Sandra Hamel

Annual variations in environmental conditions can strongly affect demographic rates of wild populations, such as survival and recruitment. These effects are likely to be exacerbated in highly seasonal environments and in species facing substantial energetic needs during specific seasons. In migratory mammals, for instance, females must contend with the energy expenditures required for long‐distance travel as well as those needed to complete gestation. Little is known, however, about the environmental factors influencing recruitment in species exhibiting long‐distance migrations. We aimed to fill this gap by evaluating the effect of environmental conditions from pre‐gestation to weaning on fall recruitment of two migratory caribou Rangifer tarandus herds followed over nearly three decades in northeastern Canada. Recruitment decreased with high precipitation experienced by adult females around estrus in previous fall and during gestation in winter, as well as with warm temperatures during gestation in winter and at calving. These environmental conditions experienced by both populations were positively correlated, suggesting they could increase overall recruitment synchrony between nearby populations. We found no evidence for an effect of conditions experienced after birth, suggesting that environmental conditions encountered from conception to calving are likely the strongest determinants of recruitment in migratory caribou. Results of this population‐level analysis highlight the importance of female condition throughout gestation with maternal allocation in fetal growth and the newborn calf playing a major role in recruitment. Synchrony observed in recruitment between herds also underlines the importance of considering multiple populations facing similar environmental conditions in conservation strategies as they may exhibit simultaneous fluctuations in abundance.

Environmental conditions in early life can generate long‐term individual differences in life‐history traits such as survival and reproduction. Early‐life conditions can challenge developing individuals through distinct environmental mechanisms. Each mechanism can induce long‐term consequences, potentially leading to cohort effects in which individuals born in different years exhibit persistent differences in life‐history traits. In ungulates, early life spans three sensitive periods—gestation, preweaning, and postweaning—during which distinct environmental mechanisms may exert long‐term effects. Most studies, however, have examined only a single period or mechanism, leaving the combined effects of multiple mechanisms across development largely untested, despite evidence that these effects are often multifactorial. Benefiting from over 20 years of life‐history data on migratory caribou ( Rangifer tarandus ) from the Rivière‐aux‐Feuilles and Rivière‐George herds in northern Québec and Labrador (Canada), we investigated how three environmental mechanisms—environmental energetic constraints, resource availability, and competition—during gestation, preweaning, and postweaning influenced life‐history traits. We hypothesized that harsh conditions during gestation and preweaning would most strongly reduce early‐life body condition, survival to adult age, and longevity. We first performed a confirmatory path analysis to evaluate effects on early‐life body condition and survival to adult age, followed by a time‐to‐event analysis to assess differences in longevity. Our results indicate that high environmental energetic constraints during gestation and limiting resource availability in late gestation and early preweaning reduced early‐life body condition and survival to adult age. Among individuals surviving to adulthood, early‐life competition also strongly reduced longevity. Overall, effects on life‐history traits were associated with environmental conditions during gestation or early preweaning and stemming from multiple environmental mechanisms. These findings underscore the importance of gestational and early postnatal environments in shaping life‐history traits. These results also demonstrate how a multifactor, multi‐period approach provides a more complete understanding of how early‐life conditions determine individual fitness, with strong implications for population dynamics.

Annual variations in environmental conditions can strongly affect vital rates such as survival and recruitment. These effects are likely to be exacerbated in highly seasonal environments and in species facing substantial energetic needs during specific seasons. For instance, pregnant migratory females must balance energy expenditure between long-distance travel and gestation. Little is known, however, on the environmental factors influencing recruitment in species exhibiting long-distance migrations. We aimed to fill this gap by evaluating the effect of environmental conditions from pre-gestation to weaning on fall recruitment of two migratory caribou (Rangifer tarandus) herds followed for over 35 years in northeastern Canada. Fall recruitment decreased with high precipitation experienced by adult females around estrus in previous fall (12% [95% confidence interval: 1-22]) and during gestation in winter (13% [3-21]), as well as with warm temperature (13% [3-23]) during gestation in winter and at calving (12% [2-21]). These environmental conditions experienced by both populations were positively correlated, suggesting these parameters could increase overall recruitment synchrony between nearby populations. We found no support for an effect of conditions experienced after birth, demonstrating that environmental conditions encountered from conception to calving are the strongest determinants of recruitment in migratory caribou. Our results highlight the importance of female condition throughout gestation with maternal allocation in fetal growth and newborn calf playing a major role in recruitment. Synchrony observed in recruitment between herds also underlines the importance of considering multiple populations facing similar environmental conditions in conservation strategies as they may exhibit simultaneous fluctuations.

High‐latitude environments are characterised by strong seasonality, with resident animals experiencing a very short plant‐growing season for reproduction and acquisition of resources before the long and demanding winter. These seasonal fluctuations in food availability are likely to affect density‐dependent processes, with density‐dependent food limitation expected to be stronger outside the plant‐growing season. Density dependence and environmental variability can have both direct and indirect effects on reproductive success through their influence on important indicators of individual quality, such as body mass. Untangling the direct and indirect effects of environmental factors and population density on life‐history tactics is fundamental for understanding population and food‐web dynamics. We developed a mechanistic path model to quantify the relative importance of direct and indirect effects of density dependence and environmental variability on body mass and reproductive success of female reindeer. Long‐term individual measurements before and after lactation allowed quantifying simultaneously the direct negative effect of reproductive success on autumn body mass and the strong positive seasonal covariation among the individuals' body mass measurements. This emphasises the co‐occurrence of a cost of reproduction and individual heterogeneity. We show that the estimated impact of density dependence on female body mass at the end of the summer is only 25% of the impact of density dependence during winter, as failed reproduction induced by low spring body mass leads to a large compensatory growth over summer. While such a pattern is expected, our estimates provide a unique and robust quantification of its importance. This result challenges the use of body mass data of adult individuals harvested in autumn when studying temperate large herbivores, as density dependence during winter and compensatory adjustments of reproductive effort may not be revealed without considering body mass both before and after lactation.

Individual heterogeneity shapes ecoevolutionary processes at multiple scales. Yet, the scarcity of long-term life-history data and limitations in classic statistical tools hinder our capacity to uncover and understand individual heterogeneity in wildlife populations. Here, we apply an underused multivariate statistical method to uncover four heterogenous life-history trajectories in wild female bighorn sheep ( Ovis canadensis ). Remarkably, these trajectories had remained unobserved in the population despite nearly five decades of monitoring. Our results indicate substantial among-trajectory heterogeneity in growth, senescence, life history trade-offs, fitness, and contributions to population growth. Some trajectories suggest the presence of life history trade-offs while others include silver spoon effects, leading to heterogenous life-history outputs. Then, we show that mother identity and year of birth are relatively good predictors of heterogeneity, indicating that individual trajectories could be largely set during early life. Critically, our results demonstrate that heterogeneity in life-history trajectories can be inconspicuous, yet substantial and structured across multiple traits within a population. Uncovering and understanding this heterogeneity in other wild populations will be key to advancing our knowledge of ecoevolutionary processes across populations and species.

Spatial variations in food availability may influence life‐history traits of wildlife species, particularly in capital‐breeding species that store energy when food is widely available and catabolize it during energy‐intensive reproductive periods. The reproductive success of capital breeders is thus highly dependent on the accumulation of fat reserves. Reproductive success may also improve with access to alternative food resources provided by environments with strong human footprint and anthropogenic disturbances, but these environments may also increase mortality risks of wildlife. We performed a systematic review to extract reproduction and survival traits reported in studies on the American black bear (Ursus americanus), a capital breeder. Based on 94 studies widely distributed across North America, we conducted meta‐regression analyses to assess whether interpopulation variation in age at primiparity, litter size of cubs, annual cub survival, and annual survival of adult females were associated with environmental conditions, that is, habitat quality, habitat productivity, and anthropogenic disturbances. We found that mean age at primiparity decreased from around 5 to 4 years old in areas with the highest habitat quality and productivity as well as the highest human population densities compared with those with poor habitat quality and productivity and low human population densities. Mean litter size increased by approximately 13% (from 2 to 2.25 cubs per litter) in areas with the highest compared with the lowest proportion of deciduous forest, while cub survival increased by about 13% (from 60% to 73%) in areas with the highest compared with the lowest coverage of agricultural crops. Adult female survival decreased from 92% to 85% in areas where hunting was allowed. These results provide new insights into the factors associated with variations in reproductive success and survival across populations of a widely distributed species, demonstrating the impact of both natural and anthropogenic factors. Our study highlights the necessity of considering the ongoing changes in the distribution and growth of potential food resources, as well as the growing encroachment of humans into wildlife habitats, when planning management and conservation actions at the scale of a species distribution range.

Vigilance allows animals to quickly detect threats from conspecifics and predators to avoid or minimize costly encounters. Time spent vigilant is usually traded‐off against other fitness‐enhancing activities, such that fitness returns are expected when allocation to vigilance increases. We assessed the proximate factors influencing vigilance and investigated whether vigilance correlates with fitness in wild mountain goats. We first studied which extrinsic and intrinsic factors influenced alert duration and frequency using focal observations recorded over 12 years on individually‐marked adult females. We found that females increased vigilance in forested areas compared with open areas and were less vigilant when they were surrounded by conspecific neighbours. Reproductive females were more frequently vigilant and for longer periods compared with females without offspring. Mothers also tended to perform longer alerts when their offspring was > 10 m away than at shorter distances, suggesting that variation in offspring's vulnerability to predation influences mother's vigilance. Thus, predation risk and offspring vulnerability were the main mechanisms driving variation in vigilance. To assess fitness returns, we then used a joint modelling framework to estimate the latent correlations at the individual level among vigilance traits (alert duration, alert frequency, and total time spent vigilant) and fitness components (adult female survival and offspring survival) while accounting for the drivers observed to influence vigilance. Contrary to expectations, we found no evidence that vigilance is associated with fitness returns, with only some traits being at best weakly positively correlated with survival of offspring and adult females. This might arise because vigilance incurs costs that outweighs its potential benefits, or because vigilance metrics are not repeatable due to their high plasticity, challenging the commonly assumed positive relationship between vigilance and fitness.

Climate change disproportionately affects northern and alpine environments, with faster rates of warming than the global average. Because alpine and northern species are particularly well adapted to cool temperatures, most species must modify their behavior when temperatures exceed a critical threshold. Evaluating how temperature increases affect species inhabiting northern and alpine environments is therefore essential to understand the effects of projected climate change on these ecosystems. We analyzed the influence of temperature on the activity patterns and habitat selection of four populations of a cold-adapted, mountain specialist, the mountain goat (Oreamnos americanus). We collected GPS location and activity sensor data during 2010–2019 from 223 mountain goats from two distinct ecotypes: coastal and continental. Using a resource selection modeling approach, we determined that mountain goats of both ecotypes decreased selection for alpine meadows when temperatures increased. Reduced selection for open, forage rich habitat was associated with increased selection for habitat dominated by snow/ice patches in coastal areas, and by forests in continental sites. Mountain goats in continental environments selected higher elevation habitats only when temperature increased, whereas goats in coastal environments selected higher elevation habitat at all temperatures. Mountain goats of both ecotypes reduced the proportion of time spent active when temperatures increased during the middle of the day. Our study reveals that mountain goats use diverse tactics to mitigate thermal stress, and that these tactics vary between ecotypes, highlighting the need for considering adaptation to specific environments within a species when assessing climate change impacts on populations.