Article

Climate and reproduction of grizzly bears in Yellowstone National Park

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Abstract

CONTROVERSY surrounds the conflicts between the requirements of human safety and the preservation of grizzly bears (Ursus arctos horribilis) in western North America. It has been difficult to separate the effect of factors such as the closure of garbage dumps from that of the climate. It has also proved difficult to relate climatic data to changes in the populations of large mammals. I report here a correlation of climatic change with fluctuations in the sizes of litters of grizzly bears born in Yellowstone National Park, Wyoming, during 1958-1976. The decrease in litter sizes observed since the closure of garbage dumps seems to be largely a consequence of unfavourable weather during the periods of the final fattening of the mother, winter sleep, birth, lactation and early spring foraging. This study represents one of the few times that the effects of climate have been demonstrated for large omnivorous or carnivorous mammals.

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... The natural environment or carrying capacity for grizzly bears in and around Yellowstone National Park appears to fluctuate widely from year to year (Knight and others 1984). Natural control factors that directly affect the population or indirectly affect it by promoting human-caused mortality have only been nominally explored (Picton 1978;Picton and Knight in press). Effective management is unlikely unless the interaction between the human and natural regimes is understood and appropriately weighted. ...
... Thus, the population is at carrying capacity and is undergoing K selection. This is further confirmed by the litter size-climate relationships previously reported (Picton 1978 ;Picton and Knight in press). This paper examines some of the mechanisms by which a population responds to climatic variation . ...
Conference Paper
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For a quarter century the Yellowstone grizzly bear population inspired public controversy. The major hypothesis has been that human-caused mortality is a primary influence upon this population. The effects of natural controlling factors have only been nominally explored. Habitat available to the population is characterized by sporadic and widely fluctuating food production primarily controlled by weather. The natural carrying capacity of the overall habitat fluctuates accordingly. During years of low carrying capacity, bears compensate by using a larger area and more of them are likely to die. The naturally low reproductive rate of the grizzly bear precludes quick population adjustment to fluctuating carrying capacity. Management strategies should therefore be geared to a worst-case situation. Indexes of food availability for each habitat type are computed and related to climatic conditions. The range of climatic conditions that can be expected is estimated from recent weather records. The worst-case climatic and food-producing situation is then described and can be prepared for.
... En cada corrida se consideró una reducción de K de un 20% en años de catástrofes. La frecuencia de años catastróficos se estimó cada 20 años y con un año de duración de cada evento, basado en las estadísticas climáticas obtenidas mediante un índice medioambiental (Picton, 1978) y de registros esporádicos de años extremos. ...
... Entre estas últimas cabe destacar una tormenta de nieve ocurrida en el área de estudio en el invierno de 1995 (con 5m de nieve en algunos sectores) y otros eventos climáticos como sequías y años con precipitaciones intensas que habrían extinguido localmente varios grupos de huemules. En relación a las implicaciones de las variaciones medioambientales y catástrofes climáticas, Picton (1978) consideró que las variaciones en los factores climáticos como la precipitación podrían usarse como un índice para la variación de disponibilidad de alimento y de este modo evaluar la incidencia de los eventos medioambientales que afectan a la población. Este tipo de índice también se ha usado para varias especies de grandes ungulados, a fin de relacionar supervivencia de crías con abundancia de alimento. ...
Article
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In order to evaluate the population projection for the huemul of the south (Hippocamelus bisulcus) in Central Chile (Nevados de Chillán), a stochastic simulation model was applied. This population has continually decreased in size over the last decade and empirical estimates suggest that in a short time the current relicts of this population would extinguish locally. The simulation model was applied using life history and environmental data. Survival rate, mean fecundity and carrying capacity were modeled over a time span of 100 years. The population age structure, sex ratio and local density average were deter mined on the basis of historical (1975-2003) records. The results indicate that this is a high risk population with a mean extinction time between 27 and 42 years. The population decline could be explained by effects generated mainly by sustained anthropic perturbation occurring in a large proportion of primary habitats and by stochastic environmental perturbations. The relevance of several protection measures is discussed, including increment for the area of available primary habitat, conservation of corridors among fragments, and translocation of individuals from the existing southern populations in XI Region of Chile.
... En cada corrida se consideró una reducción de K de un 20% en años de catástrofes. La frecuencia de años catastróficos se estimó cada 20 años y con un año de duración de cada evento, basado en las estadísticas climáticas obtenidas mediante un índice medioambiental (Picton, 1978) y de registros esporádicos de años extremos. ...
... Entre estas últimas cabe destacar una tormenta de nieve ocurrida en el área de estudio en el invierno de 1995 (con 5m de nieve en algunos sectores) y otros eventos climáticos como sequías y años con precipitaciones intensas que habrían extinguido localmente varios grupos de huemules. En relación a las implicaciones de las variaciones medioambientales y catástrofes climáticas, Picton (1978) consideró que las variaciones en los factores climáticos como la precipitación podrían usarse como un índice para la variación de disponibilidad de alimento y de este modo evaluar la incidencia de los eventos medioambientales que afectan a la población. Este tipo de índice también se ha usado para varias especies de grandes ungulados, a fin de relacionar supervivencia de crías con abundancia de alimento. ...
Article
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Se aplicó un modelo de simulación estocástico para evaluar la proyección numérica de la población del huemul del sur (Hippocamelus bisulcus) en Chile Central (Nevados de Chillán), población en la que se ha observado una disminución persistente durante las últimas décadas. Estimaciones empíricas sugieren que en poco tiempo sus relictos actuales se extinguirían localmente. Se aplicó un modelo de simulación que incluye datos de historia de vida y de variaciones ambientales. La tasa de supervivencia, el tamaño medio de camada y capacidad de carga fueron modelados a lo largo de 100 años. Se determinó la estructura de edades y sexo de la población actual y la tendencia de la densidad promedio por sitio en base a registros históricos (1975-2002). El modelo aplicado indicó que esta población de huemules se encuentra en alto riesgo, con un tiempo medio de extinción entre 27 y 42 años. La disminución de la población de huemules podría ser explicada por efectos generados principalmente por factores antrópicos, que se mantienen en la mayoría de los sitios de hábitat primario, y por perturbaciones ambientales estocásticas. Se discute la importancia de medidas de protección, como ampliación del área de hábitat primario disponible, conservación de corredores entre fragmentos y traslocación de huemules desde la población sur (XI Región).
... Causal links between climate and closure vs. litter size are not known and can only be inferred until confirmed by field research. However, the only obvious ways that this worsening of the climate might have affected litter size are by reducing natural food supply or increasing thermoregulatory costs of living (Picton 1978). ...
... However, for now, we have no conclusive evidence that bear litter size changes with maternal age independently of nutritional status and body size. Picton (1978), by contrast, demonstrated a direct correlation between litter size and climatic favorability; he thus attributed the litter size decline to climatic worsening rather than to dump closure. Reanalysis of this correlation, however, shows that climate can account for only about 20% of the litter size decline, whereas events associated with dump closure account for the other 80%. ...
Article
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Grizzly bears (Ursus arctos) in Yellowstone National Park fed heavily on garbage at open-pit dumps from about 1895 until the dumps were closed in 1968-71. Concurrent with dump closure, mean cub litter size declined 17%. Almost 20% of the decline was associated with coincidental worsening of the climate and nearly 80% with closure. Impacts of closure may have been compounded by the simultaneous increase in adult male abundance, to which litter size was negatively correlated.
... Numerous management actions fatal to bea rs also attended closure of the dwnps Craighead 1971, Knight andEberhardt 1985). These factors, as well as probable worsened climatic conditions (Picton 1978, Picton et al. 1985 have resulted in a precarious status for Yel lowstone ' s grizzly popula t ion. Knight and Eberhardt (1984) hypothesize loss of one or two additional females per year could lead to eventual extinction. ...
Technical Report
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Increasing levels of backcountry human use may constitute unacceptable added stress to Yellowstone's grizzly population . In response to this concern, the Interagency Grizzly Bear Committee (IGBC) directed the Interagency Grizzly Bear Study Team (IGBST) to conduct research designed to approximate the effects of backcountry recreation activity on individual grizzly bears. The ultimate goal of this study effort was to determine if demonstrable negative impacts result from human intrusion. Results from the first year of study (Schleyer et al. 1984) indicated bears were generally displaced if approached closer than 370 m by field teams during the diurnal period. Results of the 1985 field season are contained in this report .
... Bears (Ursidae) are prominent members of the mammalian fauna wherever they are found and include the largest of the Carnivora as well as some of the largest of terrestrial mammals (Nowak & Paradiso, 1983). They are, or were recently found, on all continents except Australia and Antarctica. ...
Article
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Data on age-specific natality rates, litter size, interbirth interval, age of first reproduction, reproductive senescence, age of weaning and cub survival were determined for a free-ranging population of polar bears inhabiting Hudson Bay, Canada, near the southern limit of the species range. Serum progesterone levels were also determined for females at different stages of their reproductive cycle to provide corroborative support for the reproductive parameters described. Animals were live captured using immobilizing drugs and each animal uniquely marked for future identification. First parturition occurred at four or five years of age and the age-specific natality rate increased with age until approximately 20 years, after which it dropped markedly. At least 40% of adult females displayed two-year interbirth intervals and 55% of cubs in their second year were independent of their mother. Mean size of cub litters in spring was 1.9 and 13% of litters had three or more cubs. The natality rate for 5–20-year-old females was estimated as 0.9, higher than that reported for any more northerly polar bear populations where two-year interbirth intervals are rare, fewer than 5% of yearling cubs are weaned and triplet litters occur with less than 1% frequency. Cub mortality was initially high and declined with age. Although cubs in western Hudson Bay were weaned at a younger age and a lighter weight than their counterparts in more northern populations, cub mortality rates were similar. The reason for the marked differences in reproductive parameters in the western Hudson Bay population is not known. We speculate that sea-ice conditions may be sufficiently different to allow weaned bears at a lighter body weight to hunt seals more successfully there than further north.
... Numerous threatened species are attracted to sources of food created by human activity [e.g. garbage (Picton, 1978;Yirga et al., 2012), carrion (Roy & Dorrance, 1985;Guinard, Julliard & Barbraud, 2012) and agricultural products (Sukumar, 1990;Naughton-Treves et al., 1998)]. All of these anthropogenic foods may occur along roads and railways (e.g. ...
Article
Transportation corridors can attract threatened wildlife via habitat enhancement and foraging opportunities, leading to collisions with vehicles. But wildlife may also be attracted to energy-dense food products that are spilled or discarded from moving vehicles, which is rarely studied. Therefore, we quantified train-spilled attractants in Banff and Yoho National Parks, Canada, where agricultural products (hereafter, grain) are transported along 134 km of railway and may contribute to wildlife mortality. We measured grain deposition from 2012 to 2015 at 19 sites and assessed the performance of three structures developed to measure spilled grain. We then modeled grain deposition with respect to four types of spatial and temporal variables: those related to grain shipment, physical habitat characteristic, train-related characteristics and variables specific to the study site. Grain was spilled at a mean rate of 1.64 g m�2 day�1 (SD = 3.60) from April to October (n = 3 years) and 1.52 (SD = 2.37) from November to March (n = 1 year). Extrapolating annual deposition across the study area yielded enough grain (110 tons) to provide 4.77 9 108 kcal of gross energy, which is equivalent to the average annual caloric needs of 42–54 grizzly bears Ursus arctos horribilis; the regional population is estimated at 50–73 animals. Much of this energy will not be accessible or available to bears; however, their attraction to it could contribute to rising and unsustainable rates of mortality. Models explained 9–31% of the variance in deposition for each grain type, primarily via coarse temporal variables of shipping rates and month. The absence of more specific predictive variables suggests that mitigation should target broader policies, such as prompt reporting and repair of leaky hopper cars, and limits to train stoppage in protected areas. We encourage more global assessment of the under-studied issue of food attractants spilled by vehicles along transportation corridors.
... Mean litter size has been correlated with adult female body mass, intake of dietary meat, primarily salmon and ungulates (Bunnell and Tait 1981;Stringham 1990;McLellan 1994;Hilderbrand et al. 1999a); and garbage (Stringham 1986). Litter size also has been related to latitude (Bunnell and Tait 1981;Stringham 1984), climate, and a climate-carrion index (Picton 1978;Picton and Knight 1986); there are exceptions (Wielgus and Bunnell 2000). Litter size also is age related, with young and old females producing fewer cubs per litter than prime-age adults (J.J. Craighead et al. 1974Craighead et al. , 1995aSellers and Aumiller 1994). ...
... reproductive success (Picton 1978, Costello et al. 2003. As a measure of potential changes in resource availability, we derived annual potential evapotranspiration (PET hereafter) from daily temperate data using Thornthwaite (1948Thornthwaite ( ) equation (1970Thornthwaite ( -2012. ...
... For instance, directional changes in habitat quality associated with natural processes, human impact and management regulations can drive long-term fluctuations in abundance and spatial distribution [8,[14][15][16][17]. In addition, there is evidence that survival and reproductive parameters are modulated by changes in resource availability associated with changing climatic conditions [18,19]. On the other hand, complex behavioural syndromes like sexually selected infanticide (SSI) [20,21] or reproductive suppression between females [22], might result in intrinsic, density-dependent regulation. ...
Article
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Understanding what factors drive fluctuations in the abundance of endangered species is a difficult ecological problem but a major requirement to attain effective management and conservation success. The ecological traits of large mammals make this task even more complicated, calling for integrative approaches. We develop a framework combining individual-based modelling and statistical inference to assess alternative hypotheses on brown bear dynamics in the Cantabrian range (Iberian Peninsula). Models including the effect of environmental factors on mortality rates were able to reproduce three decades of variation in the number of females with cubs of the year (Fcoy), including the decline that put the population close to extinction in the mid-nineties, and the following increase in brown bear numbers. This external effect prevailed over density-dependent mechanisms (sexually selected infanticide and female reproductive suppression), with a major impact of climate driven changes in resource availability and a secondary role of changes in human pressure. Predicted changes in population structure revealed a nonlinear relationship between total abundance and the number of Fcoy, highlighting the risk of simple projections based on indirect abundance indices. This study demonstrates the advantages of integrative, mechanistic approaches and provides a widely applicable framework to improve our understanding of wildlife dynamics. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
... Mean litter size has been correlated with adult female body mass, intake of dietary meat, primarily salmon and ungulates (Bunnell and Tait 1981;Stringham 1990;McLellan 1994;Hilderbrand et al. 1999a); and garbage (Stringham 1986). Litter size also has been related to latitude (Bunnell and Tait 1981;Stringham 1984), climate, and a climate-carrion index (Picton 1978;Picton and Knight 1986); there are exceptions (Wielgus and Bunnell 2000). Litter size also is age related, with young and old females producing fewer cubs per litter than prime-age adults (J.J. Craighead et al. 1974Craighead et al. , 1995aSellers and Aumiller 1994). ...
... Black bears and grizzlies raid squirrel middens to feed on lipid-rich whitebark pine seeds, especially in the fall, preceding hibernation (Mealey 1975;Picton 1978;Kendall 1980a, b). We agree with Kendall (1980a) that bears do not obtain whitebark pine cones by breaking branches from tree crowns, but rely on squirrel hoards. ...
Article
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Whitebark pine (Pinus albicaulis) is known to have its seeds harvested and cached in the soil by Clark's Nutcracker (Nucifraga columbiana), and unretrieved seeds are known to be capable of germinating and establishing new pines. Many other vertebrates also harvest and feed on these seeds, however, and the roles of these animals as dispersers and establishers of whitebark pine has been uncertain. This work demonstrates that birds other than the nutcracker, rodents, and other mammals do not have the requisite behaviors to systematically disperse or establish whitebark pine, and that the pine is therefore dependent on the nutcracker for its regeneration. These findings support previous suggestions that Clark's Nutcracker is a specialized frugivore that has profoundly influenced the ecology and the evolution of whitebark pine.
... There are few other regions where the influence of climate on basic ecosystem attributes has been as well documented as the Greater Yellowstone Ecosystem (GYE). Research has shown that elk, bison, and grizzly bear populations in the GYE are tightly linked to annual climate variation (Meagher 1976, Picton 1978. Authors have shown that the distribution of vegetation types in Grand Teton and Yellowstone National Parks is influenced by the seasonality of precipitation (Despain 1987(Despain , 1990. ...
Article
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There are few other regions where the influence of climate on basic ecosystem attributes has been as well documented as the Greater Yellowstone Ecosystem (GYE). Research has shown that elk, bison, and grizzly bear populations in the GYE are tightly linked to annual climate variation (Meagher 1976, Picton 1978). Authors have shown that the distribution of vegetation types in Grand Teton and Yellowstone National Parks is influenced by the seasonality of precipitation (Despain 1987, 1990). Natural disturbances, especially fires and insect outbreaks, are also known to coincide with specific climate scenarios in this region (Knight 1987, Balling et al. 1992). Therefore, understanding how climate can vary over time is essential for the proper management of these areas (Luckman 1996). Modem instrumental records have contributed greatly to our understanding of the current GYE climate system. In particular, work by Mock (1996) and Bartlein et al. (1997) has demonstrated how local manifestations of large-scale circulation patterns produce distinct climates within the GYE. In addition, studies using modem climate records and General Circulation Models by Balling et al. (1992) and Bartlein et al. (1997) have identified trends toward increasing aridity in the GYE and the potential for these trends to continue well into the future. Late Pleistocene and Holocene (18-1 kya) climate in the GYE is known mainly from lake­sediment cores. Work by Whitlock (1993), Whitlock and Bartlein (1993), and Thompson et al. (1993) indicates that after deglaciation, increased solar radiation during summer months led to a highly seasonal climate regime. As levels of solar radiation changed through the Holocene, GYE climate became increasingly more like today until the modem regime became established around 1500-1600 AD (Whitlock 1993, Elias 1997). While existing modem and paleoecological studies reveal important aspects of the GYE climate system, there is a distinct lack of high-resolution data for most of the last millennium. Lake sediments only record climate variation at a resolution of hundreds to thousands of years, and instrumental records do not exist before the 1890s. Dendroclimatology, the study of climate using patterns of tree-ring growth (Fritts 1976) is particularly well suited to fill this gap in our knowledge of GYE climate. Tree-rings have been used successfully for climate reconstructions worldwide, offer records spanning decades to millennia, and can provide annual resolution. Therefore, we are developing a network of tree-ring sites in the western Absaroka Mountains and eastern Bighorn Basin to fill important spatial (areas east of Yellowstone NP) and temporal (high resolution for the past 700-1,000+year) gaps in our knowledge of GYE climate.
... Extensive consumption of dry fruits in autumn could be indispensable for hibernating females that give birth and stay in the den with the cubs until April. Because detailed data on food availability only exist for selected areas, we used forest cover of masting species ( bosque ) and annual precipitation ( prec ) as potential surrogates of mast production (Picton 1978;Wiegand et al. 1998 ). As an indicator of spatial heterogeneity, and hence habitat productivity for spring and summer herbs and berries, we used an index of landscape ruggedness ( rug ), calculated as x ϩ SD, where x is the mean value of the slope and SD the standard deviation calculated on the 25 1-km 2 squares forming each 25-km 2 cell. ...
Article
We developed a conceptual framework for classifying habitat quality that requires the construction of separate habitat models for each key demographic feature; the framework can be applied when the factors that determine different demographic processes differ substantially. For example, survival of large carnivores is mainly determined by human-induced mortality, whereas nutritional condition determines reproductive rate. Hence, a two-dimensional habitat model built for reproduction and survival yields five hypothetical habitat categories: matrix, with no reproduction and/or very high mortality; sink, with low reproduction and high mortality; refuge, with low reproduction and low mortality; attractive sink, with high reproduction and high mortality; and source, with high reproduction and low mortality. We applied this framework to two endangered brown bear ( Ursus arctos ) populations in the Cantabrian Mountains, Spain. Our aim was to generate working hypotheses about the quality and spatial arrangement of bear habitat to analyze the present conditions of the different population nuclei and to facilitate identification of core areas of high conservation value, conflictive areas, or areas with unoccupied potential habitat. We used a geographic information system and two spatial long-term data sets on presence and reproduction and performed logistic regressions for building a two-dimensional model. The analysis reveals that both populations exist under different suboptimal conditions: the eastern population mainly occupies areas of suboptimal natural habitat and relatively low human impact, whereas the western population is located mainly in areas with high human impact but otherwise good natural quality. To test hypotheses about demographic features of the obtained habitat categories, we classified data on historic extinction in northern Spain ( fourteenth to nineteenth centuries ) with the two-dimensional model. Extinction probabilities within each habitat category confirmed the hypotheses: most extinctions occurred in matrix habitat, and the fewest occurred in source habitat. Resumen: Desarrollamos un marco conceptual para clasificar la calidad del hábitat que requiere la construcción de modelos de hábitat separados para cada característica demográfica clave. El marco se puede aplicar cuando difieren sustancialmente los factores que determinan diferentes procesos demográficos. Por ejemplo, la supervivencia de grandes carnívoros esta determinada principalmente por mortalidad inducida por humanos, mientras que la condición nutricional determina la tasa reproductiva. Consecuentemente, un modelo bidimensional del hábitat construido para reproducción y supervivencia produce cinco categorías hipotéticas de hábitat: matriz ( sin reproducción y/o mortalidad muy alta ), sumidero ( reproducción baja, mortalidad alta ), refugio ( reproducción baja, mortalidad baja ), sumidero atractivo ( reproducción alta, mortalidad alta ) y fuente ( reproducción alta, mortalidad baja ). Aplicamos este marco a dos poblaciones en peligro de oso pardo ( Ursus arctos ) en la Cordillera Cantábrice, España. Nuestra meta fue generar hipótesis de trabajo sobre la calidad y la distribución espacial del hábitat de los osos para analizar las condiciones actuales de los diferentes núcleos de población, para facilitar la identificación de áreas núcleo de alto valor de conservación, áreas conflictivas o áreas con hábitat potencial desocupado. Utilizamos un sistema de información geográfica y dos conjuntos de datos históricos de presencia y reproducción y aplicamos regresiones logísticas para construir un modelo bidimensional. El análisis revela que ambas poblaciones existen bajo diferentes condiciones sub-óptimas: la población oriental ocupa principalmente áreas de hábitat natural sub-óptimo y relativamente bajo impacto humano, mientras que la población occidental se localiza principalmente en áreas con alto impacto humano, pero por lo demás con buena calidad natural. Para evaluar las hipótesis sobre las características demográficas de cada tipo de hábitat, clasificamos datos de extinciones históricas en el norte de España ( siglos XIV a XIX ) con el modelo bidimensional. Las probabilidades de extinción en cada categoría de hábitat confirmaron las hipótesis: la mayoría de las extinciones ocurrieron en hábitat matriz y la minoría ocurrió en hábitat fuente.
... However , our data show reasonable differences between observed cub mortality and mean litter sizes (Table 2A) in bad and good years, as defined by our simple climatic index. A similar climatic index (Picton 1978) has been used by to predict grizzly bear litter size in Yellowstone. considered that variations in climatic data, especially precipitation , could be used as an index for the variation of food availability. ...
Article
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The status of the brown bear (Ursus arctos) in Spain has suffered a dramatic decline during the last centuries, both in area and numbers. Current relict populations are suspected to be under immediate risk of extinction. The aim of our model is to attain an understanding of the main processes and mechanisms determining population dynamics in the Cordillera Cantabrica. We compile the knowledge available about brown bears in the Cordillera Cantabrica, northern Spain, and perform a population viability analysis (PVA) to diagnose the current state of the population and to support current management. The specially constructed simulation model, based on long-term field investigations on the western brown bear population in the Cordillera Cantabrica, includes detailed life history data and information on environmental variations in food abundance. The method of individual-based modeling is employed to simulate the fate of individual bears. Reproduction, family breakup, and mortalities are modeled in annual time steps under the influence of environmental variations in food abundance, mortality rates, and reproductive parameters. In parallel, we develop an analytical model that describes the mean behavior of the population and that enables us to perform a detailed sensitivity analysis. We determine current population parameters by iterating the model with plausible values and compare simulation results with the 1982-1995 time pattern of observed number of females with cubs of the year. Our results indicate that the population suffered a mean annual decrease of ~4-5% during the study period, 1982-1995. This decrease could be explained by a coincidence of high poaching pressure with a series of climatically unfavorable years during the period 1982-1988. Thereafter, population size probably stabilized. We estimate that the population currently consists of 25 or 26 independent females and a total of 50-60 individuals. However, our viability analysis shows that the population does not satisfy the criterion of a minimum viable population if mortalities remain at the level of the last few years of 1988-1995. The 'salvation' of at least one independent female every three years is required. The population retains relatively high reproductive parameters, indicating good nutritive conditions of the habitat, but mortality rates are higher than those known in other brown bear populations. The most sensitive parameters, adult and subadult mortality of females, form the principal management target. Our model shows that the series of females with cubs contains valuable information on the state of the population. We recommend monitoring of females with cubs as the most important management action, both for collecting data and for safeguarding the most sensitive part of the population.
Article
Data on the population of grizzly bears in the environs of Yellowstone National Park suggest that the population has not recovered from the reductions following closure of garbage dumps in 1970 and 1971, and may continue to decline. A computer simulation model indicates that the risk of extirpation over the next 30 yr is small, if the present population parameters continue to prevail. A review an further analysis of the available data brings out the importance of enhancing adult female survival if the population is to recover, and assesses various research needs. In particular, a reliable index of population trend is needed to augment available data on the population. 12 references, 9 figures, 6 tables.
Article
Initial appraisals of the status of endangered large-mammal populations may have to depend on indices of population trend. Such indices may possibly be improved by using auxiliary variables. Various models were studied for populations of the Florida manatee (Trichechus manatus latirostris), Yellowstone grizzly bear (Ursus arctos horribilis), and Hawaiian monk seal (Monachus schauinslandi). Several criteria for checking validity of the fitted models were considered, and the simple R2 criterion appears to provide useful comparisons. Multiple regression models overestimated the rate of change of the East Coast manatee population as determined from three other sources (a covariance model, a non-linear model, and the rate estimated from reproductive and survival data). A multiple regression model for grizzly bears using three auxiliary variables exhibited a fairly high R2 (0.84) and appeared to provide a better fit than did a non-linear model. A beach count index for Hawaiian monk seals seemed to be unreliable for year-to-year comparisons in contrast to total population counts and estimates from a capture-recapture method. The use of auxiliary variables for checking and improving trend index data appears feasible and well worthwhile.
Article
Various interpretations of the Craighead team data on Yellowstone grizzly bears (Ursus arctos horribilis) are reviewed. The Craigheads continue to favor a noncompensatory model that gives the greatest likelihood of population extinction with an increased mortality rate. McCullough (1981) found that recruitment of cubs and survivorship of juveniles were influenced by adult population size. Stringham (1983) reached most of the same conclusions by different methods. McCullough (1981), Stringham (1983), and Shatffer (1978, 1983) all reported negative relationships between adult population size (or adult males only) and percent of females producing litters and mean litter size. Time lags in the density-dependent effect of adults on cub recruitment were treated by Avrin (1976) with slightly different results. All authors have emphasized the susceptibility of grizzly bear populations to overexploitation, although the impact varies with model assumptions. Shaffer (1978, 1983) examined stochastic variables as they influence minimum viable population size. A congruence analysis was done for the McCullough (1981) model in which parameters were run in model simulations to test model responses to observed results for the years of the Craighead study. This analysis reaffirmed the oscillatory behavior of the population and showed that oscillatory behavior decreased as the adult mortality rate increased. Great fluctuations in population parameters make assessment of the current status of the population difficult. An alternate strategy of long-term population monitoring and management based on a systematized aerial count of minimum unduplicated bears is proposed. Int. Conf. Bear Res. and Manage. 6:21-32 The conflict over the status and management of the grizzly bear population in Yellowstone National Park began in 1967 with a disagreement between the John and Frank Craighead research team and the National Park Service biologists and administrators over the procedures for closing open-pit garbage dumps (Craighead and Craighead 1967, 1971; Cole 1971). The Craigheads recommended phasing out the dumps over a 10-year-period and simultaneously kill- ing elk (Cervus elaphus) in the backcountry to attract bears away from developed areas. The Park Service chose to close dumps as rapidly as possible and did not shoot elk. Controversy quickly followed (Craig- head et al. 1973, 1974; Cole 1971, 1973; Meagher 1978), and the issue was broadly reported in the press (Craighead 1973, Johnson 1973, Seater 1973, Gilbert 1976, Cauble 1977, Schullery 1980).
Article
An exceptionally rich paleontological site containing thousands of mammalian fossils and well-dated with 18 radiocarbon samples provides evidence of late-Holocene ecological response to climatic change in northern Yellowstone National Park, Wyoming. The mammalian fauna, composed of 10,597 identified specimens, shows surprising affinity to the local habitat with little evidence of long-distance transport of faunal elements, thus revealing the faithfulness of a fossil site to the community from which it is derived. The mammals illustrate ecological sensitivity to a series of mesic to xeric climatic excursions in the sagebrush-grassland ecotone during the past 3200 yr. From 3200 cal yr B.P. to a maximum of 1100 cal yr B.P., the species composition of mammals indicates wetter conditions than today. Beginning about 1200 cal yr B.P., the fauna becomes more representative of xeric conditions with maxima in xeric-indicator taxa and minima in mesic-indicator taxa, concordant with the Medieval Warm Period (circa 1000 to 650 yr B.P.). Cooler, wetter conditions which prevailed for most of the Little Ice Age (700 to 100 yr B.P.) in general correspond to a return to a more mesic mammalian fauna. A warm period within the Little Ice Age is documented by a xeric fauna. These data show that mammalian ecological sensitivity to climatic change over this intermediate time scale holds promise for predictions about the impacts of future global warming.
Article
During June 1993 and 1994, 11 radiocollared and 7 unmarked grizzly bears (Ursus arctos) were monitored visually (observation) from fixed-wing aircraft to document predation on calves of the Porcupine Caribou (Rangifer tarandus) Herd (PCH) in northeastern Alaska, Twenty-six (72%) grizzly bear observations were completed (greater than or equal to 60 min) successfully (median duration = 180 min; +/-95% CI = 136-181 min; range = 67-189 min) and 10 were discontinued (duration less than or equal to 24 min) due to disturbance to the bear, or unfavorable weather conditions. Of the 26 successfully completed observations, 15 (58%) included predatory activity (encounter) directed at caribou calves and 8 (31%) included kills. Of 32 encounters, 9 resulted in kills, for a success rate of 28%. The median duration of encounters was 1 minute (+/-95% CI = 1-2 min: range = 1-6 min: n = 32; ), and the median time spent at a kill was 14 minute (+/-95% CI = 9-23 min: range = 6-56 min; n = 9). Sows with young (n = 4) killed more frequently (75%; P = 0.0178) than barren sows, boars, and consorting pairs combined (17%; n = 18). Estimated kill rate was highest for sows with young (6.3 kills/bear/day; n = 4), followed by barren sows (4.6 kills/bear/day; n = 5), boars (1.9 kills/bear/day; n = 5), and, finally, consorting pairs (1.0 kills/bear/day; n = 8). Estimated kill rate obtained via conventional radiotracking point surveys (4.8 kills/bear/day) was higher than that obtained via concurrent bear observations (3.1 kills/bear/day). Our research provides baseline estimates of predation rates by grizzly bears on caribou calves that will enhance the capability of wildlife professionals in managing populations of both predators and their prey.
Article
A sign of deviation type of index was used to convert standard temperature and precipitation data into a readily used form for the study of deer population dynamics. Statistically significant correlations between the climate index and mule deer fawn survival were demonstrated for four different mule deer populations in Montana. These correlations led to reasonable biological hypotheses delineating the linkage between climate and fawn survival in each of the four areas. The correlations support the frequent observations in the wildlife literature concerning the importance of summer and winter range. They also suggest that human activities may interact with climate in a manner which affects deer fawn survival. In general, in these areas, fawn survival was favored by relatively warm-moist summer, warm-dry winter and cool-dry hunting season weather. The apparent affect of spring weather was variable. Fawn survival in two areas was enhanced by cool-dry summer weather. This reversed response could be the result of human use of the areas, including livestock grazing. It is concluded that this index of climatic fluctuations can be a versatile and useful tool in assessing the impact of climate upon deer populations. In general, weather can be described as a strong biasing factor even when direct effects cannot be consistently demonstrated.
Article
The elk (Cervus canadensis) population was mainly self-regulated by density-influenced mortality from intraspecific competition for food and compensating natality and survival. Mortality higher than usual was mainly due to weather that also increased the vulnerability of elk to predation by grizzly bears (Ursus arctos). Grizzly predation with competitive scavenging was a nonessential but assisting adjunct to other natural processes that regulated the elk population. As an interacting unit, bears of different social rank and an associated scavenger fauna probably helped to dampen elk population fluctuations by culling animals with low-energy reserves. The presence of a grizzly population in Yellowstone Park appears essential to have representative natural equilibriums among interacting secondary consumers, to maintain natural relationships between secondary and primary consumers, and to retain the scientific values of ecological systems with an intact native biota.
School of Forestry, Bulletin
  • J. J. Craighead
  • J. R. Varney
  • F. C. Craighead
Symposium on Changes of Climate, Arid Zone Res.
  • H. H. Lamb
Defenders of Wildlife News
  • A. S. Johnson
Proc. Int. Bear Res.
  • S. P. Mealey
Symposium on Changes of Climate
  • H H Lamb
  • HH Lamb
The Northern Yellowstone Elk
  • D B Houston
  • DB Houston