Plastic response of fearful prey to the spatiotemporal dynamics of predator distribution.

Ecological theory predicts that the intensity of antipredator responses is dependent upon the spatiotemporal context of predation risk (the risk allocation hypothesis). However, most studies to date have been conducted over small spatial extents, and did not fully take into account gradual responses to predator proximity. We simultaneously collected spatially explicit data on predator and prey to investigate acute responses of a threatened forest ungulate, the boreal caribou (Rangifer tarandus), to the spatiotemporal dynamics of wolf (Canis lupus) distribution during spring. Movement analysis of GPS-collared individuals from both species revealed high plasticity in habitat-selection decisions of caribou. Female caribou avoided open areas and deciduous forests and moved relatively fast and toward foraging areas when wolves were closer than 2.5 km. Caribou also avoided food-rich areas only when wolves were within 1 km. Our results bridge the gap between long-term perceived risk and immediate flight responses by revealing dynamic antipredator tactics in response to predator proximity.

The influence of landscape matrix on isolated patch use by wide-ranging animals: conservation lessons for woodland caribou.

For conservation purposes, it is important to design studies that explicitly quantify responses of focal species to different land management scenarios. Here, we propose an approach that combines the influence of landscape matrices with the intrinsic attributes of remaining habitat patches on the space use behavior of woodland caribou (Rangifer tarandus caribou), a threatened subspecies of Rangifer. We sought to link characteristics of forest remnants and their surrounding environment to caribou use (i.e., occurrence and intensity). We tracked 51 females using GPS telemetry north of the Saguenay River (Québec, Canada) between 2004 and 2010 and documented their use of mature forest remnants ranging between 30 and ∼170 000 ha in a highly managed landscape. Habitat proportion and anthropogenic feature density within incremental buffer zones (from 100 to 7500 m), together with intrinsic residual forest patch characteristics, were linked to caribou GPS location occurrence and density to establish the range of influence of the surrounding matrix. We found that patch size and composition influence caribou occurrence and intensity of use within a patch. Patch size had to reach approximately 270 km(2) to attain 75% probability of use by caribou. We found that small patches (<100 km(2)) induced concentration of caribou activities that were shown to make them more vulnerable to predation and to act as ecological traps. Woodland caribou clearly need large residual forest patches, embedded in a relatively undisturbed matrix, to achieve low densities as an antipredator strategy. Our patch-based methodological approach, using GPS telemetry data, offers a new perspective of space use behavior of wide-ranging species inhabiting fragmented landscapes and allows us to highlight the impacts of large scale management. Furthermore, our study provides insights that might have important implications for effective caribou conservation and forest management.

Impacts of human disturbance on large prey species: do behavioral reactions translate to fitness consequences?

Anthropogenic disturbances have been demonstrated to affect animal behavior, distribution, and abundance, but assessment of their impacts on fitness-related traits has received little attention. We hypothesized that human activities and infrastructure cause a decrease in the individual performance of preys because of anthropogenically enhanced predation risk. We evaluated the impacts of commercial logging and road networks on the fitness of a large herbivore known to be sensitive to human disturbance: the forest-dwelling woodland caribou (Rangifer tarandus caribou). For 8 consecutive years (2004-2011) we monitored 59 individuals using GPS telemetry in the Charlevoix region of Québec, Canada. We also used Very High Frequency telemetry locations collected on 28 individuals from 1999-2000. We related habitat selection of adult caribou at various spatio-temporal scales to their probability of dying from predation, and to indices of their reproductive success and energy expenditure. The probability that adult caribou died from predation increased with the proportion of recent disturbances (including cutblocks ≤ 5 years old) in their annual home range. The respective effects of increasing paved and forestry road densities depended upon the overall road density within the home range of caribou. At a finer scale of 10 to 15 days before their death, caribou that were killed by a predator selected for recent disturbances more than individuals that survived, and avoided old mature conifer stands. The home range area of caribou increased with road density. Finally, the composition of the home range of females had no effect on their reproductive success. We show that human activities and infrastructure may influence the individual performance of large prey species in highly managed regions. We outline the need to consider the full set of impacts that human development may have on threatened animal populations, with particular emphasis on predator-prey relationships and population dynamics.

Avoidance of roads and selection for recent cutovers by threatened caribou: fitness-rewarding or maladaptive behaviour?

The impact of anthropogenic disturbance on the fitness of prey should depend on the relative effect of human activities on different trophic levels. This verification remains rare, however, especially for large animals. We investigated the functional link between habitat selection of female caribou (Rangifer tarandus) and the survival of their calves, a fitness correlate. This top-down controlled population of the threatened forest-dwelling caribou inhabits a managed forest occupied by wolves (Canis lupus) and black bears (Ursus americanus). Sixty-one per cent of calves died from bear predation within two months following their birth. Variation in habitat selection tactics among mothers resulted in different mortality risks for their calves. When calves occupied areas with few deciduous trees, they were more likely to die from predation if the local road density was high. Although caribou are typically associated with pristine forests, females selected recent cutovers without negative impact on calf survival. This selection became detrimental, however, as regeneration took place in harvested stands owing to increased bear predation. We demonstrate that human disturbance has asymmetrical consequences on the trophic levels of a food web involving multiple large mammals, which resulted in habitat selection tactics with a greater short-term fitness payoff and, therefore, with higher evolutionary opportunity.

Linking trade-offs in habitat selection with the occurrence of functional responses for moose living in two nearby study areas.

A species may modify its relative habitat use with changing availability, generating functional responses in habitat selection. Functional responses in habitat selection are expected to occur when animals experience trade-offs influencing their habitat selection, but only a few studies to date have explicitly linked functional responses to the underlying trade-offs faced by the animals. We used data from 39 female moose fitted with GPS telemetry collars in two nearby study areas in Canada to investigate if moose (1) were faced with a food/cover trade-off in habitat selection, as typically acknowledged in the literature, and (2) showed a functional response in their use of food/cover-rich habitats. We also examined how habitat selection patterns varied seasonally, and between study areas. The occurrence of functional responses varied strongly between study areas, and could not always be related to a measurable food/cover trade-off. Functional responses were observed more often in the study area where the environmental conditions were more severe (colder temperatures, higher precipitations, and lower food availability). Selection coefficients were also less variable among individuals in that study area, suggesting that severe environmental conditions may constrain individuals to a few selection tactics and promote the development of functional responses. Moose reacted to the availability of different habitat types in different seasons, reflecting the changing trade-offs faced by the animals. We found considerable behavioral differences between individuals from two adjacent study areas, and therefore recommend caution when extrapolating habitat selection results. We advocate for the wider use of functional responses to identify critical habitats for a species from a management or conservation perspective.

Influence of forage preferences and habitat use on 13C and 15N abundance in wild caribou (Rangifer tarandus caribou) and moose (Alces alces) from Canada.

Stable isotope composition (delta(13)C and delta(15)N) of moose (Alces alces) and caribou (Rangifer tarandus) hair from the boreal forest of Jacques-Cartier Park and Cote-Nord (Quebec) and arctic tundra of Queen Maud Gulf and Southampton Island (Nunavut) was investigated as an indicator of dietary preferences and habitat use. Values of delta(13)C(hair) and delta(15)N(hair) in moose were consistently lower compared to those of caribou. This is consistent with the depletion in (13)C and (15)N in the plants preferred by moose, essentially browse (shrub and tree leaves), compared to caribou forage, which included significant amounts of graminoids, lichen and fungi. The delta(13)C(hair) values of caribou differed between closed boreal forest and open-tundra ecosystems. This pattern followed that expected from the canopy effect observed in plant communities. Variation in delta(15)N(hair) values of caribou was probably linked to the effect of different climatic conditions on plant communities. This study underlines the potential of isotopic analysis for studies on diet and habitat selection within a pure C(3) plant environment.

Impact of growth form and carbohydrate reserves on tolerance to simulated deer herbivory and subsequent recovery in Liliaceae.

PREMISE OF THE STUDY: Over-browsing of the understory vegetation by white-tailed deer has been a cause of decline in many plant populations. Liliaceae are particularly sensitive, yet individual species differ in their tolerance to deer herbivory. In this paper, we examine whether differences in clonal habit, carbon allocation patterns, and phenology influence the capacity of a species to tolerate and recover from repeated herbivory. • METHODS: Flowering ramets of Clintonia borealis, Maianthemum canadense, and Trillium erectum were subjected to total defoliation for one or two springs. • KEY RESULTS: Survival was highest in the nonclonal species, T. erectum, most probably due to its very large carbohydrate reserves. Nutrient reserves were less affected than carbohydrate reserves by defoliation, confirming the importance of carbohydrate reserves for survival. However, faster recovery following episodes of defoliation was observed not in the species that sprouted the earliest, T. erectum, but in the clonal species, M. canadense, which had the smallest carbohydrate reserves but also a lower shoot to root ratio than the other clonal species, C. borealis. All plants that were defoliated for 2 years only partially recovered in terms of leaf area, plant biomass, and carbohydrate and nutrient reserves, confirming the overall sensitivity of these species to simulated deer herbivory. • CONCLUSIONS: High carbohydrate reserves and consequently low shoot to root ratios appear to increase tolerance to herbivory, whereas clonal species recover faster than nonclonal species. The role played by carbohydrates reserves suggests that these species could benefit from slightly higher light conditions in areas subjected to high deer pressure.

Population density and small-scale variation in habitat quality affect phenotypic quality in roe deer.

We tested for fine-scale spatial heterogeneity in habitat quality in a roe deer (Capreolus capreolus) population in the Chizé reserve located in western France by measuring spatial variation in the availability and plant nitrogen content of principal and preferred plant species. There were significant differences in habitat quality within the reserve: the principal food plants in spring and summer occurred more frequently in the oak woodland in the north than in the beech woodland in the south of the reserve. Within species, plants in the north had higher nitrogen contents than in the south. There was a positive spatial covariation between habitat quality, local density and fawn body weight: animal densities and fawn body weights were highest in the north, the best habitat (i.e. the habitat with more abundant food of higher quality). These results differ from those recently obtained on red deer (Cervus elaphus). We suggest that spatial organization and foraging behaviour must be accounted for when considering the effect of habitat quality on individual fitness of ungulates.

Evidence for a trade-off between growth and body reserves in northern white-tailed deer.

We contrasted patterns of growth and accumulation of body reserves in autumn between two high-density (HD) white-tailed deer populations facing winters of different severity and length. Both populations occurred in the absence of effective predators and suffered from some forage competition based on reduced body masses. A third population living at low density (LD) and confronting long and severe winters (SW) served to distinguish the influence of food competition and winter severity on growth and body reserves. We estimated body components (water, protein, fat and ash) of deer during the first half of November and compared growth patterns between sexes and regions. HD-SW males continuted growth to an older age than HD males facing short and mild winters (MW) but females of both regions reached adult body mass at the same age. LD-SW deer exhibited a growth pattern similar to that of HD-SW animals but were the heaviest and the largest, suggesting that growth patterns are related to winter harshness (or length of the growing season) and that final body size is related to forage competition in summer. Sexual dimorphism became evident at an older age in the HD-SW population than in the HD-MW population, demonstrating that winter harshness does not affect immature males and females in the same manner. Fawns from the HD-SW population had proportionally longer legs and a higher percentage of body fat. Adaptations of immature deer to long and severe winters suggest that survival during the first winter represents the most critical step in the life span of northern white-tailed deer.

Food choice by white-tailed deer in relation to protein and energy content of the diet: a field experiment.

Optimality models of food selection by herbivores assume that individuals are capable of assessing forage value, either directly through the currency used in the model or indirectly through other variables correlated with the currency. Although energy and protein are the two currencies most often used, controversy exists regarding their respective influence on food choice. Part of the debate is due to the difficulty of teasing apart these two nutrients, which are closely correlated in most natural forages. Here we offer a test of the assumption that energy and protein contents of the forage are both currencies that large mammalian herbivores can use when selecting their food. We observed feeding behavior of 47 wild white-tailed deer (Odocoileusvirginianus) during winter while individuals were presented with four experimental foods representing two levels of energy and protein (dry matter digestibility: 40-50%; crude protein: 12-16%). Using experimental foods allowed us to separate the influences of energy and protein and clearly distinguish between the roles of these two nutrients. Deer discriminated between foods through partial selection, and selected diets higher in energy but lower in protein. The observed choices appeared consistent with physiological needs of deer wintering at the study site, where digestible energy was in short supply in the natural environment while protein was probably not. Results are in good agreement with recent findings on domesticated ruminants. They support a basic assumption of optimality models of food selection that use energy and/or protein as a currency, although the physiological mechanisms behind the food selection process remain unclear. We urge students of food selection by herbivores to replicate our experiment with other foods and/or in other circumstances before more general conclusions are drawn.