François Messier

Genetic structure of the world’s polar bear populations

We studied genetic structure in polar bear (Ursus maritimus) populations by typing a sample of 473 individuals spanning the species distribution at 16 highly variable microsatellite loci. No genetic discontinuities were found that would be consistent with evolutionarily significant periods of isolation between groups. Direct comparison of movement data and genetic data from the Canadian Arctic revealed a highly significant correlation. Genetic data generally supported existing population (management unit) designations, although there were two cases where genetic data failed to differentiate between pairs of populations previously resolved by movement data. A sharp contrast was found between the minimal genetic structure observed among populations surrounding the polar basin and the presence of several marked genetic discontinuities in the Canadian Arctic. The discontinuities in the Canadian Arctic caused the appearance of four genetic clusters of polar bear populations. These clusters vary in total estimated population size from 100 to over 10 000, and the smallest may merit a relatively conservative management strategy in consideration of its apparent isolation. We suggest that the observed pattern of genetic discontinuities has developed in response to differences in the seasonal distribution and pattern of sea ice habitat and the effects of these differences on the distribution and abundance of seals.

Generalization of learned predator recognition: an experimental test and framework for future studies

While some prey species possess an innate recognition of their predators, others require learning to recognize their predators. The specific characteristics of the predators that prey learn and whether prey can generalize this learning to similar predatory threats have been virtually ignored. Here, we investigated whether fathead minnows that learned to chemically recognize a specific predator species as a threat has the ability to generalize their recognition to closely related predators. We found that minnows trained to recognize the odour of a lake trout as a threat (the reference predator) generalized their responses to brook trout (same genus as lake trout) and rainbow trout (same family), but did not generalize to a distantly related predatory pike or non-predatory suckers. We also found that the intensity of antipredator responses to the other species was correlated with the phylogenetic distance to the reference predator; minnows responded with a higher intensity response to brook trout than rainbow trout. This is the first study showing that prey have the ability to exhibit generalization of predator odour recognition. We discuss these results and provide a theoretical framework for future studies of generalization of predator recognition.

THE SIGNIFICANCE OF LIMITING AND REGULATING FACTORS ON THE DEMOGRAPHY OF MOOSE AND WHITE-TAILED DEER

SUMMARY (1) I examined the significance of food competition, wolf predation (Canis lupus), and snow accumulation as limiting or regulating factors of moose (Alces alces) and white-tailed deer (Odocoileus virginianus). That is, I assessed the contribution of those factors in creating year-to-year variations in animal abundance, or in generating density dependence. (2) I used long-term data on the demography of moose on Isle Royale, Michigan, and deer in the National Superior Forest, north-eastern Minnesota. (3) Wolf predation and food competition explained 80% of the interannual variation of moose abundance. Snow accumulation had no quantifiable effect on moose numbers. Competition for food, but not wolf predation and snow, had a regulatory impact on moose. (4) Wolf predation was inversely related to moose density and the relationship differed between periods of moose expansion and reduction. The dual density relationship of wolf predation may explain population cyclicity of moose at elevated densities. (5) Significant inverse relationships were found between deer population growth and relative wolf density, as well as with deer density. Snow had no measurable effect on deer numbers, possibly because of extremely low deer densities and the predominant impact of wolf predation. (6) A previous suggestion that snow accumulation during consecutive winters creates a cumulative impact on the nutritional status of deer and moose was not supported.

Intraspecific Variation in Home Range Overlap with Habitat Quality: A Comparison among Brown Bear Populations

We developed a conceptual model of spatial organization in vertebrates based upon changes in home range overlap with habitat quality. We tested the model using estimates of annual home ranges of adult females and densities for 30 populations of brown bears (Ursus arctos) in North America. We used seasonality as a surrogate of habitat quality, measured as the coefficient of variation among monthly actual evapotranspiration values for areas in which study populations were located. We calculated home range overlap for each population as the product of the average home range size for adult females and the estimated population density of adult females. Home range size varied positively with seasonality; however, home range overlap varied with seasonality in a nonlinear manner. Areas of low and high seasonality supported brown bears with considerable home range overlap, but areas of moderate seasonality supported brown bears with low home range overlap. These results are consistent with behavioural theory predicting a nonlinear relationship between food availability and territoriality.

Population delineation of polar bears using satellite collar data

To produce reliable estimates of the size or vital rates of a given population, it is important that the boundaries of the population under study are clearly defined. This is particularly critical for large, migratory animals where levels of sustainable harvest are based on these estimates, and where small errors may have serious long-term consequences for the population. Once populations are delineated, rates of exchange between adjacent populations can be determined and accounted/corrected for when calculating abundance (e.g., based on mark-recapture data). Using satellite radio-collar locations for polar bears in the western Canadian Arctic, we illustrate one approach to delineating wildlife populations that integrates cluster analysis methods for determining group membership with home range plotting procedures to define spatial utilization. This approach is flexible with respect to the specific procedures used and provides an objective and quantitative basis for defining population boundaries. See ful...

Learning by embryos and the ghost of predation future

Most research on the effects of exposure to stressful stimuli during embryonic development has focused on post-embryonic behaviour that appears to be abnormal or maladaptive. Here, we tested whether exposure to some stressful stimuli (predatory cues) can lead to post-embryonic behaviour that is adaptive. When eggs of ringed salamanders (Ambystoma annulatum) were exposed to chemical cues from predators, post-hatching larvae showed reduced activity and greater shelter-seeking behaviour; larvae that had been exposed to control cues did not show these behaviours. In addition, wood frog (Rana sylvatica)tadpoles learned to respond to chemical cues from unfamiliar predators with danger based on embryonic conditioning. Therefore, if embryonic experience is a good predictor of future risk, learning associated with exposure to negative stimuli during development may be adaptive.

INFLUENCE OF SEA ICE DYNAMICS ON HABITAT SELECTION BY POLAR BEARS

Polar bears live in high-latitude environments characterized by cyclic variation in form and extent of sea ice. From 1991 to 1995, we used radio telemetry and monthly satellite images to compare patterns of ice selection by 110 female polar bears, relative to two geographic regions and four seasons. We hypothesized that extreme seasonal changes in ice characteristics in the Baffin Bay region, including a period of open water, may limit polar bear density despite supporting greater prey density than the Archipelago region, where ice is present year-round. Using cyclic time series analysis to model seasonal variation, we found differences in level, amplitude, and phase between sea ice characteristics and habitat selection by polar bears of the Arctic Archipelago and Baffin Bay regions. Polar bears not only followed seasonal changes, but they anticipated seasonal fluctuations, e.g., polar bears were found close to ice edges in spring in advance of the peak availability of edges. Also, seasonal selection of sea ice by polar bears was generally of a larger amplitude than cycles in ice and is best explained by intensive use of specific ice types in spring and summer, and sparse use during the remaining year. During spring and summer, Archipelago bears used landfast ice more intensively, whereas Baffin bears used moving ice, defined as thick first-year ice found in large floes. Both ice types likely represent areas where most seal pupping occurred in spring for each region. Bears from both regions selected first-year ice in winter when new ice was forming and multiyear ice in autumn when maximum ice melt had occurred. Overall, polar bear selection of ice habitat was similar between regions despite major differences in seasonal ice characteristics. Polar bear density may not directly relate to prey density, due to the limited ability of bears to track the extreme seasonal fluctuations in ice extent found in more productive environments.

SOCIAL ORGANIZATION AND SPACE USE OF COYOTES IN EASTERN CANADA RELATIVE TO PREY DISTRIBUTION AND ABUNDANCE

Abstract We studied the influence of prey size and abundance on social organization and space use by eastern coyotes (Canis latrans) in 2 areas of Nova Scotia, Canada. Breeding pairs formed the nucleus of coyote social groups, and these often traveled with 1–3 other coyotes during winter. Increased use of white-tailed deer (Odocoileus virginianus) was insufficient to explain group size and cohesiveness by eastern coyotes. Winter-traveling group size was similar for family groups using deer (X̄ = 2.6) or snowshoe hares (X̄ = 2.7) as a primary prey in winter. Estimated densities of coyotes in winter was 4.3–13.9 coyotes/100 km2. Coyotes used the same general areas during winter and summer and from year to year. However, territory sizes decreased with increasing densities of deer (partial r2 = 0.21, P = 0.043) and hares (partial r2 = 0.40, P = 0.007). During winter, coyotes used areas of high deer density in proportion to their availability, but in some instances, they used areas that contained few or no deer proportionately more than expected, probably because deep snow and few trails increased vulnerability of deer in these areas. Territoriality seemed to prevent coyotes from concentrating in deer wintering areas and kept the coyote : deer ratio relatively low (<1:25).

Can prey exhibit threat-sensitive generalization of predator recognition? Extending the Predator Recognition Continuum Hypothesis

Despite the importance of predator recognition in mediating predator–prey interactions, we know little about the specific characteristics that prey use to distinguish predators from non-predators. Recent experiments indicate that some prey who do not innately recognize specific predators as threats have the ability to display antipredator responses upon their first encounter with those predators if they are similar to predators that the prey has recently learned to recognize. The purpose of our present experiment is to test whether this generalization of predator recognition is dependent on the level of risk associated with the known predator. We conditioned fathead minnows to chemically recognize brown trout either as a high or low threat and then tested the minnows for their responses to brown trout, rainbow trout (closely related predator) or yellow perch (distantly related predator). When the brown trout represents a high-risk predator, minnows show an antipredator response to the odour of brown trout and rainbow trout but not to yellow perch. However, when the brown trout represents a low-risk predator, minnows display antipredator responses to brown trout, but not to the rainbow trout or yellow perch. We discuss these results in the context of the Predator Recognition Continuum Hypothesis.

The nose knows: minnows determine predator proximity and density through detection of predator odours

Prey often face a behavioural trade-off between fitness-related activities and costly predator avoidance. Individuals that are able to assess their level of risk should maximize their fitness by allocating appropriate amounts of time and energy to avoid predators. The threat-sensitive predator avoidance hypothesis states that prey should respond to a given threat with an intensity that matches their level of risk. Prey fish are known to assess predation risk using predator odours. However, the level of sophistication of risk assessment based on predator odours is not well understood. We conducted two experiments to investigate whether fathead minnows, Pimephales promelas, assess proximity and density of pike, Esox lucius, predators based on pike odours. In experiment 1, we exposed pike-experienced minnows to either 60 ml of pike odour from 12 pike (i.e. 5 ml/pike), 60 ml of pike odour from two pike (i.e. 30 ml/pike) or a control of 60 ml of water. Minnows exposed to odours from two pike showed a more intense antipredator response than did minnows exposed to odours from 12 pike, demonstrating that minnows can detect individual pike in a mixture of odours from several pike. The fact that minnows responded with a greater intensity as the per-pike concentration increased while the overall concentration of pike odour remained constant, indicates that minnows can use odours to determine their relative proximity to predators. In experiment 2, we exposed pike-experienced minnows to either 5 ml/pike from each of 12 pike, 5 ml/pike from each of two pike or a water control. Minnows in the 12-pike treatment showed a stronger antipredator response than did minnows in the two-pike treatment, demonstrating that minnows can assess the relative density of predators using predator odours. These results demonstrate an amazing level of sophistication of predator odour assessment; they are the first to show that prey fish can use odours to determine predator proximity and relative density to respond to predators in a threat-sensitive manner.