Stephen M. Arthur

Trophic relations of brown and black bears in several western North American Ecosystems

We examined the historical and current diets of brown bears (Ursus arctos) and black bears (U. americanus) in the Greater Yellowstone Ecosystem, Glacier National Park and immediately adjacent areas of national forests, Cabinet-Yaak mountains of northwestern Montana and northern Idaho, Blackfeet and Flathead Indian reservations east and south of Glacier National Park, the Kenai Peninsula of Alaska, and the southwestern states of Colorado, New Mexico, and Arizona. Dietary estimates are an essential first step in understanding variation in productivity and density of current populations and, therefore, predicting success of reintroduced populations. Hair or bone samples from 14 federal or state agencies, museums, and universities were examined via stable isotope analyses to quantify the importance of animal and plant resources to sympatric brown and black bears. Stable isotope analyses have numerous advantages over fecal analyses or direct observation because diets of (1) individuals and thereby specific age and sex classes within a population can be compared, and (2) long-dead bears can be compared to living bears to evaluate historical changes in ecosystems. Meat content of current brown bear diets, which varied extensively between individuals and age and sex classes in all populations, averaged 51 ± 19% (x ± SD) for subadult and adult males and females in the Greater Yellowstone Ecosystem and 11 ± 14% in Glacier National Park and Cabinet-Yaak mountains. Within these ecosystems, adult male brown bears were more carnivorous than any other age or sex class. Brown bears that used easily obtained, abundant meat sources had dietary meat contents generally ≥70%. The meat:plant ratios in the diets of historical Greater Yellowstone Ecosystem bears (1,000 YBP) and Glacier National Park bears (1908-18) were similar to ratios in current diets. Sympatric black bears in the Wyoming, Montana, and Idaho ecosystems had dietary meat:plant ratios that were not different from all brown bear age and sex classes, except adult males. Alaskan black bears made extensive use of salmon (Oncorhynchus spp.) when brown bears were rare (53 ± 28% of the diet), but did not use salmon when sympatric with abundant brown bears.

Monitoring coyote population dynamics by genotyping faeces

Reliable population estimates are necessary for effective conservation and management, and faecal genotyping has been used successfully to estimate the population size of several elusive mammalian species. Information such as changes in population size over time and survival rates, however, are often more useful for conservation biology than single population estimates. We evaluated the use of faecal genotyping as a tool for monitoring long‐term population dynamics, using coyotes (Canis latrans) in the Alaska Range as a case study. We obtained 544 genotypes from 56 coyotes over 3 years (2000–2002). Tissue samples from all 15 radio‐collared coyotes in our study area had ≥ 1 matching faecal genotypes. We used flexible maximum‐likelihood models to study coyote population dynamics, and we tested model performance against radio telemetry data. The staple prey of coyotes, snowshoe hares (Lepus americanus), dramatically declined during this study, and the coyote population declined nearly two‐fold with a 11/2‐year time lag. Survival rates declined the year after hares crashed but recovered the following year. We conclude that long‐term monitoring of elusive species using faecal genotyping is feasible and can provide data that are useful for wildlife conservation and management. We highlight some drawbacks of standard open‐population models, such as low precision and the requirement of discrete sampling intervals, and we suggest that the development of open models designed for continuously collected data would enhance the utility of faecal genotyping as a monitoring tool.

Dispersal of juvenile fishers in Maine

We studied natal dispersal of fishers (Martes pennanti) in a harvested population in southcentral Maine during 1984-90 because of concern over the high level of harvest and a lack of information about fisher dispersal. Probability that an individual would disperse by the end of its first year was 73 and 100% for males and females, respectively (n = 21 M, 12 F). However, 32% of males and no females dispersed before the age of 9 months. Mean distance between natal and adult home ranges did not differ (t = 0.16, P = 0.88) between males (n = 8, x = 10.8 km, range = 4.1-19.5) and females (n = 5, x = 11.2 km, range = 5.0-18.9). Dispersal, in combination with intrasexual territoriality of adults, may limit fisher density and competition for food

Predator-Mediated Indirect Effects of Snowshoe Hares on Dall's Sheep in Alaska

Abstract Indirect interactions among species can strongly influence population dynamics and community structure but are often overlooked in management of large mammals. We estimated survival of Dalls sheep (Ovis dalli) in the central Alaska Range, USA, during years of differing snowshoe hare (Lepus americanus) abundance to test whether indirect interactions with a cyclic hare population affect Dalls sheep either negatively, by subsidizing predators (apparent competition), or positively, by diverting predation (apparent commensalism). Annual survival of adult female sheep was consistently high (0.85 for all yr and age classes combined). In contrast, annual estimates of lamb survival ranged from 0.15 to 0.63. The main predators of lambs were coyotes (Canis latrans) and golden eagles (Aquila chrysaetos), which rely on hares as their primary food and prey on lambs secondarily. Coyotes and eagles killed 78% of 65 radiocollared lambs for which cause of death was known. Lamb survival was negatively related to hare abundance during the previous year, and lamb survival rates more than doubled when hare abundance declined, supporting the hypothesis of predator-mediated apparent competition between hares and sheep. However, stage-specific predation and delays in predator responses to changes in hare numbers led to a positive relationship between abundance of adult Dalls sheep and hares. Lacking reliable estimates of survival, a manager might erroneously conclude that hares benefit sheep. Thus, support for different indirect effects can be obtained from different types of data, which demonstrates the need to determine the mechanisms that create indirect interactions. Long-term survey data suggest that predation by coyotes is limiting this sheep population below levels typical when coyotes were rare or absent. Understanding the nature of indirect interactions is necessary to effectively manage complex predator–prey communities.

Use of faecal genotyping to determine individual diet

Abstract Faecal genotyping has been proposed as a method to examine the diets of individuals, but this application has been virtually unexplored by wildlife biologists. We used faecal genotyping and conventional scat analysis to determine the diets of 42 coyotes Canis latrans belonging to nine social groups in Alaska. We use rarefaction to examine the effect of scat sample size on the accuracy and precision of individual diets, and we simulate diets from scats to determine how diet richness and evenness affect sample size requirements. We then demonstrate the utility of this technique by examining variation in diet among individual coyotes and social groups in relation to prey availability. Estimates of diet diversity and composition were highly variable when <10 scats were used to construct the diet. Diets simulated with a uniform (i.e. even) distribution of prey items required generally smaller sample sizes to estimate diet diversity and richness than diets with exponentially distributed items; however, items in actual scats were exponentially distributed. We found moderate dietary variability among individuals in our study area, and diet overlap was higher among coyotes within social groups than between groups. As predicted by optimal foraging theory, the niche widths of all coyote groups expanded as their primary prey (the snowshoe hare Lepus americanus) became scarce during our three-year study. Despite increased niche width, diet overlap among groups remained constant, suggesting that coyotes selected differing alternative prey. Spatiotemporal variation in snowshoe hare availability explained 70% of the variation in hare consumption among groups, indicating that variation in local prey availability may be the primary cause of diet variation among coyotes. Although faecal genotyping can be used to address ecological questions at the individual level, studies should be designed specifically for this purpose so that sufficient numbers of faeces can be obtained.

Modeling Caribou Movements: Seasonal Ranges and Migration Routes of the Central Arctic Herd.

Migration is an important component of the life history of many animals, but persistence of large-scale terrestrial migrations is being challenged by environmental changes that fragment habitats and create obstacles to animal movements. In northern Alaska, the Central Arctic herd (CAH) of barren-ground caribou (Rangifer tarandus granti) is known to migrate over large distances, but the herd’s seasonal distributions and migratory movements are not well documented. From 2003–2007, we used GPS radio-collars to determine seasonal ranges and migration routes of 54 female caribou from the CAH. We calculated Brownian bridges to model fall and spring migrations for each year and used the mean of these over all 4 years to identify areas that were used repeatedly. Annual estimates of sizes of seasonal ranges determined by 90% fixed kernel utilization distributions were similar between summer and winter (X̅ = 27,929 SE = 1,064 and X̅ = 26,585 SE = 4912 km2, respectively). Overlap between consecutive summer and winter ranges varied from 3.3–18.3%. Percent overlap between summer ranges used during consecutive years (X̅ = 62.4% SE = 3.7%) was higher than for winter ranges (X̅ = 42.8% SE = 5.9%). Caribou used multiple migration routes each year, but some areas were used by caribou during all years, suggesting that these areas should be managed to allow for continued utilization by caribou. Restoring migration routes after they have been disturbed or fragmented is challenging. However, prior knowledge of movements and threats may facilitate maintenance of migratory paths and seasonal ranges necessary for long-term persistence of migratory species.

DISEASE COMPLEXITY IN A DECLINING ALASKAN MUSKOX (OVIBOS MOSCHATUS) POPULATION

Abstract The muskox (Ovibos moschatus) population inhabiting the eastern North Slope (ENS) of Alaska, US declined dramatically during 1999–2006, whereas populations in western Alaska (WA) were stable or increasing. To understand morbidity and mortality factors contributing to the decline, Alaska Department of Fish and Game conducted pathologic investigations of carcasses from 2005 until 2008. Additionally, archived sera from both ENS and WA muskoxen collected during 1984–92, before the documented beginning of the ENS decline; sera collected during 2000, near the beginning of the decline; and contemporary sera (from live capture–release, adult females) collected during 2006, 2007, and 2008 were analyzed to determine whether prevalence of antibody to potential pathogens differed in the two areas or changed over time. The pathogens investigated were those that were believed could cause lameness or poor reproduction or adversely affect general health. Furthermore, trace mineral levels, hemograms, and gastrointestinal parasites were evaluated in live adult females captured 2006–08. Pathologic investigations identified several comorbid conditions, including predation, polyarthritis caused by or consistent with Chlamydophila spp. infection, hoof lesions, copper deficiency, contagious ecthyma, verminous pneumonia, hepatic lipidosis suggestive of negative energy balance, and bacterial bronchopneumonia due to Trueperella pyogenes and Bibersteinia trehalosi. Pathogens suspected to be newly introduced in the ENS muskox population on the basis of serologic detection include bovine viral diarrhea, respiratory syncytial virus, Chlamydophila spp., Brucella spp., Coxiella burnetii, and Leptospira spp., whereas parainfluenza virus-3 antibody prevalence has increased in the WA population. Although multiple disease syndromes were identified that contributed to mortality and, in combination, likely limited the ENS muskox population, further holistic investigations of disease agents, trace mineral status, and nutritional factors in conjunction with intensive demographic and environmental analyses would provide a better understanding of factors that influence Alaskan muskox populations.

Effects of grizzly bear predation on muskoxen in northeastern Alaska

Abstract Muskoxen (Ovibos moschatus) are thought to be highly effective at defending themselves from predators. However, a decline in muskox abundance in northeastern Alaska, USA, that coincided with several instances of grizzly bear (Ursus arctos) predation observed during 2000–2006 raised concerns about the effects of predation on this population. In response, from 2007 to 2011 we estimated rates of reproduction and survival and determined rates and causes of muskox mortality on the arctic coastal plain of northeastern Alaska. Annual counts of muskox abundance (x̄ = 191) and estimates of population growth (x̄ = 0.94) indicated a stable or slowly declining population. Annual natality ranged from 0.45 to 0.86 (x̄ = 0.68) births/adult female, whereas annual survival ranged from 0.40 to 0.63 (x̄ = 0.49) for calves and from 0.73 to 0.91 (x̄ = 0.83) for adult females. Predation by grizzly bears was the most common cause of death among cases where a cause could be identified, accounting for 58% and 62% of deaths of calves and adults, respectively. Most bear predation occurred during late winter and spring when little other food was available to bears. The importance of predation compared with other mortality factors, and the change from a growing to a declining muskox population, suggest a change in either predator abundance or behavior. There is no evidence that bear abundance changed dramatically during this period, but abundance of moose (Alces alces) and caribou (Rangifer tarandus) declined substantially in the area where the muskox decline was most pronounced. This suggests bears may have increased predation on muskoxen in response to reduced availability of other ungulates. Maintaining diversity of native ungulates may help bears cope with the natural fluctuations in prey abundance often seen in arctic ecosystems.