Influence du stress de prédation sur la reproduction de la chèvre de montagne

L’influence de la prédation sur une proie s’étend au-delà de la mortalité directe associée à la consommation d’individus. Dans certains cas, la simple présence d’un prédateur au sein d’un écosystème peut entraîner une réduction drastique de la reproduction des proies. L’induction d’un état de stress physiologique chronique pourrait être le mécanisme à l’origine de cet effet. L’objectif de mon projet était d’évaluer l’influence du stress de prédation sur la reproduction de la chèvre de montagne (Oreamnos americanus). Nous avons d’abord validé en captivité une méthode permettant d’évaluer le stress en mesurant la concentration en glucocorticoïdes dans des échantillons de fèces et de poils, puis nous avons analysé une base de données longitudinale sur une population de chèvres de montagne marquées et suivies durant toute leur vie en milieu naturel. Nos résultats indiquent que la prédation peut agir sur la reproduction de la chèvre de montagne par l’induction d’un état de stress chronique. En plus de contribuer à la compréhension des effets indirects de la prédation chez les mammifères, cette étude permet de préciser les causes du déclin d’une population sauvage de chèvres de montagne.The impact of predation on prey goes beyond the direct consumption of individuals. In some cases, the mere presence of predators in an ecosystem can drastically impair prey reproduction. The induction of chronic physiological stress could act as the mechanism underlying such effects. My objective was to assess whether predator-induced stress could impair reproduction in an alpine ungulate, the mountain goat. We first validated a method to measure physiological stress using faeces and hair as biomarkers, and then analysed a longterm data base on a population of wild marked mountain goats. Our results indicate that predation may act on reproduction in mountain goats through the induction of chronic stress. In addition to its contribution to the understanding of indirect effects of predation in mammals, this study clarifies the causes behind the decline of a wild mountain goat population

Worth the dip? Polar bear predation on swimming flightless greater snow geese and estimation of energetic efficiency

As sea-ice cover is shrinking, polar bears (Ursus maritimus, Phipps, 1774) face decreased access to seals, their primary prey, resulting in a greater dependence on terrestrial food sources. Whether polar bears can benefit from these terrestrial food sources, however, depends on their ability to find and capture prey items without expending more energy than is acquired. Here, we report one of the northernmost observations of polar bear predation on adult birds. The bear used a dive-hunting technique, which consisted of submerging itself, approaching underwater, and catching flightless greater snow geese (Anser caerulescens caerulescens (Linnaeus, 1758)) from beneath the surface of a tundra pond. After evaluating energy expenditures during swimming and energy intakes from consuming geese, we estimated that this rarely documented dive-hunting technique could be energetically profitable for a certain range of pursuit durations. This observation highlights the behavioral plasticity that polar bears can deploy to punctually exploit land-based food sources

Predator-mediated interactions through changes in predator home range size can lead to local prey exclusion: Supplementary figures, equations and methods.

The strength of indirect biotic interactions is difficult to quantify in the wild and can alter community composition. To investigate whether the presence of a prey species affects the population growth rate of another prey species, we quantified predator-mediated interaction strength using a multi-prey mechanistic model of predation and a population matrix model. Models were parameterized using behavioural, demographic and experimental data from a vertebrate community that includes the arctic fox (Vulpes lagopus), a predator feeding on lemmings and eggs of various species such as sandpipers and geese. We show that the positive effects of the goose colony on sandpiper nesting success (due to reduction of search time for sandpiper nests) were outweighed by the negative effect of an increase in fox density. The fox numerical response was driven by changes in home range size. As a result, the net interaction from the presence of geese was negative and could lead to local exclusion of sandpipers. Our study provides a rare empirically based model that integrates mechanistic multi-species functional responses and behavioural processes underlying the predator numerical response. This is an important step forward in our ability to quantify the consequences of predation on community structure and dynamics

Global COVID-19 lockdown highlights humans as both threats and custodians of the environment

The global lockdown to mitigate COVID-19 pandemic health risks has altered human interactions with nature. Here, we report immediate impacts of changes in human activities on wildlife and environmental threats during the early lockdown months of 2020, based on 877 qualitative reports and 332 quantitative assessments from 89 different studies. Hundreds of reports of unusual species observations from around the world suggest that animals quickly responded to the reductions in human presence. However, negative effects of lockdown on conservation also emerged, as confinement resulted in some park officials being unable to perform conservation, restoration and enforcement tasks, resulting in local increases in illegal activities such as hunting. Overall, there is a complex mixture of positive and negative effects of the pandemic lockdown on nature, all of which have the potential to lead to cascading responses which in turn impact wildlife and nature conservation. While the net effect of the lockdown will need to be assessed over years as data becomes available and persistent effects emerge, immediate responses were detected across the world. Thus initial qualitative and quantitative data arising from this serendipitous global quasi-experimental perturbation highlights the dual role that humans play in threatening and protecting species and ecosystems. Pathways to favorably tilt this delicate balance include reducing impacts and increasing conservation effectiveness