Shane P. Mahoney

Habitat selection at multiple scales 1

Abstract: Habitat selection is the disproportionate use of available conditions and resources, and involves responses in space and time to perceived risks and rewards. It frequently depends on the scale of measurement, often in non-linear ways that preclude simple extrapolation across scales. More critically, animals often select different habitat components at different scales, and species vary in their scales of selection. Although multi-scaled research on habitat selection has proliferated, synthesis of this work has been impeded by imprecise terminology and arbitrarily defined analytical scales. Here, we review key concepts and findings and evaluate future prospects opened up in part by new technologies that enable novel and more efficient data collection. Innovative measurement, combined with novel analytical approaches, permits habitat selection to be investigated across a broad continuum of scales. By linking habitat selection to fitness as a function of scale, use-of-habitat assessments can be more effective. The fitness costs and benefits of habitat selection change with scale; the scales of habitat selection may inform us of limiting factors. We outline how reward/risk ratios can be used to assess the fitness implications of habitat selection across scales.

Hydroelectric development and the disruption of migration in caribou

Abstract We investigated the effects of hydroelectric development on the movements and space-use of caribou ( Rangifer tarandus caribou ) in west-central Newfoundland, Canada. We compared patterns of range use, site fidelity, and timing of migration before, during, and after project construction. Coincidental with the first year of project construction, caribou were less likely to be found within 3 km of the site; this persisted at least 2 years after construction was completed. Relative timing of migration was individual-specific; the rank order of spring arrival on, and autumn departure from, the calving and summer grounds tended to be consistent year-to-year. This is the first report of such individual-specific consistency in migration for a non-avian species. This predictability disappeared during development: the year-to-year consistency of fall and spring migration among individuals was apparent before and after construction, but not during construction. Variation in calving site fidelity was correlated to year-to-year differences in snowfall. We conclude that the development caused a disruption of migrational timing during construction and longer-term diminished use of the range surrounding the project site. Long-term studies of individually marked animals can aid in environmental assessments for migratory animals.

LONG-TERM CHANGES IN DEMOGRAPHY AND MIGRATION OF NEWFOUNDLAND CARIBOU

Abstract Long-term studies of demography and movements are rare but critical to understanding long-lived mobile mammals like caribou (Rangifer tarandus). We studied changes in the abundance, vital rates, body size, and timing of migration of the Buchans Plateau caribou herd in Newfoundland, Canada. From the early 1960s to 2000, the population grew at 6.5%/year, although survival and recruitment indicated a declining growth rate (1.4%) by the late 1990s. The numerical increase was negatively associated with other population attributes. Rates of parturition, survival to 6 months of age, and recruitment diminished significantly. Adults exhibited substantial decreases in body size. Spring migration was significantly later and autumn migration significantly earlier. We surmise that these responses may reflect heightened density-dependent competition for summer forage.

Body Size Variations in Caribou Ecotypes and Relationships With Demography

Abstract In many vertebrates size is one of the most influential and variable individual characteristics and a strong determinant of reproductive success. Body size is generally density dependent and decreases when intraspecific competition increases. Frequent and long-distance movements increase energy expenditures and, therefore, may also influence body size, particularly in highly mobile species. Caribou (Rangifer tarandus, also known as reindeer) exhibit tremendous variation in size and movements and thus represent an excellent candidate species to test the relationships between body size, population size, and movements. We analyzed body measurements of adult female caribou from 7 herds of the Québec-Labrador Peninsula, Canada, and we related their morphology to population size, movements, and annual ranges. The herds represented 3 ecotypes (migratory, montane, and sedentary). Ecotypes and herds differed in size (length), shape (roundness), and movements. The sedentary ecotype was larger and moved 4 to 7 times less than the migratory ecotype in the 1990s. At the start of a demographic growth period in the early 1960s, migratory caribou from the Rivière-George (hereafter George) herd had longer mandibles than caribou of the sedentary ecotype. Mandible length in the George herd declined in the 1980s after rapid population growth, while individuals performed extensive movements and the herds annual range increased. Migratory caribou then became shorter than sedentary caribou. After the George herd decline in the 1990s, mandible length increased again near levels of the 1980s. Caribou from the migratory Rivière-aux-Feuilles herd later showed a similar decline in mandible length during a period of population growth, associated with longer movements and increasing annual range. We hypothesize that the density-dependent effect observed on body size might have been exerted through summer habitat degradation and movement variations during herd growth. Our study has 2 important implications for caribou management: the distinctiveness of different populations and ecotypes, and the correlations between population trajectories and changes in body condition and habitat.

Effects of Progressive Clearcut Logging on Newfoundland Caribou

Abstract Logging has often been implicated in the decline of caribou (Rangifer tarandus), but its effects are incompletely understood. We used a distance-based approach to assess the effects of progressive clearcut logging on the summer (28 May to 15 Sep) range of caribou in Newfoundland, Canada. We compared distances of random locations and of caribou, from 9 years of radiotelemetry, to landcover types across 3 spatial scales: population range, individual ranges, and radiolocations. We tested for incremental avoidance of cutovers and mature softwood forests, the preferred type for caribou and forest harvesting, while controlling for the confounding effects of each. At the individual range, females selected for hardwood and softwood forests, bogs, and barrens, and they avoided open water. Patterns for males were similar, although they avoided bogs and barrens at both scales. The sexes differed in their response to forest harvesting. Females progressively avoided cutovers, both pre- and postharvest, likely due to their spatial proximity. Females maintained an average of 9.2 km from active cutovers. Cutover avoidance was evident even if we controlled statistically for distances to other habitats, and it accounted for heightened disuse of softwood forests. Compared with females, males occurred in proximity, with no incremental response to clearcutting. These results imply deleterious effects of timber harvesting on female caribou. Long-term investigations will enhance our capacity to evaluate such anthropogenic habitat changes.

SPECTRUM OF SELECTION: NEW APPROACHES TO DETECTING THE SCALE-DEPENDENT RESPONSE TO HABITAT

Detecting habitat selection depends on the spatial scale of analysis, but multi-scale studies have been limited by the use of a few, spatially variable, hierarchical levels. We developed spatially explicit approaches to quantify selection along a continuum of scales using spatial (coarse-graining) and geostatistical (variogram) pattern analyses at multiple levels of habitat use (seasonal range, travel routes, feeding areas, and microsites). We illustrate these continuum-based approaches by applying them to winter habitat selection by woodland caribou (Rangifer tarandus caribou) using two key habitat components, Cladina lichens and snow depth. We quantified selection as the reduction in variance in used relative to available sites, thus avoiding reliance on correlations between organism and habitat, for which interpretation can be impeded by cross-scale correlations. By consistently selecting favorable habitat features, caribou experienced reduced variance in these features. The degree to which selection was accounted for by the travel route, feeding area, or microsite levels varied across the scale continuum. Caribou selected for Cladina within a 13-km scale domain and selected shallower snow at all scales. Caribou responded most strongly at the dominant scales of patchiness, implicating habitat heterogeneity as an underlying cause of multi-scale habitat selection. These novel approaches enable a spatial understanding of resource selection behavior.

Effects of Mine Development on Woodland Caribou Rangifer Tarandus Distribution

Abstract Knowledge of the effect of mining developments on caribou Rangifer tarandus is fragmentary. We examined the impact of the Hope Brook gold mine, southwestern Newfoundland, on the La Poile woodland caribou herd on a section of their year-round range. We examined the impact of the mine on caribou distribution during three phases of mine activity (pre-disturbance, construction and open-pit mining and underground mine and mill operation) in five seasons (winter, late winter, pre-calving, calving and autumn). Aerial surveys were conducted on a monthly basis from September 1985 to July 1991. Following initiation of the mine construction, caribou abundance increased with distance from the mine site in all seasons, and caribou avoided areas within 4 km of the site in most seasons. Within 6 km of the mine centre, group size and the number of caribou decreased as mine activity progressed in late winter, pre-calving and calving seasons. Although the impact of the mine was most prominent in the pre-calving and calving seasons, caribou responded to mine disturbance in all seasons. This highlights the importance of evaluating the year-round impact of human-induced environmental change.

Enhanced understanding of predator-prey relationships using molecular methods to identify predator species, individual and sex

Predator species identification is an important step in understanding predator‐prey interactions, but predator identifications using kill site observations are often unreliable. We used molecular tools to analyse predator saliva, scat and hair from caribou calf kills in Newfoundland, Canada to identify the predator species, individual and sex. We sampled DNA from 32 carcasses using cotton swabs to collect predator saliva. We used fragment length analysis and sequencing of mitochondrial DNA to distinguish between coyote, black bear, Canada lynx and red fox and used nuclear DNA microsatellite analysis to identify individuals. We compared predator species detected using molecular tools to those assigned via field observations at each kill. We identified a predator species at 94% of carcasses using molecular methods, while observational methods assigned a predator species to 62.5% of kills. Molecular methods attributed 66.7% of kills to coyote and 33.3% to black bear, while observations assigned 40%, 45%, 10% and 5% to coyote, bear, lynx and fox, respectively. Individual identification was successful at 70% of kills where a predator species was identified. Only one individual was identified at each kill, but some individuals were found at multiple kills. Predator sex was predominantly male. We demonstrate the first large‐scale evaluation of predator species, individual and sex identification using molecular techniques to extract DNA from swabs of wild prey carcasses. Our results indicate that kill site swabs (i) can be highly successful in identifying the predator species and individual responsible; and (ii) serve to inform and complement traditional methods.

Spatial and temporal scaling of population density and animal movement: A power law approach

Abstract Many ecological patterns are sensitive to spatial and temporal scale, but no general protocol has emerged for dealing with scale-dependence. We suggest that power laws, regularly used in the study of body size, can be applied to many such features. We used these techniques to describe two scale-sensitive aspects of caribou (Rangifer tarandus): population densities of North American herds when measured at varying spatial extents, and speeds of radiotracked individuals when observed at varying temporal resolutions. Log-log regression was applied, based on the power formula, Y= cX z. Non-isometric relationships existed for abundance versus area of the population range, but the pattern differed between groups. For sedentary caribou, animal numbers increased more slowly than spatial extent (z = 0.503). For migratory populations, this relationship was hyper-allometric (z > 1), and densities were generally lower for continental herds compared to insular Newfoundland herds living without wolves (Canis lupus). We surmise that defining population bounds may be more subjective for sedentary herds; migratory herd densities may increase with increasing population size. Distance moved versus the interval between radiolocations was also non-isometric (z = 0.551). We standardized these movements to eliminate the confounding effects of scale, enabling comparisons across seasons and populations. The power formula helps to clarify the debate over the use of ratios, where variables may change non-isometrically. Power laws may enable the synthesis of ecological patterns sensitive to scales of space and time.

Spatial and temporal patterns of use by moose of pre-commercially thinned, naturally-regenerating stands of balsam fir in central Newfoundland.

Abstract A study of use and damage of pre-commercially thinned (PCT) forest stands containing balsam fir (Abies balsamea [L.] Mill.) by moose (Alces alces L.) in central Newfoundland was undertaken to determine how potentially conflicting resource management goals such as wood yield optimization and provision of stable moose populations could be achieved. Objectives were to measure spatial and temporal variability in damage to balsam fir due to moose habitat preferences for certain stand types and stem densities, and, secondly, to explore possibilities for manipulating PCT operations, within this context, to minimize damage. A stable moose population was achieved over 5 years of study, through the issue of licences for a management sub-area designed to coincide with on-going PCT. Good road access ensured high success for hunters in this sub-area, and this management option eventually allowed for declines in moose density and in browsing of crop trees in PCT stands. Aerial census techniques were the preferred means of determining areas of high use or high potential use; pellet group counts were only weakly correlated to measures of browsing in vegetation sample plots. Identification of localized areas of use, or of moose habitat preferences that were likely primary to the selection of PCT stands, may allow PCT operations to be planned to avoid winter moose ‘yards.’ Consideration by management should be given to locating PCT in stands like those containing black spruce, which are less frequently occupied by moose. Management of hardwood also appears to be important for reducing potential moose damage to balsam fir stands when moose densities are high.