Effekterna av en invasiv växt på afrikanska stora växtätare

Invasive plants, growing and spreading outside of their native range, can severely modify ecosystems. Herbivory has often been seen as a potential control of invasions, but has rarely been considered as a potential impacted trophic level. Considering the habitat selection by large herbivore being a reflection of their feeding habits and predator avoidance, I studied the impact of the invasive Chromolaena odorata on African large herbivores in Hluhluwe-iMfolozi Park, KwaZulu-Natal, South Africa. This plant is not eaten by the animals but affects the diversity of the grass species, the height and cover of woody species and can create high and thick walls as a barrier for most animals. Abundance of 14 species of herbivores was estimated by dung counting, and the presence and density of the invasive shrub was estimated every 5 meters on 24 transects in the park in 2004 (high density of invasive) and 2014 (low density of invasive). This data was used to understand a predictive habitat selection analysis (Resource Selection Functions) and to analyse the recolonization of previously invaded patches based on the change of dung abundance. A Principal Component Analysis showed that closed woody habitats are the most invaded. The results are a mirror of the high heterogeneity of habitats and herbivores in African savannas. Grazers (buffalo, zebra, warthog, and wildebeest) as well as browsers (nyala) avoided high density patches that are a physical barrier to selection. Grazers seem also to avoid less dense patches where food availability might be diminished and where ambush predators could hide. However, bushpigs select invaded patches, which may be used as a shelter against predators for example. Other species appear to ignore the invasion; because their home area does not overlap the invaded area (impala) or because the invasion does not affect them (elephant)

Patrons et optimisation des comportements de thermo-hydrorégulation dans un paysage hétérogène

Actual climate changes drive modifications of the thermal and water landscapes where live organisms. Thermoregulation in ectotherm species mostly rely on behavioral adjustments. These adjustments buffer the negative effects of these environmental changes on the physiology and the performances of the individuals. However, too few studies focused on the costs of changes in the water environment on thermoregulation behaviors. The main objective of this thesis is to highlight behavioral patterns involved in the joint regulation of body temperature and water balance, hereafter called thermo-hydroregulation behaviors, which would be critical to understand the responses of organisms to global changes. I focused on studying space use behaviors (activity patterns, micro-habitat selection) of a temperate squamate species, the common lizard (Zootoca vivipara) through experimental set-ups in laboratory or outdoor conditions, as well as a comparative study of natural populations in the Massif Central, France. My results highlighted that behavioral regulation of the water balance can trade-off or act in synergy with thermoregulation behaviors according to environmental conditions. The observed behavioral adjustments could consist in a water conservation strategy. A decrease in water availability in the environment as well as a dehydration induced changes in thermoregulation strategies (body temperature, thermoregulation accuracy). These studies highlighted the importance of a joint consideration of the thermal and water constraints when studying the ectotherms responses to global change, and questioned our current understanding of individual and populational responses to these changes.Les changements climatiques actuels induisent des modifications du paysage thermique et hydrique dans lequel vivent les organismes. Il est attendu que les organismes ectothermes, qui régulent leur température corporelle via le comportement, aient la capacité de tamponner tout ou partie des effets négatifs de ces modifications sur la physiologie et les performances. Toutefois peu d’études se sont penchées sur les coûts que peuvent avoir les modifications de l’environnement hydrique sur les comportements de thermorégulation. L’objectif principal de cette thèse est de décrire des mécanismes comportementaux de régulation conjointe de la température corporelle et de la balance hydrique, définis alors comme comportements de thermo-hydrorégulation. Je me suis concentré sur l’étude du comportement d’un squamate de milieu tempéré, le lézard vivipare (Zootoca vivipara) à l'aide de protocoles expérimentaux et de suivis en milieu naturel. Mes résultats permettent de mettre en évidence des compromis et des synergies entre les patrons de comportements d’hydrorégulation et de thermorégulation selon les conditions environnementales. Ces ajustements comportementaux s'expliquent par une nécessité de limiter les pertes en eaux. Une diminution de la disponibilité hydrique dans l’environnement ainsi que la déshydratation de l’animal induisent aussi des modifications dans les stratégies de thermorégulation. Ces travaux suggèrent qu’une prise en compte conjointe des contraintes thermiques et hydriques dans l’environnement semble critique à l’étude des réponses des organismes aux changements globaux, et pourrait questionner notre compréhension des réponses individuelles à ces changements

Patterns and optimisation of thermo-hydroregulation behaviors in an heterogeneous landscape

Les changements climatiques actuels induisent des modifications du paysage thermique et hydrique dans lequel vivent les organismes. Il est attendu que les organismes ectothermes, qui régulent leur température corporelle via le comportement, aient la capacité de tamponner tout ou partie des effets négatifs de ces modifications sur la physiologie et les performances. Toutefois peu d’études se sont penchées sur les coûts que peuvent avoir les modifications de l’environnement hydrique sur les comportements de thermorégulation. L’objectif principal de cette thèse est de décrire des mécanismes comportementaux de régulation conjointe de la température corporelle et de la balance hydrique, définis alors comme comportements de thermo-hydrorégulation. Je me suis concentré sur l’étude du comportement d’un squamate de milieu tempéré, le lézard vivipare (Zootoca vivipara) à l'aide de protocoles expérimentaux et de suivis en milieu naturel. Mes résultats permettent de mettre en évidence des compromis et des synergies entre les patrons de comportements d’hydrorégulation et de thermorégulation selon les conditions environnementales. Ces ajustements comportementaux s'expliquent par une nécessité de limiter les pertes en eaux. Une diminution de la disponibilité hydrique dans l’environnement ainsi que la déshydratation de l’animal induisent aussi des modifications dans les stratégies de thermorégulation. Ces travaux suggèrent qu’une prise en compte conjointe des contraintes thermiques et hydriques dans l’environnement semble critique à l’étude des réponses des organismes aux changements globaux, et pourrait questionner notre compréhension des réponses individuelles à ces changements.Actual climate changes drive modifications of the thermal and water landscapes where live organisms. Thermoregulation in ectotherm species mostly rely on behavioral adjustments. These adjustments buffer the negative effects of these environmental changes on the physiology and the performances of the individuals. However, too few studies focused on the costs of changes in the water environment on thermoregulation behaviors. The main objective of this thesis is to highlight behavioral patterns involved in the joint regulation of body temperature and water balance, hereafter called thermo-hydroregulation behaviors, which would be critical to understand the responses of organisms to global changes. I focused on studying space use behaviors (activity patterns, micro-habitat selection) of a temperate squamate species, the common lizard (Zootoca vivipara) through experimental set-ups in laboratory or outdoor conditions, as well as a comparative study of natural populations in the Massif Central, France. My results highlighted that behavioral regulation of the water balance can trade-off or act in synergy with thermoregulation behaviors according to environmental conditions. The observed behavioral adjustments could consist in a water conservation strategy. A decrease in water availability in the environment as well as a dehydration induced changes in thermoregulation strategies (body temperature, thermoregulation accuracy). These studies highlighted the importance of a joint consideration of the thermal and water constraints when studying the ectotherms responses to global change, and questioned our current understanding of individual and populational responses to these changes

Seasonality impacts collective movements in a wild group-living bird

Background A challenge faced by animals living in groups with stable long-term membership is to effectively coordinate their actions and maintain cohesion. However, as seasonal conditions alter the distribution of resources across a landscape, they can change the priority of group members and require groups to adapt and respond collectively across changing contexts. Little is known about how stable group-living animals collectively modify their movement behaviour in response to environment changes, such as those induced by seasonality. Further, it remains unclear how environment-induced changes in group-level movement behaviours might scale up to affect population-level properties, such as a population’s footprint. Methods Here we studied the collective movement of each distinct social group in a population of vulturine guineafowl (Acryllium vulturinum), a largely terrestrial and non-territorial bird. We used high-resolution GPS tracking of group members over 22 months, combined with continuous time movement models, to capture how and where groups moved under varying conditions, driven by seasonality and drought. Results Groups used larger areas, travelled longer distances, and moved to new places more often during drier seasons, causing a three-fold increase in the area used at the population level when conditions turned to drought. By contrast, groups used smaller areas with more regular movements during wetter seasons. Conclusions The consistent changes in collective outcomes we observed in response to different environments raise questions about the role of collective behaviour in facilitating, or impeding, the capacity for individuals to respond to novel environmental conditions. As droughts will be occurring more often under climate change, some group living animals may have to respond to them by expressing dramatic shifts in their regular movement patterns. These shifts can have consequences on their ranging behaviours that can scale up to alter the footprints of animal populations

Intraspecific morphological variation of the middle ear in the European badger, Meles meles (Carnivora: Mustelidae)

International audienc

Temperature as a constraint on the timing and duration of African elephant foraging trips

International audienceIn arid and semi-arid environments, water is a key resource that is limited in availability. During the dry season, perennial water sources such as water pans often are far apart and shape the daily movement routines of large herbivores. In hot environments, endotherms face a lethal risk of overheating that can be buffered by evaporative cooling. Behavioral adjustments are an alternative way to reduce thermal constraints on the organism. The trade-off between foraging and reaching water pans has been studied widely in arid environments; however, few studies have looked into how ambient temperature shapes individual trips between two visits to water. In this study, we tracked during the dry season the movement of 8 GPS-collared African elephants (Loxodonta africana) cows from different herds in Hwange National Park, Zimbabwe. This species, the largest extant terrestrial animal, is particularly sensitive to heat due to its body size and the absence of sweat glands. We show that most foraging trips depart from water at nightfall, lowering the average temperature experienced during walking. This pattern is conserved across isolated elephant populations in African savannas. We also observed that higher temperatures at the beginning of the trip lead to shorter trips. We conclude that elephants adjust the timing of foraging trips to reduce the thermal constraints, arguing that further considerations of the thermal landscape of endotherms are important to understand their ecology

Water restriction induces behavioral fight but impairs thermoregulation in a dry‐skinned ectotherm

International audienceBehavioral fight responses to desiccation risk are important to predict the vulnerability of terrestrial animals to climate change and yet, they have received little attention so far. In terrestrial ectotherms, behavioral regulation of the water balance (i.e., hydroregulation) is likely to be plastic and may trade-off with thermoregulation behavior because water loss rates are generally higher in warmer environments and body temperatures.When low water availability and heat stress cause physiological dehydration, we expect to highlight a shift to behavioral water-conservation strategies including changes in activity patterns, microhabitat selection and thermoregulation strategies.Here, we compared the behavior of adult common lizards (Zootoca vivipara) in indoor arenas that either had a permanent access to water or underwent a one-week long experimental water restriction.Water-restricted lizards reduced their behavioral activity, selected more often cooler and wetter refuges during daytime, and performed less accurate thermoregulation than control lizards. The activity of water-restricted gravid females shifted towards the cooler and wetter early hours of the day. In addition, they had lower body temperatures and preferred lower body temperatures at the end of the experiment (i.e., thermal depression). Water-restricted lizards suffered from a mild physiological dehydration, water-restricted females had lower mass change compared to control ones, and water-restricted males lost weight. Heat stress was simulated every second day, which led to a range of heat avoidance and water conservation strategies independent from water restriction.5. Altogether, these results confirm that chronic water restriction and dehydration induce responses towards water conservation that conflict with thermoregulation accuracy

distancewater_density

For each random location calculated for the RSF analysis: distance to water, number of horses centroids in a 4000m buffer (centered on the random location) during the year associated with the random location

Water restriction in viviparous lizards causes transgenerational effects on behavioral anxiety and immediate effects on exploration behavior

International audienc

Short-term changes in air humidity and water availability weakly constrain thermoregulation in a dry-skinned ectotherm

International audienceThermoregulation is critical for ectotherms as it allows them to maintain their body temperature close to an optimum for ecological performance. Thermoregulation includes a range of behaviors that aim at regulating body temperature within a range centered around the thermal preference. Thermal preference is typically measured in a thermal gradient in fullyhydrated and post-absorptive animals. Short-term effects of the hydric environment on thermal preferences in such setups have been rarely quantified in dry-skinned ectotherms, despite accumulating evidence that dehydration might trade-off with behavioral thermoregulation. Using experiments performed under controlled conditions in climatic chambers, we demonstrate that thermal preferences of a ground-dwelling, actively foraging lizard (Zootoca vivipara) are weakly decreased by a daily restriction in free-standing water availability (less than 0.5˚C contrast). The influence of air humidity during the day on thermal preferences depends on time of the day and sex of the lizard, and is generally weaker than those of of free-standing water (less than 1˚C contrast). This shows that short-term dehydration can influence, albeit weakly, thermal preferences under some circumstances in this species. Environmental humidity conditions are important methodological factors to consider in the analysis of thermal preferences