Is there an optimal number of helpers in alpine marmot family groups?

The consequence of helping behavior on breeders fitness is still controversial. We used multivariate analyses to investigate for the effects of male and female subordinates on breeders ’ components of fitness in the Alpine marmot, Marmota marmota. We found that male and female subordinates, respectively, increased and decreased juvenile survival during winter. Thus, we give evidence that male subordinates should be considered as helpers, and that helpers provided breeders with immediate reproductive success gains, whereas subordinates females were costly. Helpers had no positive effects on female body condition, on persistence (future survival) of dominants, and on future reproduction (occurrence and size of a litter). Helpers thus did not provide breeders with delayed fitness benefits, and therfore, the load-lightening hypothesis was not supported. On the contrary, helpers had delayed fitness cost for dominant males and, consequently, for dominant females. Immediate benefits counterbalanced by delayed costs suggested an optimal number of helpers in the family group both from male and female perspectives. An optimality model well predicted the observed mean number of helpers in Alpine marmot family groups. Optimal numbers of helpers were slightly different for males and females, suggesting a potential conflict of interest between dominants. We finally discuss the possible mechanisms of helping that may explain the observed pattern in the Alpine marmot. Key words: cooperative breeding, load-lightening hypothesis, Marmota marmota, mixed models, optimality. [Behav Ecol 15:916–924 (2004)] The evolution of cooperative breeding has stimulatedtheoretical and empirical work and remains an open field of research (Cockburn, 1998). The fitness consequences of cooperative breeding have been considered both for helper

Améliorer la prise en compte des fonctionnalités écologiques dans la séquence Éviter-Réduire-Compenser

National audienceThe mitigation hierarchy does not give enough importance to the impacts of development projects on habitat connectivity. However, environmental policies and the objective of no net loss of biodiversity underline the importance of preserving ecological networks to limit the habitat fragmentation. The failure to take full account of spatial dynamics and understanding of ecological functionalities cause these gaps at all stages of project design. We propose here a methodological framework encompassing all these steps: from the assessment of conservation issues, by quantifying the overall impact of a development project on the habitat connectivity, to the dimensioning of ecological measures, by defining their optimal location to maximize their gains. We combine a species distribution model with a landscape functional connectivity model. The case study of the new football stadium in the metropolis of Lyon has highlighted the importance of this integrated approach to decision-making processes in land-use planning. This method is a valuable contribution to support both policy makers and project developers applying the mitigation hierarchy to protect biodiversity, as well as for environmental authorities.L'application de la séquence Eviter-Réduire-Compenser (ERC) n'accorde pas assez d'importance aux effets des projets d'aménagement sur les connectivités écologiques. Pourtant les politiques environnementales et l'objectif de non-perte nette de biodiversité qui en découle soulignent l'intérêt de la préservation des réseaux écologiques pour limiter la fragmentation du paysage. Le manque d'appréhension des dynamiques spatiales et de compréhension des fonctionnalités écologiques est en effet souvent mis en cause pour expliquer ces lacunes à toutes les étapes de la conception d'un projet. Nous proposons ici un cadre méthodologique englobant toutes ces étapes : de l'évaluation des enjeux de conservation, en quantifiant l'impact global d'un projet d'aménagement sur la connectivité des habitats, au dimensionnement des mesures ERC, en définissant leur emplacement optimal pour maximiser le gain qu'elles procurent. Nous couplons pour cela un modèle de distribution des espèces avec un modèle basé sur la théorie des graphes intégrant des indices de connectivités des habitats. L'application de la démarche au projet du Grand Stade dans la métropole de Lyon a mis en évidence l'intérêt de cette approche intégrée aux processus décisionnels en matière d'aménagement du territoire. Les informations offertes par cette méthode constituent ainsi une contribution précieuse à l'appui tant pour les décideurs et des concepteurs de projets qui appliquent la séquence ERC pour protéger la biodiversité, que pour les autorités environnementales