Fred L. Bunnell

Modeling the Sustainable Harvest of Female Polar Bears

We explored ttir boundaries of sustainable harvest of polar bears (Ursus maritimus) by considering a range of values for population parameters in a discrete, age specific model structured to mimic polar bear life history. Survival rate of adult females is the predominant factor affecting population growth rate and sustainable harvest of polar bears although other factors may also be significant; e.g.. cub survival, litter size, and age of 1st reproduction. The parameter of least imimrtance is litter production rate. Deferred reproduction has a small effect 011 population growth rate. ’fliese findings are consistent with theoretical predictions for populations experiencing density indeimideiit mortality mainly restricted to juveniles. ‘rhe critical issue. when considering the long-term effect of any harvest, is the effect on numbers of breeding females. Under optimal conditions tlw siistainalde yield of adult female polar bears is typically <1.6% of the total popillation. J. WILDL. MANAGE. 51(4):811-820 W e use a model to explore the constraints that polar bear life history s t ructure places on sustainable rates of harvest. W e develop a mathematical description of polar bear life history, including harvest as a separate source of mortality. By simulating several harvest types, t h e model yields information on t h e effects of harvest types and o n the sensitivity of the harvest to changes in vital rates (parameter values). Additionally, a “best case” scenario can be developed using maximum values for survival a n d reproduction. Funding for this work was provided by the Norsk Polarinstitutt, Dep. Renewable Resour., Gov. Northwest Territ. , the Univ. British Columbia, a n d t h e Mich. State Agric. Exp. Stn. W e thank S. C. Amstrup, M. C. S. Kingsley, T. Larsen, L. J. Lee, j. W . Lentfer, P. E. Mills, N. A. Oritsland, M. A. Ramsay, I. G. Stirling, a n d K. Ugland for their comments a n d for discussions 812 POLAII BEAR H A I I V E S I ~ Taylor et al. J . Wildl. Manage 51(4):1987 that led to this work. M. Bromley, N. J . Lunn, and J . S. Pin edited the text. C;. L. Locke arid J . E. Troje prepared the figures. l’he life history pattern of polar bears is typical of species in which environrnerital fluctuations strongly affect recruitment rate antl survival of the young (tlairston et al. 1970; Schaffer 1974a,b; Stearns 1977; llorn 1978; Goodman 1979, 1981). Polar bears are a long-lived, late maturing species with a low rate of annual recruitment (Dehbster and Stirling 1981). Polar bears exhibit “birth pulse” (Cauglilry 1977) reproduction. Typically, a small fraction of polar bear females breed for the 1st time at age 3, and slightly more begin breeding at age 4. Generally all females breed at adult rates from age 5 onwards (initial age = 0). However. age specific litter production rates vary according to environmental conditions (Stirling et al. 1975, 1977, 1978). During the 1st 2 years following birth, cubs remain with the female and she is unavailable for breeding. Some females with cubs lose their litters and become available for breeding at the next season. Females with 2-year-old cubs are ready for breeding because virtually all cubs are weaned at 2.5 years (Stirling et al. 1975, DeMaster and Stirling 1981). In arly given year, however, 30-60% of the available adult females do not breed or are not impregnated (Lentfer et al. 1980; I . Stirling, pers. commun.) The breeding season for polar bears is from early spring to early summer. Cubs are born in late December or January (L0ne 1970, Lentfer 1976) antl are called cubs-of-the-year or COY’S to distinguish them from older cubs. Data from captive polar bears suggest that, typically, 2 young are born (Kostyan 1954). However, because of intrauterine and den mortality, the average litter size of adult females ranges from 1.58 to 1.87 (L0n

Biodiversity across spatial and temporal scales: problems and opportunities

Both researchers and practitioners confront difficulties when addressing issues that underlie efforts to maintain biological diversity in managed forests. Many difficulties are conceptual but encouraged by practical concerns. They can be loosely categorized into three broad themes: (1) simplification of complexity, (2) loosely defined concepts, and (3) categorization and isolation. Simplified research and management are contrary to maintaining complexity and diversity; loosely specified concepts hinder translation of research into management action; and isolated, neatly categorized studies create management problems when fine-scale studies are transferred to broad-scale management. We review the scales that nature gives us and the scales we construct, then illustrate how differences in given and constructed scales impede research and management. We suggest some steps towards solution that can aid the contribution of reliable knowledge to management and reduce elements of risk associated with management actions.

Sexual Segregation and Female Grizzly Bear Avoidance of Males

We examined seasonal use of habitat for 14 male and 5 female grizzly bears (Ursus arctos) in southwestern Alberta, 1981-84, to test 2 competing hypotheses regarding segregation of the sexes. The male avoidance hypothesis predicts increasing differences in use of habitat with increasing male use of female-occupied areas because of female avoidance of males. The no avoidance hypothesis predicts decreasing differences in use of habitat with increasing male use of female-occupied areas because of increasing similarity of available habitat. Differences in use of habitat were greatest during late summer, when many males concentrated in the female-occupied area, and they were less during other seasons when few males were in the female-occupied area

Characterizing independence of observations in movements of columbian black-tailed deer

Lack of independence in observations of animal locations and movements can cause underestimates of home-range sizes and may lead to inappropriate interpretations of temporal use of space. We used Schoeners Ratio (1981) to assess independence of observations in movements of black-tailed deer (Odocoileus hemionus columbianus). We examined the time interval between samples at which independence would occur with, and without, migratory movements, using 12,510 locations from 44 resident and 28 migratory deer. Most datasets contained dependent, or redundant, observations. Even with a 6-week interval between samples (i.e., 8 samples/yr), observations were still dependent for >50% of the deer tested. We found similar results when the data tested represented distance between consecutive locations rather than the locations themselves

Tests of hypotheses for sexual segregation in grizzly bears

We studied 2 grizzly bear (Ursus arctos) populations to test 3 hypotheses of sexual segregation. The no avoidance hypothesis predicts that females do not avoid males and male-occupied habitats but simply have different habitats available to them within their home ranges. The food hypothesis predicts that subadult and adult females avoid males because of competition or cannibalism by males for food. The sex hypothesis predicts that only sexually mature adult females avoid males because of sexually motivated infanticide by nonsire males. Sexually mature females avoided (P < 0.05) food-rich, male-occupied habitats in Kananaskis, Alberta, but selected (P < 0.05) such habitats in the Selkirk Mountains of Idaho. Sexually immature females selected (P < 0.05) food-rich, male-occupied habitats in both areas. Unequal availability of habitat did not explain the pattern of segregation because food-rich habitats were available to all age-sex classes. Competition or cannibalism by males did not explain segregation because only sexually mature females avoided male-occupied habitats in Kananaskis and no females avoided males in the Selkirks. Adult female avoidance of potentially infanticidal, nonsire, immigrant males in Kananaskis appeared to explain the pattern of segregation. High mortality of older males in Kananaskis coincided with an influx of younger, potentially infanticidal, immigrant males, and adult females avoided those males and their favored habitats. No such segregation was observed in the Selkirks where mortality of older males was low and where there were few or no immigrant males. Results are inconsistent with the no avoidance and food hypotheses but consistent with the sex hypothesis of sexual segregation.

Possible negative effects of adult male mortality on female grizzly bear reproduction

We studied 2 grizzly bear (Ursus arctos) populations to test 3 hypotheses on the effects of adult male mortality on female reproduction. The “no effect” hypothesis predicts that reproduction should be higher in the population with superior overall diet quality, regardless of mortality of adult males. The “increased reproduction” hypothesis predicts that reproduction should be higher in the hunted population because of lowered numbers of competitive or cannibalistic adult males. The “decreased reproduction” hypothesis predicts that reproduction should be lower in the hunted population because of increased immigration by potentially infanticidal, nonsire males with subsequent reduced survival of cubs, and/or increased sexual segregation resulting in reduced production of cubs. Reproduction rates were 0.46 in a hunted population in Kananaskis, Alberta and 0.74 in non-hunted populations in the Selkirk Mountains of Idaho and British Columbia. Mean litter size was smaller in Kananaskis than in the Selkirks (1.40 vs 2.22) but age at first parturition was earlier in Kananaskis (5.50 vs 7.30 years). Mean birth intervals were not different between populations. Age of mothers, overall diet quality, and total population density were not associated with differences in litter size and age at first reproduction, but adult female avoidance (sexual segregation) of nonsire immigrant males and associated food-rich habitats were. Our results are inconsistent with the “no effect” and “increased reproduction” hypotheses but consistent with the “decreased reproduction” hypothesis. Higher hunting mortality of older males coincided with higher numbers of potentially infanticidal, immigrant males in Kananaskis. Adult females avoided those males and their food-rich habitats in Kananaskis and female reproduction appeared to suffer as a result.

Dynamics of a small, hunted brown bear Ursus arctos population in Southwestern Alberta, Canada

Abstract We studied population dynamics of brown bears Ursus arctos in the Kananaskis Park and Bow Crow Forest of southwestern Alberta, Canada to evaluate effects of hunting. Twenty-four bears were captured and 20 were radio-monitored from 1980 to 1984. Estimated density was 1.6 bears/100 km 2 , for a population size of 38 bears. Mean annual sex and age composition was 30% adult males, 22% adult females, 22% subadult males, 11% subadult females, and 15% cubs. Mean litter size of new cubs was 1.40 and mean birth or breeding interval was 3.00 years. The reproductive rate was estimated at 0.46 cubs/adult female/year. Adjusted annual survival rates were 0.70 for adult males, 0.93 for adult females, 0.89 for subadult males, 0.89 to 0.93 for subadult females, and 0.78 for cubs. Combined, these rates yield population growth rates of r s = −0.01 to r s = + 0.01. Increased hunting mortality of older adult males coincided with an influx of younger immigrant males, which apparently contributed to low reproductive rate and population decline.

Relationships between transmission of solar radiation and coniferous forest stand characteristics

Abstract Transmission of global, direct, diffuse, and diffuse photosynthetically active solar radiation through coniferous forest canopies was studied on 12 plots during sunny days in summer. The proportions of radiation transmitted were a function of forest stand characteristics and differed among radiation components. The relationship between the proportion of diffuse radiation transmitted and stand characteristics differed among stand structures, but transmission of direct radiation did not differ. When direct beam radiation was scattered by open crowns of short trees and crowns extended within the height of radiation sensors, diffuse radiation within the canopy was higher than outside the stand. The extent to which different forest stand characteristics predict transmission and approximate a model analogous to Beers law was explored. Sum of tree diameters and Reinekes stand density index were the better predictors of tranmission of global ( i 2 =0.80−0.95) and direct radiation ( i 2 =0.70−0.98). Overstory cover predicted transmission of diffuse radiation best ( i 2 =0.74) when bases of tree crowns were above sensors. The same forest stand characteristics obtained by different sampling methods gave different predictabilities of the components transmitted. Differences were found between hemispherical photograph estimates of transmission of diffuse radiation and measured transmission of diffuse solar and diffuse photosynthetically active radiation. Photographic estimates of transmission of direct radiation differed from measured transmission of direct radiation.

Population dynamics of Selkirk Mountains Grizzly bears

We investigated population dynamics of grizzly bears (Ursus arctos) in the Selkirk Mountains Grizzly Bear Ecosystem (SMGBE) of Idaho, Washington, and British Columbia to assist grizzly bear recovery from threatened status. We captured and radiomonitored 28 bears from 1985 to 1990. Estimated densities were 1.41 ± 0.14 (95 % CL) and 2.33 ± 0.36 bears/100 km 2 for the U.S. and Canadian portions of the SMGBE, respectively. Litter size (cubs ≤ 1.5 yr) was 2.22 ± 0.26 and mean birth interval was 3.0 ± 0.5 years for an estimated reproductive rate of 0.74 ± 0.10 cubs/adult female per year. Age at first parturition was 7.3 ± 0.38 years. Estimated annual survival rates were 0.96 ± 0.05 for adult females, 0.81 ± 0.20 for adult males, 0.78 ± 0.22 for subadult females, 0.90 ± 0.17 for subadult males, and 0.84 ± 0.16 for cubs

Persistence of Black-Tailed Deer Fecal Pellets in Coastal Habitats

The persistence of fecal pellets from Columbian black-tailed deer (Odocoileus hemionus columbianus) was determined for 2 levels of 3 environmental factors: moisture, substrate, and canopy. Pellet persistence was least in moist, vegetated forest and greatest in dry, bare cutover. After 1 year, the mean number of pellets remaining in pellet groups on moist sites was between 16 and 48% of the original complement of 50 pellets. On dry sites between 50 and 70% of the pellets were present after 1 year. Similar trends occurred for visibility of pellet groups. After 2 years, 5-25% of the pellet groups were visible at moist, cutover sites, whereas 25-75% of the pellet groups were visible at dry, cutover sites. Rates of change of pellet group visibility indicate that the number of pellet groups counted on uncleared plots represent from 1 to 3 x the number of pellet groups that were deposited the previous year. J. WILDL. MANAGE. 51(1):33-37 Pellet group surveys are an established method for studying ungulate density in North America. There are, however, disagreements about the utility of pellet group counts (Collins and Urness 1981, Leopold et al. 1984). The assumptions made to interpret pellet group data are reviewed by Robinette et al. (1958) and Neff (1968) who evaluated pellet count techniques and offered improvements to statistical design. Assumptions made to interpret pellet counts (Neff 1968) are violated for some conditions, thereby invalidating results. Persistence and visibility of pellet groups are factors affecting counts (Wallmo et al. 1962, Fisch 1979) but are rarely attributed much importance. That pellet groups persist for the duration of the deposition period is commonly assumed. Persistence after the deposition period has been addressed by clearing plots or marking existing pellet groups. Methods developed to minimize the influence of differing persistence or visibility, such as clearing plots, are time consuming and sometimes impractical. Although problems are associated with pellet group counts, their simplicity makes them a desirable technique and ensures their continued use by wildlife managers. Our objectives were to measure pellet persistence and visibility in different habitats. Three factors are important in determining pellet group persistence: moisture, substrate, and canopy cover. Evaluation of the direction and magnitude of effects impos d by these factors on pellet group persistence and visibility should allow more reliable interpretation of past results, extension of present findings, and improved sampling design. The B.C. Fish and Wildl. Branch, Can. For. Products Co. Ltd., Univ. British Columbia, and This content downloaded from 157.55.39.177 on Sat, 19 Nov 2016 04:38:53 UTC All use subject to http://about.jstor.org/terms 34 PELLET PERSISTENCE * Harestad and Bunnell J. Wildl. Manage. 51(1):1987 Natl. Sci. and Eng. Res. Counc. provided support through grants to F. L. Bunnell. Simon Fraser Univ. provided computer support.