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Plard F.,University of Lyon | Plard F.,French National Center for Scientific Research | Yoccoz N.G.,University of Tromso | Bonenfant C.,University of Lyon | And 5 more authors.
Journal of Animal Ecology | Year: 2015

Early survival is a key life-history trait that often accounts for a large part of the variation in individual fitness and shapes population dynamics. The factors influencing early survival are multiple in large herbivores, including malnutrition, predation, cohort variation or maternal effects. However, the mechanistic pathways connecting these drivers to variation in early survival are much less studied. Indeed, whether these factors influence early survival directly or indirectly through early growth remains to be disentangled. In this study, we used a path analysis to separate the direct and indirect (i.e. mediated by early growth) pathways through which sex, birth date, cohort and family effects influence early survival. We used a large data set of marked roe deer newborns collected from 1985 to 2010 in the intensively monitored population of Trois Fontaines (France). We found that most drivers have indirect influences on early survival through early growth. Indeed, cohort effects influenced early survival through the indirect effect of precipitation around birth on early growth. Precipitation also had direct effects on early survival. Family effects indirectly influenced early survival. Twins from the same litter grew at about the same rate, so they had the same fate. Moreover, some factors, such as birth date, had both direct and indirect effects on roe deer early survival, with fawns born early in the season benefiting from high early survival both because they have more time to grow before the harsh season and because they grow faster during their first days of life than late-born fawns. These findings suggest that most drivers of early survival previously identified in large mammalian herbivores may affect early survival primarily through their influence on early growth. Disentangling the direct and indirect pathways by which different factors influence early survival is of crucial importance to understand the mechanisms shaping this key component of individual fitness. © 2015 British Ecological Society. Source

Plard F.,University of Lyon | Gaillard J.-M.,University of Lyon | Coulson T.,University of Oxford | Hewison A.J.M.,French National Institute for Agricultural Research | And 5 more authors.
Ecology | Year: 2015

The timing of birth has marked impacts on early life and early development of newborns in many species. In seasonal environments, early-born offspring often survive and grow better than late-born offspring, but despite the long-lasting effects of early conditions on life history traits, the influence of birth date on fitness has rarely been investigated for longlived species. In this study, we analyzed both the short- and long-term effects of birth date on individual life history traits and explored its subsequent impact on individual fitness in a population of roe deer. We considered both the direct effects, as well as the indirect effects of birth date mediated through the effects of body mass, on demographic parameters. We found that in addition to short-term effects on early body growth and survival, birth date generates ''silver spoon'' effects on adult life history traits of female roe deer. Birth date had long-lasting effects on female adult body mass such that early-born females were, on average, 3 kg heavier as adults than late-born females, although female adult survival was similar between these categories. Based on the observed relationships between birth date, body mass, and demographic parameters, we built an integral projection model describing the simultaneous distributions of birth date and body mass to quantify the fitness consequences of birth date. We found that the fitness of early-born females was higher than that of late-born females. These long-lasting effects of birth date on fitness were mostly mediated through the influence of birth date on recruitment and adult body mass. By determining development of newborns during the early stages of life, birth date has a critical influence on each step of an individual's subsequent life history trajectory. © 2015 by the Ecological Society of America. Source

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