Beyond predator satiation : masting but also the effects of rainfall stochasticity on weevils drive acorn predation

Escaping seed predation is a classic "economy of scale" hypotheses (predator satiation hypothesis, Psh) to explain the selection for the synchronous production of massive and nil seed crops (masting) in plants. The Psh postulates that predator satiation occurs through a combination of (1) "functional satiation," as not all seeds can be consumed during a massive crop, and (2) "numerical satiation," as predator populations collapse during poor crop years. Many studies advocate for the Psh, but few have investigated the importance of masting compared to other factors for the control of predation extent. Namely, environmental cues prompting masting could also determine predator's success and, ultimately, influence directly and independently seed predation intensity. We explored this question in Mediterranean oaks, as they exhibit strong masting behavior; acorns are heavily predated upon by weevils; and rainfall stochasticity drives masting and the emergence of adult weevils from the soil. Results of two mid-term studies (4 and 11 yr) showed that acorn production and predation were highly variable across years, while the abundance of adult weevils was positively related to autumn rainfall and to the number of infested acorns the previous years. Ultimately, acorn predation was negatively influenced by inter-annual fluctuation of seed production (masting) yet, mainly and positively, prompted by autumn rainfall and acorn crop size (only in one site). Our results highlight the relevance of masting to reduce seed predation. Yet evidences that rainfall stochasticity directly determines the success of weevils, and it independently influences seed predation extent, indicate that environmental cues prompting masting may also fine-tune the output of this reproductive behavior. Additionally, local differences suggest that the relevance of masting may change with tree characteristics (low vs. high seed production) and landscape structure (isolated vs. dense forests). We also discuss what can be the effects of increasing drought in Mediterranean areas for this antagonistic interaction, triggered by rainfall

SIZE DIFFERENCE IN WHOOPING CRANES REARED FOR TWO REINTRODUCTION METHODS

We investigated a possible size difference in whooping cranes (Grus americana) captive-reared for 2 reintroduction methods to establish a migratory population in eastern North America. Cranes reared for ultralight aircraft-led migration (UL) to Florida were significantly larger than cranes reared for direct autumn release (DAR) on the natal area in central Wisconsin. Mean tarsal length was 315.5 ± 0.98 (1 SE) and 308.1 ± 1.87 mm, respectively, for UL and DAR males and 296.9 ± 1.03 and 290.8 ± 2.60 mm, respectively, for UL and DAR females. Because of the different rearing schedules, eggs for the DAR method were generally laid later than eggs for UL. Eggs later in the laying sequence had lower weights and resulted in smaller birds, although this overall effect was small. Size difference did not appear related to genetic factors. Although survival to 5 years after release was not significantly related to size within groups of the same sex and release method, captive-rearing effects such as size on survival and behavior of released birds should be considered in assessment of reintroduction programs

The influence of landscape structure on female roe deer home-range size

10 pagesInternational audienceAnimal distribution and abundance are greatly affected by the availability of their food resources, which also depends on landscape structure. Lothar hurricane in 1999 had profoundly modified the structure of the forests in France, affecting the habitat quality of ungulates. We tested whether the variations in home-range size of 23 female roe deer were influenced by the fragmentation of the landscape caused by Lothar in the Chize´ forest, namely by the increase in heterogeneity associated with the localized massive tree felling. Home-range size was studied in the summers of 2001 and 2002 and we found that variation in home-range size was mainly explained by only one landscape variable: edge density. Home-range size decreased as edge density increased, which is consistent with the fact that edges are good browsing habitats for roe deer. The result of this study suggests that, after 2 years, the hurricane had improved the quality of the home ranges by creating more forest heterogeneity and increasing the contacts between the different vegetation patches within the home range. These results highlight the fact that spatial heterogeneity is likely to be a key factor influencing the distribution and local population density

Estimation des effectifs de saumons reproducteurs : une approche unificatrice

National audienc

Estimating population size of migrating adults of salmonids : a unifying approach

International audienc

Tagging piglets at the farrowing nest in the wild: Some preliminary guidelines

Neonate ungulate often show high rates of mortality due to predation, starvation, orexposure to bad weather, leading to losses frequently exceeding 50%. Wild boar piglets are known tosuffer from thermoregulation insufficiency, which probably explain the nest construction behaviour insows. We thus tried to develop a method for tagging piglets inside their farrowing (or birth) nest toassess piglet survival from few days after their birth onwards. Sows fitted-out with VHF collars wereradio-tracked to determine parturition time, and to get a rough idea of the possible birth nest location.Then, with a handled antenna we approached on foot the birth nest, and piglets were caught, taggedand fitted-out with a backpack transmitter and released inside the nest. Temporal movements ofmother and litter association were monitored, as long as possible. Results on sow behaviour and tacticagainst human approach, piglets body mass, piglet reaction, and survival in their early lifetime weredescribed

Dynamique d'une population chassée de sangliers (Sus scrofa scrofa) en milieu forestier

Au sein des Ongulés sauvages, le Sanglier (Sus scrofa scrofa) se distingue par une combinaison bien particulière de traits d histoire de vie associant une fécondité élevée et un âge de première reproduction précoce à, une grande taille et une forte espérance de vie potentielle. De plus, au contraire de la plupart des autres ongulés qui sont des herbivores assez stricts, le Sanglier est omnivore. Cette stratégie d histoire de vie peu commune est associée à un fort succès en terme d effectifs, puisqu en Europe, les populations de Sanglier sont en pleine expansion et sont à l origine de problèmes socio-e conomiques principalement en raison des dégâts occasionnés aux activités humaines. Il est donc indispensable de déterminer les facteurs explicatifs de cette augmentation des effectifs et de développer un modèle de fonctionnement de populations pour réussir à mieux gérer la situation. Ce travail s appuie sur une étude à long terme (25 ans) d une population chassée de l Est de la France (Haute-Marne). L analyse de l allocation maternelle dans la reproduction met en évidence que la sexe ratio in utero varie en fonction de la taille de la portée avec : une sexe ratio biaisée envers les mâles pour les portées de taille inférieure ou égale à six et une sexe ratio biaisée envers les femelles pour les portées de plus de six fœtus. Ce patron de variation peu commun pourrait avoir évolué sous la pression de sélection contre les grandes tailles de portée au sein desquelles une trop forte compétition apparaît entre frères et sœurs et ce, afin de maximiser le nombre de jeunes recrutés. Le poids seuil pour que les femelles puissent se reproduire est d environ 28 kg (poids vif) et une fois la maturité sexuelle acquise, ces femelles sont susceptibles de se reproduire chaque année. Les ressources disponibles influencent cependant la phénologie de la reproduction qui varie d une année à l autre. La mortalité naturelle a pu être différenciée de celle due à la chasse grâce à l emploi des modèles récemment développés de Capture-Recapture Multi-Etats. Les mâles ont une survie constante au cours du temps mais différente selon leur âge et une probabilité d être tués à la chasse qui augmente avec l âge jusqu à atteindre près de 70%. La survie des femelles varient plus fortement entre années et diffère aussi selon l âge avec, des femelles de moins de un an qui ont un taux de survie annuel inférieur aux femelles les plus âgées. Relativement aux autres grands mammifères, la survie des femelles adultes est plus faible et plus variable au cours du temps, peut-être en réponse à un investissement plus fort dans la reproduction, en particulier pour les jeunes adultes. Ces spécificités démographiques démontrent que le Sanglier ne peut donc être soumis aux mêmes règles de gestion que les autres Ongulés. Nous avons développé un modèle de gestion de population structuré en classe de sexe et de poids afin que les gestionnaires puissent comparer les résultats du modèle avec la distribution observée dans le tableau de chasse et apprécier ainsi l efficacité des modalités de gestion qu ils appliquentAmong Ungulates, the wild boar (Sus scrofa scrofa) is characterised by a mixture of particular life history traits which associate a high fecundity and an early age at first reproduction with a large body size and a potential long life expectancy. Moreover, unlike most ungulates which are rather strict herbivores, the wild boar is an omnivore. This uncommon life-history strategy is associated with an increase in population size. Indeed, in Europe, wild boar populations are currently still growing and cause some socio-economical problems due to the damage that wild boars generate to the human activities. Hence the understanding of the factors primarily involved in this increase in population size as well as the modelling of population dynamics is now essential to better manage wild boar populations. This work rely on a long term data set (25 years) of a hunted wild boar population in the eastern part of France (Haute-Marne). The analyses of maternal allocation in reproduction highlighted that in utero, the sex ratio decreased as litter size increased. Sex ratio was male-biased for litter size up to 6 and then became female-biased in larger litters. Producing large female-biased litters may be an adaptive adjustment to avoid strong sibling competition during lactation and therefore to maximise the number of recruited offspring. The threshold weight above which females can reproduce is around 28 kg live weight but once females become sexually mature, they will reproduce every year. However, the onset of oestrus may be delayed according to the available resources and vary year-to-year. Natural mortality was disentangled from hunting mortality by using Capture-Recapture multi-states models. Males survival did not vary yearly but did vary with age-classes and the probability to be hunted increased with age up to around 70%. Females survival did vary yearly and also differed between age-classes with the yearly survival probability of females younger than one-year old being smaller than that of older females. Compared to other large mammals, adult females survival was lower and more variable over time possibly because of higher reproductive investment, especially in young adults. Those demographic characteristics reveal that wild boars could not be managed like other ungulate species. So, we developed a new modelling approach and retained a sex-specific body mass-dependent model to assist managers. In this way, managers have the possibility to directly test the outcome of the model by comparing observed and expected distributions of wild boars killed by hunters among sex- and body mass-specific classes. They can assess the performance of a given hunting rule and simulate the respective efficiency of management scenariosLYON1-BU.Sciences (692662101) / SudocSudocFranceF