Environmental stress and developmental stability in dentition of the Yellowstone grizzly bears

Asymmetry in bilateral traits is often used to assess an individual'squality and stress resistance, but stress-induced variationin developmental stability is largely undocumented for free-livingpopulations. Over many years, grizzly bears (Ursus arctos horribilis)extensively foraged around garbage dumps in Yellowstone NationalPark. Abrupt closure of these dumps 26 years ago was a severelystressful event and was followed by excessive mortality anda many-fold increase in grizzly home-range size. I examine howthis stress affected developmental stability by comparing dentitionof bears born before and after the dump closure. I predictedthat (1) asymmetry in dentition should be greater in bears bornafter dump closure compared to before closure, and asymmetryin sexually selected canines should change more than nonsexuallyselected premolars following dump closure and (2) the relationshipbetween tooth asymmetry and tooth size should change in thepopulations following the stressful events as compared withpopulations before stressful events. I found that developmentalstability of canines, which are under directional sexual selectionin males, was more responsive to stress compared to that ofmale premolars or female dentition (both under stabilizing selection),and, because of the increased cost of canine production, feweranimals were able to achieve both large size and symmetricaldevelopment of these teeth, and thus the slope of the relationshipbetween fluctuating asymmetry and canine size increased. I concludethat stress appears to act as an honesty-reinforcement mechanismin sexual selection for symmetrical dentition.     

Prevalence of Trichinella spp. in black bears, grizzly bears, and wolves in the Dehcho Region, Northwest Territories, Canada, including the first report of T. nativa in a grizzly bear from Canada

Samples of muscle from 120 black bears (Ursus americanus), 11 grizzly bears (Ursus arctos), and 27 wolves (Canis lupus) collected in the Dehcho Region of the Northwest Territories from 2001 to 2010 were examined for the presence of Trichinella spp. larvae using a pepsin-HCl digestion assay. Trichinella spp. larvae were found in eight of 11 (73%) grizzly bears, 14 of 27 (52%) wolves, and seven of 120 (5.8%) black bears. The average age of positive grizzly bears, black bears, and wolves was 13.5, 9.9, and approximately 4 yr, respectively. Larvae from 11 wolves, six black bears, and seven grizzly bears were genotyped. Six wolves were infected with T. nativa and five with Trichinella T6, four black bears were infected with T. nativa and two with Trichinella T6, and all seven grizzly bears were infected with Trichinella T6 and one of them had a coinfection with T. nativa. This is the first report of T. nativa in a grizzly bear from Canada. Bears have been linked to trichinellosis outbreaks in humans in Canada, and black bears are a subsistence food source for residents of the Dehcho region. In order to assess food safety risk it is important to monitor the prevalence of Trichinella spp. in both species of bear and their cohabiting mammalian food sources.     

Fast carnivores and slow herbivores: differential foraging strategies among grizzly bears in the Canadian Arctic

Categorizing animal populations by diet can mask important intrapopulation variation, which is crucial to understanding a species’ trophic niche width. To test hypotheses related to intrapopulation variation in foraging or the presence of diet specialization, we conducted stable isotope analysis (δ¹³C, δ¹⁵N) on hair and claw samples from 51 grizzly bears (Ursus arctos) collected from 2003 to 2006 in the Mackenzie Delta region of the Canadian Arctic. We examined within-population differences in the foraging patterns of males and females and the relationship between trophic position (derived from δ¹⁵N measurements) and individual movement. The range of δ¹⁵N values in hair and claw (2.0–11.0‰) suggested a wide niche width and cluster analyses indicated the presence of three foraging groups within the population, ranging from near-complete herbivory to near-complete carnivory. We found no linear relationship between home range size and trophic position when the data were continuous or when grouped by foraging behavior. However, the movement rate of females increased linearly with trophic position. We used multisource dual-isotope mixing models to determine the relative contributions of seven prey sources within each foraging group for both males and females. The mean bear dietary endpoint across all foraging groups for each sex fell toward the center of the mixing polygon, which suggested relatively well-mixed diets. The primary dietary difference across foraging groups was the proportional contribution of herbaceous foods, which decreased for both males and females from 42–76 to 0–27% and 62–81 to 0–44%, respectively. Grizzlies of the Mackenzie Delta live in extremely harsh conditions and identifying within-population diet specialization has improved our understanding of varying habitat requirements within the population.     

Serologic survey for infectious canine hepatitis virus in grizzly bears (Ursus arctos) from Alaska, 1973 to 1987

Serum antibody prevalence of infectious canine hepatitis virus was 12% (90 of 725) for grizzly bears (Ursus arctos) from Alaska (USA) during the period 1973 to 1987. Prevalence was highest on Kodiak Island at 29% (37 of 127). Prevalence of exposure at individual collection areas did not change significantly over time. There were no significant sex-specific differences in prevalence. Prevalence was directly related to age, but it was 0% for bears less than 2-yr-old. Young bears which are exposed to the virus may develop clinical disease and die as a result of the infection. This disease may be a factor affecting grizzly bear population dynamics.     

Herbivore influence on soil microbial biomass and nitrogen mineralization in a northern grassland ecosystem: Yellowstone National Park

Microorganisms are largely responsible for soil nutrient cycling and energy flow in terrestrial ecosystems. Although soil microorganisms are affected by topography and grazing, little is known about how these two variables may interact to influence microbial processes. Even less is known about how these variables influence microorganisms in systems that contain large populations of free-roaming ungulates. In this study, we compared microbial biomass size and activity, as measured by in situ net N mineralization, inside and outside 35- to 40-year exclosures across a topographic gradient in northern Yellowstone National Park. The objective was to determine the relative effect of topography and large grazers on microbial biomass and nitrogen mineralization. Microbial C and N varied by almost an order of magnitude across sites. Topographic depressions that contained high plant biomass and fine-textured soils supported the greatest microbial biomass. We found that plant biomass accurately predicted microbial biomass across our sites suggesting that carbon inputs from plants constrained microbial biomass. Chronic grazing neither depleted soil C nor reduced microbial biomass. We hypothesize that microbial populations in grazed grasslands are sustained mainly by inputs of labile C from dung deposition and increased root turnover or root exudation beneath grazed plants. Mineral N fluxes were affected more by grazing than topography. Net N mineralization rates were highest in grazed grassland and increased from dry, unproductive to mesic, highly productive communities. Overall, our results indicate that topography mainly influences microbial biomass size, while mineral N fluxes (microbial activity) are affected more by grazing in this grassland ecosystem. Received: 4 June 1997 / Accepted: 16 December 1997     

Dietary protein content alters energy expenditure and composition of the mass gain in grizzly bears (Ursus arctos horribilis)

Many fruits contain high levels of available energy but very low levels of protein and other nutrients. The discrepancy between available energy and protein creates a physiological paradox for many animals consuming high-fruit diets, as they will be protein deficient if they eat to meet their minimum energy requirement. We fed young grizzly bears both high-energy pelleted and fruit diets containing from 1.6% to 15.4% protein to examine the role of diet-induced thermogenesis and fat synthesis in dealing with high-energy-low-protein diets. Digestible energy intake at mass maintenance increased 2.1 times, and composition of the gain changed from primarily lean mass to entirely fat when the protein content of the diet decreased from 15.4% to 1.6%. Daily fat gain was up to three times higher in bears fed low-protein diets ad lib., compared with bears consuming the higher-protein diet and gaining mass at the same rate. Thus, bears eating fruit can either consume other foods to increase dietary protein content and reduce energy expenditure, intake, and potentially foraging time or overeat high-fruit diets and use diet-induced thermogenesis and fat synthesis to deal with their skewed energy-to-protein ratio. These are not discrete options but a continuum that creates numerous solutions for balancing energy expenditure, intake, foraging time, fat accumulation, and ultimately fitness, depending on food availability, foraging efficiency, bear size, and body condition.     

Leaf litter decomposition in a southern Sonoran Desert ecosystem, northwestern Mexico: Effects of habitat and litter quality

Leaf litter decomposition of dominant woody perennial species in the three most common habitats of the southern Sonoran Desert was studied using the litter-bag method. Our objective was to assess the influence of litter quality on decomposition rates in three contrasting desert environments. The hypotheses were: (1) decomposition rates within the same litter type are faster in more mesic habitats, (2) decomposition rates are lower in higher lignin content or lower nutrient quality substrates, and (3) species-rich substrates enhance decomposition rates. For all litter types and habitats, a rapid loss of mass occurred during the summer rains at the start of the experiment, but total loss within the same litter type differed significantly among habitats. Decay rates were not higher in the more mesic habitat, but in the dry plains where solar irradiance and termite activity were highest. While termite activity was less important in the arroyos and absent in the hillsides habitats, proliferation of fungal mycelium in these sites was much higher than in the plains, suggesting that biotic and abiotic factors act both independently of litter richness. Lignin content seems to be an important factor controlling the loss of litter, because decay rates were inversely related to litter initial lignin content in all three habitats. Leaf litter diversity did not enhance rates of decomposition. The leaf litter mixture had k-values similar to the most recalcitrant monospecific litter in all three habitats, indicating a neutral or even antagonistic role of species-specific compounds in decomposition rates.     

Nearctic earthworm fauna in the southern USA: biodiversity and effects on ecosystem processes

An important aspect of biodiversity is the relative importance of species in the functioning of ecosystems; this is particularly so for the soil biota which regulate organic matter and nutrient dynamics in soil. This paper explores some of the relationships between biodiversity and ecosystem processes, using the example of the nearctic earthworm fauna in the glacial refugium of the southern USA. Competitive exclusion of nearctic earthworm species by exotic species has been postulated but there is little direct evidence of it; habitat alteration is the likely cause of native species decline. Reduced earthworm diversity may or may not strongly affect certain ecosystem processes, but more diverse assemblages may more effectively exploit soil resources and influence a wider array of processes. Nearctic species may be better adapted than exotics to local conditions and thus more strongly influence ecosystem processes. Earthworm communities provide a clear case for the union of functional and taxonomic biodiversity studies, because of the recognized ecological strategies of many species. However, some nearctic taxa may deviate from these strategies. Earthworms utilize course woody debris in forests both as a refuge and a resource, while enhancing the decomposition of wood. Management strategies to maintain or increase biodiversity of soil biota should include residual wood on the forest floor. An important task for ecosystem management is to restore biodiversity in degraded ecosystems; introduction programmes and techniques such as periodic burning may increase the abundance and diversity of native earthworm species. Whole ecosystem conservation and management are probably the most practical ways to conserve biodiversity generally and may be the only ways to maintain soil biodiversity.     

Role of brown bears (Ursus arctos) in the flow of marine nitrogen into a terrestrial ecosystem

We quantified the amount, spatial distribution, and importance of salmon (Oncorhynchus spp.)-derived nitrogen (N) by brown bears (Ursus arctos) on the Kenai Peninsula, Alaska. We tested and confirmed the hypothesis that the stable isotope signature (δ¹⁵N) of N in foliage of white spruce (Picea glauca) was inversely proportional to the distance from salmon-spawning streams (r=–0.99 and P<0.05 in two separate watersheds). Locations of radio-collared brown bears, relative to their distance from a stream, were highly correlated with δ¹⁵N depletion of foliage across the same gradient (r=–0.98 and –0.96 and P<0.05 in the same two separate watersheds). Mean rates of redistribution of salmon-derived N by adult female brown bears were 37.2±2.9 kg/year per bear (range 23.1–56.3), of which 96% (35.7±2.7 kg/year per bear) was excreted in urine, 3% (1.1±0.1 kg/year per bear) was excreted in feces, and <1% (0.3± 0.1 kg/year per bear) was retained in the body. On an area basis, salmon-N redistribution rates were as high as 5.1±0.7 mg/m² per year per bear within 500 m of the stream but dropped off greatly with increasing distance. We estimated that 15.5–17.8% of the total N in spruce foliage within 500 m of the stream was derived from salmon. Of that, bears had distributed 83–84%. Thus, brown bears can be an important vector of salmon-derived N into riparian ecosystems, but their effects are highly variable spatially and a function of bear density. Received: 11 February 1999 / Accepted: 7 July 1999     

Spatial and Temporal Relations between Fluvial and Allacustrine Yellowstone Cutthroat Trout, Oncorhynchus clarki bouvieri, Spawning in the Yellowstone River, Outlet Stream of Yellowstone Lake

Yellowstone cutthroat trout (YCT), Oncorhynchus clarki bouvieri, that spawn in the outlet of Yellowstone Lake show two potamodromous migration patterns, fluvial and allacustrine. The main purpose of this study was to determine whether those fluvial and allacustrine YCT represent reproductively isolated stocks. Redd surveys indicated spawning occurred during about 5 consecutive weeks between late May and mid-July 1993–1995. Lake fish (N=6), defined as radiotagged YCT that entered Yellowstone Lake after the spawning period (i.e. allacustrine pattern), were found in the river between the lake outlet (river kilometer [Rkm] 0) and Rkm 20.0 during spawning. Probable lake fish (N=28; tagged YCT that were last detected near the lake outlet) were found between Rkm 0 and Rkm 22.5 during spawning. River fish (N=4; tagged YCT that remained in the river when annual tracking concluded in fall, i.e. fluvial pattern) were found between Rkm 1.1 and Rkm 18.0 during spawning. Fidelity to spawning areas used between consecutive years was suggested by one of five lake fish and the single river fish for which data were available. Spatial overlap in spawning and a lack of temporal separation between the life-history types during spawning suggested that fluvial and allacustrine YCT were not reproductively isolated. Radiotagging, as well as visual observations made annually from boats during April and May, indicated fluvial YCT overwintered downstream from Rkm 14 and were few, probably on the order of 10% of all YCT that spawned in the Yellowstone River.     

Recent observations of intraspecific predation and cannibalism among polar bears in the southern Beaufort Sea

Intraspecific killing has been reported among polar bears (Ursus maritimus), brown bears (U. arctos), and black bears (U. americanus). Although cannibalism is one motivation for such killings, the ecological factors mediating such events are poorly understood. Between 24 January and 10 April 2004, we confirmed three instances of intraspecific predation and cannibalism in the Beaufort Sea. One of these, the first of this type ever reported for polar bears, was a parturient female killed at her maternal den. The predating bear was hunting in a known maternal denning area and apparently discovered the den by scent. A second predation event involved an adult female and cub recently emerged from their den, and the third involved a yearling male. During 24 years of research on polar bears in the southern Beaufort Sea region of northern Alaska and 34 years in northwestern Canada, we have not seen other incidents of polar bears stalking, killing, and eating other polar bears. We hypothesize that nutritional stresses related to the longer ice-free seasons that have occurred in the Beaufort Sea in recent years may have led to the cannibalism incidents we observed in 2004.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

First report of Taenia arctos (Cestoda: Taeniidae) from grizzly (Ursus arctos horribilis) and black bears (Ursus americanus) in North America

The cestode Taenia arctos was found at necropsy in the small intestine of a grizzly (Ursus arctos horribilis) and a black bear (Ursus americanus) from Kananaskis Country in southwestern Alberta, Canada. The autolysis of the tapeworm specimens precluded detailed morphological characterization of the parasites but molecular analysis based on mitochondrial DNA cytochrome c oxidase subunit 1 gene confirmed their identity as T. arctos. This is the first report of T. arctos from definitive hosts in North America. Its detection in Canadian grizzly and black bears further supports the Holarctic distribution of this tapeworm species and its specificity for ursids as final hosts. Previously, T. arctos was unambiguously described at its adult stage in brown bears (Ursus arctos arctos) from Finland, and as larval stages in Eurasian elk (Alces alces) from Finland and moose (Alces americanus) from Alaska, USA. Given the morphological similarity between T. arctos and other Taenia species, the present study underlines the potential for misidentification of tapeworm taxa in previous parasitological reports from bears and moose across North America. The biogeographical history of both definitive and intermediate hosts in the Holarctic suggests an ancient interaction between U. arctos, Alces spp., and T. arctos, and a relatively recent host-switching event in U. americanus.     

Hunting,Exotic Carnivores,and Habitat Loss: Anthropogenic Effects on a Native Carnivore Community,Madagascar

The wide-ranging, cumulative, negative effects of anthropogenic disturbance, including habitat degradation, exotic species, and hunting, on native wildlife has been well documented across a range of habitats worldwide with carnivores potentially being the most vulnerable due to their more extinction prone characteristics. Investigating the effects of anthropogenic pressures on sympatric carnivores is needed to improve our ability to develop targeted, effective management plans for carnivore conservation worldwide. Utilizing photographic, line-transect, and habitat sampling, as well as landscape analyses and village-based bushmeat hunting surveys, we provide the first investigation of how multiple forms of habitat degradation (fragmentation, exotic carnivores, human encroachment, and hunting) affect carnivore occupancy across Madagascar’s largest protected area: the Masoala-Makira landscape. We found that as degradation increased, native carnivore occupancy and encounter rates decreased while exotic carnivore occupancy and encounter rates increased. Feral cats (Felis species) and domestic dogs (Canis familiaris) had higher occupancy than half of the native carnivore species across Madagascar’s largest protected landscape. Bird and small mammal encounter rates were negatively associated with exotic carnivore occupancy, but positively associated with the occupancy of four native carnivore species. Spotted fanaloka (Fossa fossana) occupancy was constrained by the presence of exotic feral cats and exotic small Indian civet (Viverricula indica). Hunting was intense across the four study sites where hunting was studied, with the highest rates for the small Indian civet (x¯ = 90 individuals consumed/year), the ring-tailed vontsira (Galidia elegans) (x¯ = 58 consumed/year), and the fosa (Cryptoprocta ferox) (x¯ = 31 consumed/year). Our modeling results suggest hunters target intact forest where carnivore occupancy, abundance, and species richness, are highest. These various anthropogenic pressures and their effects on carnivore populations, especially increases in exotic carnivores and hunting, have wide-ranging, global implications and demand effective management plans to target the influx of exotic carnivores and unsustainable hunting that is affecting carnivore populations across Madagascar and worldwide.     

Indicators quantifying small pelagic fish interactions: application using a trophic model of the southern Benguela ecosystem

Three indicators quantifying interactions between species are developed for an upwelling system to provide useful measures for the comparison of marine ecosystem structure and function. Small pelagic fish are dominant in upwelling systems, and by definition, they are pivotal in a wasp-waist upwelling system. The indicator of interaction strength (IS) quantifies the effect that a change in biomass of one group has on abundance of other groups. The functional impact (FI) indicator quantifies the trophic impacts of species on their own and other functional groups or feeding guilds. The trophic replacement (TR) indicator quantifies the trophic similarity between a species that is removed from an ecosystem and other species in that ecosystem, i.e. it quantifies the ability of one group to trophically replace another. A trophic model of the southern Benguela ecosystem is used as an example for the application of the indicators. The strong similarities in trophic functioning of the southern Benguela ecosystem in the anchovy-dominated system of the 1980s, and the 1990s when there was a shift towards greater sardine abundance, are explained by the mutual trophic replacement abilities of anchovy and sardine. Differences between the proposed indicators and mixed trophic impact assessment are highlighted, mainly resulting from the static versus dynamic nature of the models upon which they are based. Trophic indicators such as those presented here, together with other kinds of ecosystem indicators, may assist in defining operational frameworks for ecosystem-based fisheries management.     

Tides,tidal currents and their effects on the intertidal ecosystem of the southern bay,Inhaca Island,Mozambique

Sediment characteristics and tidal currents were studied in the 1500 ha intertidal area south of Inhaca Island,Mozambique. The tide is semi-diurnal with a range at spring of about 3 m. The area connects directly to the oceanthrough the Ponta Torres Strait and (indirectly) through several narrow tidal channels ending up in Maputo Bay.Velocities of up to 0.75 m s^-1 were measured in the Ponta Torres strait. After Low Water, Indian ocean water startsentering the tidal flats, while entrance from the Maputo Bay side is delayed by one to several hours. With onlyone tide gauge and one current meter at hand, we found indications of a higher mean sea level on the oceanic side(probably due to ocean wave set up) and a mean flow in the Ponta Torres Strait directed towards Maputo Bay. Astorm from the SW had a particularly strong influence on the sea level of Maputo Bay, and for a period of a fewdays the current flowed constantly towards Maputo Bay. Measurements in the innermost Saco channel indicatedhigher velocities during ebb than during flood. The resulting residual current will increase sedimentation in the bay,a process which is confirmed by aerial photographs and could be linked to the sanding of the coral reefs and themangrove extension in the area. Extensive sandbanks are situated around both inlets as a result of the higher currentvelocities in these areas, thereby inhibiting the settlement of finer sediments and organic matter. Where the twoflows meet, formation of mudflats and seagrass beds are favoured. Mudflats are found mainly below High WaterNeap, exposed only during spring tides. This longer inundation period favours the settlement of finer material andorganic matter. The area and location of the substrates have great influence on the richness and abundance of thebenthic fauna, as grainsize and organic matter have been correlated with richness and abundance in other studies.