by comparing the doubling time of real ungulate populations to those predicted from exponential growth models for theoretical populations. Having identified the specific populations that displayed prolonged lags, we examined the impacts of several environmental and biological variables likely to influence the length of lag period. We found that seventeen populations (47%) showed significant prolonged population growth lags. We could not, however, determine the specific factors that contributed to the length of these lag phases, suggesting that these ungulate populations'' growth is idiosyncratic and difficult to predict. Introduced species that exhibit delayed growth should be closely monitored by managers, who must be proactive in controlling their growth to minimize the impact such populations may have on their environment.