Personne :
Hamel, Sandra

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Structures organisationnelles
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Université Laval. Département de biologie
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Résultats de recherche

Voici les éléments 1 - 10 sur 13
  • Publication
    Population dynamics and harvest potential of mountain goat herds in Alberta
    (Wildlife Society, 2010-12-13) Hamel, Sandra; Festa-Bianchet, Marco; Smith, Kirby G.; Côté, Steeve D.
    The understanding of population dynamics is a central issue for managing large mammals. Modeling has allowed population ecologists to increase their knowledge about complex systems and better predict population responses to diverse perturbations. Mountain goats (Oreamnos americanus) appear sensitive to harvest, but the relative influence of survival and reproductive rates on their population dynamics are not well understood. Using longitudinal data on age- and sex-specific survival and reproduction from a marked mountain goat population in Alberta, Canada, we built a stage-class matrix model to predict short-term numerical changes for 11 other goat populations in Alberta for which the only data available were from annual aerial surveys. Overall, the model provided an acceptable fit to changes in population size for 8 of 12 populations. Temporal trends in population size were underestimated in 2 populations and overestimated in another 2, suggesting that these populations had different vital rates than those of the intensively studied population. Sensitivity analyses revealed that the survival of mature females (aged 5 yr and older) had the greatest elasticity for population growth. Modeled management scenarios indicated that nonselective yearly harvest rates above 1% of goats aged 2 years and older were not sustainable over the short-term for some populations. The simulations also revealed that small (n = 25) and medium-size (n = 50) populations, which correspond to most goat populations in Alberta, had high extinction risk (18 to 82% over 40 years), even in the absence of harvest. Our results confirm that mountain goat populations are very sensitive to harvest, indicate that wildlife managers should prevent female harvest, and suggest that although a high demand for goat hunting exists in Alberta, most populations in this province—and probably small populations elsewhere—cannot withstand exploitation.
  • Publication
    Accès libre
    Maternal defensive behavior of mountain goats against predation by golden eagles
    (2009-04-01) Hamel, Sandra; Côté, Steeve D.
    Maternal defensive behavior against predators may appear risky but is common in many species. Herein we describe maternal defensive behavior of mountain goats (Oreamnos americanus) against Golden Eagle (Aquila chrysaetos) predatory attempts. We found that Golden Eagles attacked goats in 1.9% of sightings (n = 311 sightings of active Golden Eagles over 12 years) but were never successful. Mothers always defended their young against Golden Eagle attacks. Predation by Golden Eagles on young-of-the-year appears low for most ungulate species, including mountain goats. The benefits of defending offspring against eagles are likely high in ungulates, and we would therefore expect selection to favor maternal defensive behavior.
  • Publication
    Spring normalized difference vegetation index (NDVI) predicts annual variation in timing of peak faecal crude protein in mountain ungulates
    (British Ecological Society, 2009-04-28) Hamel, Sandra; Garel, Mathieu; Festa-Bianchet, Marco; Côté, Steeve D.; Gaillard, Jean-Michel
    1 In recent years, the Normalized Difference Vegetation Index (NDVI) has been used to assess the relationships between habitat quality and animal life-history traits. Since numerous ecological studies now use NDVI rather than perform direct vegetation assessments, field validations are essential to provide confidence in the biological significance of NDVI estimates. While some studies have compared NDVI with plant biomass, very few examined the relationship between NDVI and changes in vegetation quality. 2 Using data from two long-term studies of alpine ungulates, we assessed the relationship between two NDVI indices and the date of peak in faecal crude protein (FCP), which represents temporal variability in the availability of high-quality vegetation. We also evaluated if NDVI data could predict annual variation in the timing of spring green-up. 3 In both populations, integrated NDVI in June was negatively correlated with the date of the peak in FCP, indicating that high integrated NDVI values corresponded to early springs in alpine habitats. Maximum NDVI increase during spring green-up was positively correlated with the timing of peak FCP, illustrating that rapid increases in NDVI represented delayed springs. 4 Predicted values of date of peak FCP estimated each year from NDVI data satisfactorily fitted observed values, and prediction intervals included all observed values. These results suggest that NDVI can reliably predict variation over years in the timing of spring. 5 Synthesis and applications. Our long-term studies demonstrate that a multi-year time series of Normalized Difference Vegetation Index (NDVI) can reliably measure yearly changes in the timing of the availability of high-quality vegetation for temperate herbivores. This finding therefore supports the use of NDVI as a proxy for vegetation attributes in population ecology and wildlife management studies.
  • Publication
    Ecological and evolutionary effects of selective harvest of non-lactating female ungulates
    (British Ecological Society, 2017-01-16) Rughetti, Marco; Hamel, Sandra; Festa Bianchet, Marco; Côté, Steeve D.
    Female ungulates are often selectively harvested according to their reproductive status. Because ungulate population growth depends heavily on adult female survival, it is crucial to understand the effects of this selective harvest. Recent studies revealed persistent individual differences in female reproductive potential, with a positive correlation of reproductive success over consecutive years. If current reproduction is correlated with lifetime reproductive success, then selective harvest of non-lactating females should remove individuals of low reproductive potential, with lower impact on population growth than random harvest. If lifetime reproductive success has a genetic basis, selective harvest may also increase the proportion of successful females. We used an individual-based model to understand the short-term effects of harvest intensity and hunter selectivity on population dynamics, accounting for both heterogeneity in reproductive potential and orphan survival. We also explored the long-term effect of harvest as a selective pressure on female heterogeneity. Selective harvest of non-lactating females reduced survival to primiparity compared to random harvest, because of high harvest rates of pre-reproductive females. After primiparity, however, females of higher reproductive potential had higher survival under selective than random harvest. Therefore, the overall effect on population dynamics depends on a trade-off between a high harvest of pre-reproductive females and a reduced harvest of reproductive females with high reproductive potential. Female heterogeneity and the length of the pre-reproductive period affected this trade-off. Over the short term, high heterogeneity in reproductive potential of pre-reproductive females made selective harvest the most effective strategy to maintain a high population growth rate. With low heterogeneity and little effects of orphaning on juvenile mortality, however, random harvest had a lower impact on population growth than selective harvest. Over the long term, selective female harvest may increase the proportion of successful reproducers in the population. Synthesis and applications. Selective harvests of non-lactating females appear justified only if female heterogeneity in reproductive potential and/or orphan mortality are very high. Because pre-reproductive females will be subject to intense harvest, selective harvest may reduce population growth rate compared to random harvest in species with late primiparity, especially if most pre-reproductive female normally survive to primiparity. When heterogeneity in reproductive potential and orphan mortality are low, random female harvest appears preferable to selective harvest.
  • Publication
    Accès libre
    Cohort variation in individual body mass dissipates with age in large herbivores
    (Duke University Press, 2016-11-01) Hamel, Sandra; Gaillard, Jean-Michel; Yoccoz, Nigel Gilles; Côté, Steeve D.; Albon, Steve; Craine, Joseph; Festa-Bianchet, Marco; Garel, Mathieu; Lee, Phyllis C.; Moss, Cynthia; Nussey, Dan; Stien, Audun; Tveraa, Torkild; Pelletier, F.
    Environmental conditions experienced during early growth and development markedly shape phenotypic traits. Consequently, individuals of the same cohort may show similar life-history tactics throughout life. Conditions experienced later in life, however, could fine-tune these initial differences, either increasing (cumulative effect) or decreasing (compensatory effect) the magnitude of cohort variation with increasing age. Our novel comparative analysis that quantifies cohort variation in individual body size trajectories shows that initial cohort variation dissipates throughout life, and that lifetime patterns change both across species with different paces of life and between sexes. We used longitudinal data on body size (mostly assessed using mass) from 11 populations of large herbivores spread along the “slow-fast” continuum of life histories. We first quantified cohort variation using mixture models to identify clusters of cohorts with similar initial size. We identified clear cohort clusters in all species except the one with the slowest pace of life, revealing that variation in early size is structured among cohorts and highlighting typological differences among cohorts. Growth trajectories differed among cohort clusters, highlighting how early size is a fundamental determinant of lifetime growth patterns. In all species, among-cohort variation in size peaked at the start of life, then quickly decreased with age and stabilized around mid-life. Cohort variation was lower in species with a slower than a faster pace of life, and vanished at prime age in species with the slowest pace of life. After accounting for viability selection, compensatory/catch-up growth in early life explained much of the decrease in cohort variation. Females showed less phenotypic variability and stronger compensatory/catch-up growth than males early in life, whereas males showed more progressive changes throughout life. These results confirm that stronger selective pressures for rapid growth make males more vulnerable to poor environmental conditions early in life and less able to recover after a poor start. Our comparative analysis illustrates how variability in growth changes over time in closely related species that span a wide range on the slow-fast continuum, the main axis of variation in life-history strategies of vertebrates.
  • Publication
    Fluctuating optimum and temporally variable selection on breeding date in birds and mammals
    (National Academy of Sciences of the United States of America, 2020-11-30) Hamel, Sandra; Villemereuil, Pierre de; Festa-Bianchet, Marco; Charmantier, Anne; Côté, Steeve D.; Arlt, Debora; Bize, Pierre; Brekke, Patricia; Brouwer, Lyanne; Cockburn, Andrew; Dobson, F. Stephen; Evans, Simon R.; Gamelon, Marlène; Hegelbach, Johann; Jerstad, Kurt; Kempenaers, B. (Bart); Kruuk, Loeske E. B.; Kumpula, Jouko; Kvalnes, Thomas; McAdam, Andrew G.; McFarlane, S. Eryn; Morrissey, Michael B.; Pärt, Tomas; Pemberton, Josephine M.; Qvarnström, Anna; Wiggo Røstad, Ole; Schroeder, Julia; Senar, Juan Carlos; Sheldon, Ben C.; Pol, Martijn van de; Visser, Marcel E.; Tufto, Jarle; Chevin, Luis-Miguel
    Temporal variation in natural selection is predicted to strongly impact the evolution and demography of natural populations, with consequences for the rate of adaptation, evolution of plasticity, and extinction risk. Most of the theory underlying these predictions assumes a moving optimum phenotype, with predictions expressed in terms of the temporal variance and autocorrelation of this optimum. However, empirical studies seldom estimate patterns of fluctuations of an optimum phenotype, precluding further progress in connecting theory with observations. To bridge this gap, we assess the evidence for temporal variation in selection on breeding date by modeling a fitness function with a fluctuating optimum, across 39 populations of 21 wild animals, one of the largest compilations of long-term datasets with individual measurements of trait and fitness components. We find compelling evidence for fluctuations in the fitness function, causing temporal variation in the magnitude, but not the direction of selection. However, fluctuations of the optimum phenotype need not directly translate into variation in selection gradients, because their impact can be buffered by partial tracking of the optimum by the mean phenotype. Analyzing individuals that reproduce in consecutive years, we find that plastic changes track movements of the optimum phenotype across years, especially in bird species, reducing temporal variation in directional selection. This suggests that phenological plasticity has evolved to cope with fluctuations in the optimum, despite their currently modest contribution to variation in selection.
  • Publication
    Offspring sex in mountain goat varies with adult sex ratio but only for mothers in good condition
    (Springer, 2015-11-04) Hamel, Sandra; Festa-Bianchet, Marco; Côté, Steeve D.
    Studies of mammals have often produced results inconsistent with theories predicting adaptive sex-ratio manipulation. Some apparently strong trends weaken or disappear over time, suggesting that multiple variables affect sex ratio and that their relative importance may change over time. Mountain goats are sexually dimorphic ungulates that satisfy all the assumptions of the Trivers-Willard hypothesis. Therefore, females able to provide high levels of maternal care are expected to produce an excess of sons. An earlier study found that older females, that are larger and dominant, produced more sons than did younger females, which are smaller and subordinate. Here, we show that, as sample size tripled, that trend disappeared. A large-scale climate index, reproductive status at conception, and population density had no consistent effects on offspring sex ratio. A composite measure of female condition at conception revealed that offspring sex ratio varied with adult sex ratio, as predicted by the homeostatic hypothesis, but only for mothers in good condition at conception. These females were dominant, heavier, and older. Their probability of producing a son decreased from about 80 to 20 % as the adult sex ratio became more male-biased. For mothers with a low condition index, however, adult sex ratio had no effect on offspring sex ratio. Our research suggests that offspring sex ratio is affected by complex interactions between individual condition and other variables, whose importance may vary over time and can only be elucidated by long-term studies.
  • Publication
    Trade-offs in activity budget in an alpine ungulate: contrasting lactating and non-lactating females
    (Elsevier, 2007-11-19) Hamel, Sandra; Côté, Steeve D.
    Optimal time allocation to foraging behaviour may be constrained by intrinsic and extrinsic factors forcing animals to adopt compromises to meet their daily energetic needs. Our goal was to assess the influence of individual characteristics and extrinsic factors on the activity budget of marked adult female mountain goats, Oreamnos americanus. As lactation entails important energetic costs, we specifically aimed at contrasting activity budgets of lactating and nonlactating females. We determined female activity budgets using 10-min interval scan sampling between 2002 and 2005. Lactating females, females raising sons and females that were subordinate for their age spent more time foraging than nonlactating females, females raising daughters and dominant females, respectively. Although foraging is typically incompatible with scanning, increased time spent foraging was mainly performed at the expense of time spent lying rather than time spent in vigilance. Lactating females also increased time spent ruminating while lying compared with nonlactating females. All females traded lying time for increased foraging and ruminating times in early and late summer. Females spent less time foraging on warm days, and foraged more at dusk than during the rest of the day. Age and body mass did not influence female activity budgets. Our results indicate that lactating females partly compensated for the costs of lactation by trading lying for foraging time, and reorganized lying time to increase the proportion of time spent ruminating. This study emphasizes the fundamental behavioural trade-offs that female mammals must face to meet their daily energetic requirements and allows a better understanding of how these compromises vary through the lactation period.
  • Publication
    Accès libre
    Individual quality, early-life conditions, and reproductive success in contrasted populations of large herbivores
    (Brooklyn Botanical Garden, 2009-07-01) Hamel, Sandra; Gaillard, Jean-Michel; Festa-Bianchet, Marco; Côté, Steeve D.
    Variations among individuals in phenotypic quality and fitness often confound analyses of life-history strategies assessed at the population level. We used detailed long-term data from three populations of large herbivores with generation times ranging from four to nine years to quantify heterogeneity in individual quality among females, and to assess its influence on mean annual reproductive success over the lifetime (MRS). We also determined how environmental conditions in early life shaped individual quality and tested A. Lomnicki's hypothesis that variance in individual quality should increase when environmental conditions deteriorate. Using multivariate analyses (PCA), we identified one (in sheep and deer) or two (in goats) covariations among life-history traits (longevity, success in the last breeding opportunity, adult mass, and social rank) as indexes of individual quality that positively influenced MRS of females. Individual quality was reduced by unfavorable weather, low resource availability, and high population density in the year of birth. Early-life conditions accounted for 35–55% of variation in individual quality. In roe deer, we found greater variance in individual quality for cohorts born under unfavorable conditions as opposed to favorable ones, but the opposite was found in bighorn sheep and mountain goats. Our results demonstrate that heterogeneity in female quality can originate from environmental conditions in early life and can markedly influence the fitness of females in species located at different positions along the slow–fast continuum of life-history strategies.
  • Publication
    Individual variation in reproductive costs of reproduction : high quality females always do better
    (University Press, 2008-08-12) Hamel, Sandra; Festa-Bianchet, Marco; Gaillard, Jean-Michel; Côté, Steeve D.
    1 Although life-history theory predicts substantial costs of reproduction, individuals often show positive correlations among life-history traits, rather than trade-offs. The apparent absence of reproductive costs may result from heterogeneity in individual quality. 2 Using detailed longitudinal data from three contrasted ungulate populations (mountain goats, Oreamnos americanus; bighorn sheep, Ovis canadensis; and roe deer, Capreolus capreolus), we assessed how individual quality affects the probability of detecting a cost of current reproduction on future reproduction for females. We used a composite measure of individual quality based on variations in longevity (all species), success in the last breeding opportunity before death (goats and sheep), adult mass (all species), and social rank (goats only). 3 In all species, high-quality females consistently had a higher probability of reproduction, irrespective of previous reproductive status. In mountain goats, we detected a cost of reproduction only after accounting for differences in individual quality. Only low-quality female goats were less likely to reproduce following years of breeding than of nonbreeding. Offspring survival was lower in bighorn ewes following years of successful breeding than after years when no lamb was produced, but only for low-quality females, suggesting that a cost of reproduction only occurred for low-quality females. 4 Because costs of reproduction differ among females, studies of life-history evolution must account for heterogeneity in individual quality.