Effets des débris ligneux grossiers sur les micromammifères à différentes échelles spatiales en pessières à mousses aménagées du nord du Québec

Le bois mort constitue un attribut structural important du sol forestier et un nombre croissant d'études montrent qu'il est primordial pour un vaste éventail d'espèces végétales et animales et pour le recyclage des nutriments. Pourtant, certaines opérations forestières, telles que la coupe totale et les coupes avec protection de la régénération et des sols (CPRS), réduisent la quantité de débris ligneux grossiers (DLG) au sol et continuent d'être employées de manière extensive au Québec et ailleurs en Amérique du Nord. L'effet des DLG sur les micromammifères en forêt boréale aménagée est, par conséquent, méconnu dans les forêts récoltées mais il est possible que le bois mort joue un rôle important dans le maintien de leurs populations. Cette étude a pour but de déterminer les effets des DLG sur les micromammifères dans les forêts de pessières à mousses aménagées de l'ouest du Québec et ce, à plusieurs échelles spatiales. Nous supposons d'abord que (1) les micromammifères sont dépendants de la distribution des DLG, principalement ceux qui présentent un stade de dégradation avancée. Nous supposons également que (2) l'effet des DLG est important dans tous les traitements forestiers car cette ressource offre plusieurs avantages pour les micromammifères. Enfin, nous supposons que (3) les relations entre les micromammifères et les DLG seront détectées principalement à fine échelle car l'utilisation des ressources se fait d'abord au niveau de l'individu. À l'aide d'un système de piégeage structuré de façon spatiotemporelle, nous avons analysé l'abondance des micromammifères à fine échelle (50 m) et à l'échelle du peuplement forestier (300 m). La fiabilité des identifications des spécimens capturés a été assurée grâce au développement de deux clés d'identification. Ces clés ont été construites en comparant les identifications faites avec tous les critères morphologiques (identification considérée certaine) à celles faites selon les critères accessibles lorsque les spécimens sont vivants ou victimes de prédation (restes osseux). Nous avons analysé la fréquence de capture des micromammifères à l'aide de modèles linéaires généralisés mixtes où le site était l'effet aléatoire. Nous avons sélectionné les modèles les plus parcimonieux et avons procédé à l'aide d'inférence multimodèles pour chaque espèce afin de déterminer les effets du bois mort et des coupes. Les campagnols à dos roux de Gapper (Myodes gapperi), les campagnols des champs (Microtus pennsylvanicus), les campagnols-lemmings de Cooper (Synaptomys cooperi), les souris sylvestres (Peromyscus maniculatus) et les musaraignes cendrées (Sorex cinereus) ont tous répondu de façon positive aux DLG de façon spécifique. Selon les prédictions des modèles, les parcelles de coupes partielles munies d'un grand volume de DLG dégradés (11,4 m3 par 0,03 ha) présentent une abondance de campagnols à dos roux de Gapper similaires aux forêts matures peu perturbées. Les DLG dégradés ont aussi été utilisés par les campagnols-lemmings de Cooper et les musaraignes cendrées dans les coupes totales. À la lumière de nos résultats, de grands volumes de DLG dégradés ont le potentiel d'atténuer les impacts négatifs liés à la récolte des arbres matures. Nous suggérons d'assurer la présence de grands volumes de DLG dégradés après coupe afin de maintenir de fortes abondances de micromammifères, principalement ceux associés aux vieilles forêts. De plus, l'emploi des coupes partielles qui maintiennent une proportion substantielle du couvert forestier (30%) assurerait un apport continu de DLG.\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : micromammifères, forêt boréale, coupe partielle, débris ligneux grossiers, clé d'identification

Effets directs et indirects de la prédation sur les lemmings dans l'Arctique canadien

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2016-2017Les populations caractérisées par des fluctuations cycliques ont fasciné et continuent de générer un grand intérêt chez la communauté scientifique en raison de la complexité des facteurs de régulation qui en sont responsables. Plusieurs hypothèses ont été proposées pour expliquer ces fluctuations cycliques mais aucun consensus n’a encore été atteint malgré près de 100 ans de recherche. La disponibilité de la nourriture et les effets sociaux (e.g. interactions compétitives) ont été proposés comme facteurs responsables de cycles de certaines espèces. Toutefois, la prédation est probablement le facteur le plus susceptible de causer des fluctuations cycliques chez les populations fauniques en raison de son effet dépendant de la densité avec délai. Un tandem circulaire de raréfaction et densification des prédateurs et des proies par des effets directs (i.e. mortalités) seraient à l’origine des cycles d’abondance. De plus, de récentes études montrent que les effets indirects (comme le stress) de la prédation pourraient être aussi importants que les effets directs pour générer les fluctuations cycliques. Cette thèse vise à identifier les effets directs et indirects de la prédation qui affectent la population de lemmings bruns de l’Île Bylot, Nunavut, caractérisée par des cycles d’abondance de 3-4 ans. Pour ce faire, nous avons d’abord comparé la plausibilité de l’hypothèse de la limitation par nourriture vis-à-vis l’hypothèse de la prédation en déterminant la chronologie saisonnière des cycles des lemmings. Ensuite, nous avons construit en 2012-2013 une clôture de 9 ha coiffée d’un filet anti-prédateur aviaire dans lequel nous avons piégé les lemmings de 2013 à 2015. Une deuxième grille de trappage sans clôture a été utilisée à des fins de comparaisons. Ces deux grilles étaient actives dès 2008, ce qui nous a permis d’avoir un contrôle pré-expérimental pour les données démographiques (effets directs). En 2014 et 2015, nous avons récolté les fèces des lemmings dans les deux grilles de trappage afin de quantifier les métabolites d’hormones de stress. Une validation de la mesure des métabolites fécales des glucocorticoïdes (i.e. hormones de stress) a été menée afin de mesurer le stress des lemmings de façon non-invasive. Les résultats sont clairs : (1) le déclin des lemmings se produit à la fin de l’été alors que les prédateurs sont au plus fort de leur abondance et pas à la fin de l’hiver, supportant ainsi l’hypothèse de la limitation par la prédation. Nos résultats suggèrent aussi (2) que les lemmings à l’intérieur de la clôture avaient une survie plus élevée qu’à l’extérieur, favorisant ainsi une croissance plus forte de la population. Ensuite, (3) les lemmings ont montré des niveaux de stress plus faibles sans prédation sans toutefois que cela ait un impact sur leur reproduction. À la lumière des résultats de cette thèse et en les comparant avec deux autres études ayant aussi réduit expérimentalement l’abondance des prédateurs dans la toundra arctique, nous pouvons conclure que la prédation est la force trophique dominante de régulation de l’abondance des lemmings. Cette étude montre également que le stress induit par la prédation est insuffisant pour avoir un impact sur la dynamique des lemmings en été, soit pendant la saison où la prédation est maximale. Il est possible que cette absence d’effet soit une réponse adaptative des lemmings pour maintenir une reproduction élevée face à une prédation élevée, et ainsi maximiser leur aptitude phénotypique.Populations characterised by cyclic fluctuations have fascinated and continue to generate a great interest among the scientific community because of the complexity of the regulating factors. Several hypotheses have been proposed to explain these cyclical fluctuations but no consensus has yet been reached despite nearly 100 years of research. The availability of food and social effects (e.g. competitive interactions) has been proposed as factors responsible for cycles in certain species. However, predation is probably the factor most likely to cause cyclical fluctuations in wildlife populations due to its delayed density-dependence. A circular tandem of rarefaction and densification of predators and prey caused by direct effects (i.e. mortalities) can cause cycles of abundance. Moreover, recent studies show that indirect effects of predation such as stress could be as important as direct effects in generating cycles. This thesis aims to identify direct and indirect effects of predation that affect the cyclic brown lemming populations of Bylot Island, Nunavut, which is characterized by 3-4 yr cycles. To do this, we first compared the plausibility of the food limitation hypothesis vs. the predation limitation hypothesis by determining the seasonal timing of lemming cycles. We then we built a 9-ha fence in 2012-2013 covered by an anti-avian predator net in which we trapped lemmings from 2013 to 2015. A second control trapping grid was used for comparisons. These two grids were active since 2008, allowing us to have a pre-experimental control for demographic parameters (direct effects). In 2014 and 2015, we collected lemming feces in the two trapping grids to quantify stress hormone metabolites. A validation of the measurement of fecal glucocorticoid metabolites (i.e. stress hormones) was conducted to measure stress non-invasively. The results are clear: (1) the decline of lemmings occurs in late summer when predators are at their peak abundance and not in late winter, thereby supporting the predator-limitation hypothesis. Our results also suggest (2) that lemmings within the fence had higher survival than outside, thus promoting a higher growth of the population. Then, (3) even though lemmings had lower stress levels without predation, stress had no impact on their reproduction. In light of the results of this thesis and according to two other studies during which predator abundance was also reduced experimentally in the Arctic tundra, I conclude that predation is the dominant trophic force that regulates the abundance of lemmings. This study also shows that the stress induced by predation is insufficient to affect the dynamics of lemmings in summer, when predation is maximum. It is possible that this lack of an effect is an adaptive response by lemmings to maintain high reproductive rate despite high predation, and thus maximize their fitness

Climate variability and density-dependent population dynamics: Lessons from a simple High Arctic ecosystem

Ecologists are still puzzled by the diverse population dynamics of herbivorous small mammals that range from high-amplitude, multiannual cycles to stable dynamics. Theory predicts that this diversity results from combinations of climatic seasonality, weather stochasticity, and density-dependent food web interactions. The almost ubiquitous 3- to 5-y cycles in boreal and arctic climates may theoretically result from bottom-up (plant–herbivore) and top-down (predator–prey) interactions. Assessing, empirically, the roles of such interactions and how they are influenced by environmental stochasticity has been hampered by food web complexity. Here, we take advantage of a uniquely simple High Arctic food web, which allowed us to analyze the dynamics of a graminivorous vole population not subjected to top-down regulation. This population exhibited high-amplitude, noncyclic fluctuations—partly driven by weather stochasticity. However, the predominant driver of the dynamics was overcompensatory density dependence in winter that caused the population to frequently crash. Model simulations showed that the seasonal pattern of density dependence would yield regular 2-y cycles in the absence of stochasticity. While such short cycles have not yet been observed in mammals, they are theoretically plausible if graminivorous vole populations are deterministically bottom-up regulated. When incorporating weather stochasticity in the model simulations, cyclicity became disrupted and the amplitude was increased—akin to the observed dynamics. Our findings contrast with the 3- to 5-y population cycles that are typical of graminivorous small mammals in more complex food webs, suggesting that top-down regulation is normally an important component of such dynamics

Density‐dependent demography and movements in a cyclic brown lemming population

Abstract Theoretical modeling predicts that both direct and delayed density‐dependence are key factors to generate population cycles. Deciphering density‐dependent processes that lead to variable population growth characterizing different phases of the cycles remains challenging. This is particularly the case for the period of prolonged low densities, which is inherently data deficient. However, demographic analyses based on long‐term capture–mark–recapture datasets can help resolve this question. We relied on a 16‐year (2004–2019) live‐trapping program to analyze the summer demography and movements of a cyclic brown lemming population in the Canadian Arctic. More specifically, we examined if inversely density‐dependent processes could explain why population growth can remain low during the prolonged low phase. We found that the proportion of females in the population was inversely density‐dependent with a strong male‐biased sex ratio at low densities but not at high densities. However, survival of adult females was higher than adult males, but both had lower survival at low densities than at high ones. Distances moved by both adult males and females were density‐dependent, and proportion of females in reproductive condition was weakly density‐dependent as it tended to increase at low density. Individual body condition, measured as monthly change in body mass, was not density‐dependent. Overall, the strong male‐biased sex ratio at very low densities suggests a loss of reproductive potential due to the rarity of females and appears to be the most susceptible demographic factor that could contribute to the prolonged low phase in cyclic brown lemmings. What leads to this sex‐bias in the first place is still unclear, potentially owing to our trapping period limited to the summer, but we suggest that it could be due to high predation rate on breeding females in winter

Life in the fast lane: learning from the rare multi-year recaptures of brown lemmings in the High Arctic

Inter-annual recaptures of Arctic lemmings are extremely rare because their life expectancy is very short, typically less than one year. On Bylot Island, Nunavut, Canada, we live-trapped in summer, marked and released brown lemmings (Lemmus trimucronatus Kerr 1792) between 2004 and 2016 and we performed a large-scale, Before-After Control-Impact experiment from 2014 to 2016 to study effects of predator reduction on their population dynamics. Although inter-annual recaptures of marked lemmings were rare, our long-term study and predator reduction allowed us to capture 21 (1.4%; n = 1523) individuals over two consecutive years and one over three consecutive years. The inter-annual recapture rate was much higher in the predator-reduction grid (5.7%, n = 193) than in the other grids (0.7%, n = 425) during the experiment. Average distance moved between inter-annual recaptures was small (74 m). Our data thus demonstrate that lemmings are physiologically capable of living up to 24 months in the High Arctic, that predation is a major factor affecting lemming survival, including over winter, and that they show high site fidelity among years.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

An illustrated key to the mandibles of small mammals of eastern Canada

Skulls are often used to identify small mammals, and most identification keys to small mammals have been developed on the assumption that whole skulls will be available. However, the skulls of small mammals are seldom found intact in predator pellets or nests, and the bones of several individuals are often scattered and mixed, making counting impossible without the use of a specific cranial part. In addition, only a few keys include all the species found in the eastern provinces of Canada.Mandibles readily resist degradation by the gastric acids of both avian and mammalian predators and are often found intact in food caches of mustelids and in bat hibernacula. We therefore designed an illustrated dichotomous key to small mammals (mean mass <5 kg) of eastern Canada based on diagnostic mandible characters (including the teeth and one dentary bone). We identified and confirmed diagnostic characters to distinguish 55 species from the orders Lagomorpha, Rodentia, Soricomorpha, Carnivora, and Chiroptera. These diagnostic characters are based on a review of the literature and were confirmed by measurements performed on both museum and trapped specimens. In order to facilitate identification, photographic illustrations are provided for each couplet of the key.The ability to identify small mammals using their mandibles will reduce the number of skull components needed and has proven to be a useful tool in the study of the diet of predators. This key may also be helpful in identifying bats in the genera Myotis, Perimyotis, and Eptesicus, which are presently affected by the spread of white-nose syndrome (caused by Pseudogymnoascus destructans) throughout the eastern part of Canada

An illustrated key to the mandibles of small mammals of eastern Canada

Skulls are often used to identify small mammals, and most identification keys to small mammals have been developed on the assumption that whole skulls will be available. However, the skulls of small mammals are seldom found intact in predator pellets or nests, and the bones of several individuals are often scattered and mixed, making counting impossible without the use of a specific cranial part. In addition, only a few keys include all the species found in the eastern provinces of Canada.Mandibles readily resist degradation by the gastric acids of both avian and mammalian predators and are often found intact in food caches of mustelids and in bat hibernacula. We therefore designed an illustrated dichotomous key to small mammals (mean mass <5 kg) of eastern Canada based on diagnostic mandible characters (including the teeth and one dentary bone). We identified and confirmed diagnostic characters to distinguish 55 species from the orders Lagomorpha, Rodentia, Soricomorpha, Carnivora, and Chiroptera. These diagnostic characters are based on a review of the literature and were confirmed by measurements performed on both museum and trapped specimens. In order to facilitate identification, photographic illustrations are provided for each couplet of the key.The ability to identify small mammals using their mandibles will reduce the number of skull components needed and has proven to be a useful tool in the study of the diet of predators. This key may also be helpful in identifying bats in the genera Myotis, Perimyotis, and Eptesicus, which are presently affected by the spread of white-nose syndrome (caused by Pseudogymnoascus destructans) throughout the eastern part of Canada

Lemming winter habitat: the quest for warm and soft snow

International audienceDuring the cold arctic winter, small mammals like lemmings seek refuge inside the snowpack to keep warm and they dig tunnels in the basal snow layer, usually formed of a soft depth hoar, to find vegetation on which they feed. The snowpack, however, is a heterogenous medium and lemmings should use habitats where snow properties favor their survival and winter reproduction. We determined the impact of snow physical properties on lemming habitat use and reproduction in winter by sampling their winter nests for 13 years and snow properties for 6 years across 4 different habitats (mesic, riparian, shrubland, and wetland) on Bylot Island in the Canadian High Arctic. We found that lemmings use riparian habitat most intensively because snow accumulates more rapidly, the snowpack is the deepest and temperature of the basal snow layer is the highest in this habitat. However, in the deepest snowpacks, the basal depth hoar layer was denser and less developed than in habitats with shallower snowpacks, and those conditions were negatively related to lemming reproduction in winter. Shrubland appeared a habitat of moderate quality for lemmings as it favored a soft basal snow layer and a deep snowpack compared with mesic and wetland, but snow conditions in this habitat critically depend on weather conditions at the beginning of the winter. With climate change, a hardening of the basal layer of the snowpack and a delay in snow accumulation are expected, which could negatively affect the winter habitat of lemmings and be detrimental to their populations

Snow hardness impacts intranivean locomotion of arctic small mammals

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Snow physical properties may be a significant determinant of lemming population dynamics in the high Arctic

International audienceCyclic population fluctuations are common in boreal and Arctic species but the causes of these cycles are still debated today. Among these species, lemmings are Arctic rodents that live and reproduce under the snow and whose large cyclical population fluctuations in the high Arctic impact the whole tundra food web. We explore, using lemming population data and snow modeling, whether the hardness of the basal layer of the snow-pack, determined by rain-on-snow events (ROS) and wind storms in autumn, can affect brown lemming population dynamics in the Canadian high Arctic. Using a 7-year dataset collected on Bylot Island, Nunavut, Canada over the period 2003-2014, we demonstrate that liquid water input to snow is strongly inversely related with winter population growth (R 2 ≥ 0.62) and to a lesser extent to lemming summer densities and winter nest densities (R 2 = 0.29-0.39). ROS in autumn can therefore influence the amplitude of brown lemming population fluctuations. Increase in ROS events with climate warming should strongly impact the populations of lemmings and consequently those of the many predators that depend upon them. Snow conditions may be a key factor influencing the cyclic dynamics of Arctic animal populations. Résumé : Des fluctuations cycliques de population sont fréquentes chez des espèces boréales et arctiques mais les causes de ces cycles sont encore débattues. Parmi ces espèces, les lemmings sont des rongeurs arctiques qui vivent et se reproduisent sous la neige et dont les grandes variations de population cycliques dans le haut-arctique impac-tent tout le réseau trophique toundrique. Au moyen de données sur les populations de lemming et de modélisation de la neige, nous examinons la possibilité que la dureté de la couche de neige basale, déterminée par des évènements de pluie sur neige (PSN) e