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Personne :
Hamel, Sandra

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Hamel

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Sandra

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Université Laval. Département de biologie

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ncf11855917

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Voici les éléments 1 - 10 sur 14
  • PublicationAccès 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.
  • PublicationRestreint
    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.
  • PublicationRestreint
    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.
  • PublicationAccès 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.
  • PublicationRestreint
    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.
  • PublicationRestreint
    Habitat use patterns in relation to escape terrain : are alpine ungulate females trading-off better foraging sites for safety?
    (Canadian Science Publishing, 2007-10-02) Hamel, Sandra; Côté, Steeve D.
    Predation risk often forces prey to trade off good foraging sites for safety, and compromises are expected to be greater in females with vulnerable offspring than in barren females. To determine whether adult females of large herbivores traded off forage for safety, we assessed habitat use and estimated vegetation abundance and quality in relation to distance to escape terrain in marked mountain goats (Oreamnos americanus de Blainville, 1816). We found that all females spent more time foraging near escape terrain than away from them. Females with young foraged on average 20 m closer to escape terrain than barren females in June, a time when offspring were particularly vulnerable to predation. Plant biomass did not vary with distance to escape terrain in June, but was lower closer than away from escape terrain during all other months. The abundance of forbs and shrubs increased with distance to escape terrain, but their quality did not vary. For grasses and sedges, plant digestible content decreased closer to escape terrain, but interestingly proteins increased. Our results suggest that females traded off forage abundance, and to a lesser extent forage quality, for safety. Compared with barren females, females with offspring may face a trade-off in plant digestible content by foraging in safer areas than barren females.
  • PublicationRestreint
    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.
  • PublicationAccès libre
    Influence of early reproductive success on longevity and late reproductive success in an alpine ungulate
    (2017-03-20) Hamel, Sandra; Panagakis, Andrea; Côté, Steeve D.
    The life-history theories of aging predict lifetime trade-offs between early reproductive allocation and late-life survival, reproduction, or both components of fitness. Recent studies in wild populations have found evidence for these early-late life trade-offs, but rarely have they been found across multiple traits while exploring the additional effects of variation in environmental conditions and individual quality. Benefiting from longitudinal data on adult female mountain goats (Oreamnos americanus), we investigated the influence of age at first reproduction (AFR) and early reproductive success (ERS) on longevity, late reproductive success, and senescence rates while accounting for the influence of natal environmental conditions and individual quality. Contrary to predictions, we did not find evidence for early-late life trade-offs. Instead, an earlier AFR and a greater ERS had positive but weak direct effects on late reproductive success. Natal population density, however, was the strongest determinant of all life-history traits, having a direct negative effect on female longevity, late reproductive success, AFR, and ERS. Although natal density reduced the probability of annual reproduction and annual survival during adulthood, higher allocation to reproduction in early life and poorer natal conditions did not lead to accelerated rates of senescence during adulthood. The results of this investigation provide an integrated picture of early-late life trade-offs, underscoring the importance of accounting for environmental conditions because of their potentially strong implications for population dynamics.
  • PublicationAccès libre
    Les compromis à court et à long terme associés à la reproduction chez les ongulés femelles : l'exemple de la chèvre de montagne
    (2008) Hamel, Sandra; Côté, Steeve D.
    Les espèces longévives ont développé une stratégie de reproduction conservatrice où les individus produisent peu de jeunes annuellement et déploient leur effort reproducteur sur plusieurs années. Ainsi, plusieurs facteurs propres à l'individu, tout comme de nombreuses variables environnementales, peuvent grandement affecter la reproduction annuelle, entraînant des effets directs sur l'aptitude phénotypique individuelle et des effets indirects sur la dynamique des populations. En utilisant des données longitudinales sur des populations sauvages d'individus marqués, particulièrement la chèvre de montagne (Oreanmos americanus), ma thèse vise à évaluer les compromis à court et à long terme associés à la reproduction chez les ongulés femelles, tout en considérant les variations individuelles et les effets environnementaux. A court terme, mes résultats montrent que les femelles modifient leur comportement d'approvisionnement lorsqu'elles ont un jeune afin d'augmenter leur prise alimentaire et de compenser pour les coûts énergétiques de la lactation. Néanmoins, les jeunes femelles font face à un compromis important entre la croissance et la lactation. A plus long terme, les femelles qui produisent un jeune ont une plus faible probabilité de produire un jeune à nouveau, et que ce jeune survive jusqu'à 1 an, que les femelles qui ne se sont pas reproduites. Ces coûts de la reproduction sont plus élevés pour les femelles de plus faible qualité et plus jeunes que pour les femelles de plus haute qualité et plus vieilles. Les coûts s'intensifient également avec l'augmentation de la densité de population et la détérioration des conditions environnementales. A plus grande échelle, mes résultats montrent que les variations individuelles de la survie et de la reproduction influencent le rendement des populations, et que ce sont les femelles âgées qui ont le plus grand impact sur la productivité des populations. Ainsi, ma thèse permet d'illustrer les compromis réalisés par les femelles au cours de la reproduction, et ce à court et à long terme. Puisque ces compromis entraînent des coûts sur l'aptitude phénotypique et que ces coûts varient selon la qualité des individus, ces connaissances sont essentielles pour comprendre les variables sur lesquelles agissent les pressions de sélection et pour expliquer les variations dans le rendement des populations.
  • PublicationRestreint
    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.