Mismatch between birth date and vegetation phenology slows the demography of roe deer.

Marked impacts of climate change on biodiversity have frequently been demonstrated, including temperature-related shifts in phenology and life-history traits. One potential major impact of climate change is the modification of synchronization between the phenology of different trophic levels. High phenotypic plasticity in laying date has allowed many bird species to track the increasingly early springs resulting from recent environmental change, but although changes in the timing of reproduction have been well studied in birds, these questions have only recently been addressed in mammals. To track peak resource availability, large herbivores like roe deer, with a widespread distribution across Europe, should also modify their life-history schedule in response to changes in vegetation phenology over time. In this study, we analysed the influence of climate change on the timing of roe deer births and the consequences for population demography and individual fitness. Our study provides a rare quantification of the demographic costs associated with the failure of a species to modify its phenology in response to a changing world. Given these fitness costs, the lack of response of roe deer birth dates to match the increasingly earlier onset of spring is in stark contrast with the marked phenotypic responses to climate change reported in many other mammals. We suggest that the lack of phenotypic plasticity in birth timing in roe deer is linked to its inability to track environmental cues of variation in resource availability for the timing of parturition.

Disentangling direct and growth-mediated influences on early survival: a mechanistic approach.

1. 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. 2. 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). 3. 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. 4. 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.

Quantifying the influence of measured and unmeasured individual differences on demography.

1. Demographic rates can vary not only with measured individual characters like age, sex and mass but also with unmeasured individual variables like behaviour, genes and health. 2. Predictions from population models that include measured individual characteristics often differ from models that exclude them. Similarly, unmeasured individual differences have the potential to impact predictions from population models. However, unmeasured individual differences are rarely included in population models. 3. We construct stage- and age-structured models (where stage is mass) of a roe deer population, which are parameterized from statistical functions that either include, or ignore, unmeasured individual differences. 4. We found that mass and age structures substantially impacted model parameters describing population dynamics, as did temporal environmental variation, while unmeasured individual differences impacted parameters describing population dynamics to a much smaller extent once individual heterogeneity related to mass and age has been included in the model. We discuss how our assumptions (unmeasured individual differences only in mean trait values) could have influenced our findings and under what circumstances unmeasured individual differences could have had a larger impact on population dynamics. 5. There are two reasons explaining the relative small influence of unmeasured individual differences on population dynamics in roe deer. First, individual body mass and age both capture a large amount of individual differences in roe deer. Second, in large populations of long-lived animals, the average quality of individuals (independent of age and mass) within the population is unlikely to show substantial variation over time, unless rapid evolution is occurring. So even though a population consisting of high-quality individuals would have much higher population growth rate than a population consisting of low-quality individuals, the probability of observing a population consisting only of high-quality individuals is small.

Reduced microsatellite heterozygosity does not affect natal dispersal in three contrasting roe deer populations.

Although theoretical studies have predicted a link between individual multilocus heterozygosity and dispersal, few empirical studies have investigated the effect of individual heterozygosity on dispersal propensity or distance. We investigated this link using measures of heterozygosity at 12 putatively neutral microsatellite markers and natal dispersal behaviour in three contrasting populations of European roe deer (Capreolus capreolus), a species displaying pre-saturation condition-dependent natal dispersal. We found no effect of individual heterozygosity on either dispersal propensity or dispersal distance. Average heterozygosity was similar across the three studied populations, but dispersal propensity and distance differed markedly among them. In Aurignac, dispersal propensity and distance were positively related to individual body mass, whereas there was no detectable effect of body mass on dispersal behaviour in Chizé and Trois Fontaines. We suggest that we should expect both dispersal propensity and distance to be greater when heterozygosity is lower only in those species where dispersal behaviour is driven by density-dependent competition for resources.

High juvenile mortality is associated with sex-specific adult survival and lifespan in wild roe deer.

Male mammals typically have shorter lifespans than females [1]. Sex differences in survival may result, in part, from sex-specific optima in investment in reproduction, with higher male mortality rates from sexual competition selecting for a "live-fast die-young" strategy in this sex [2]. In the wild, lifespan is also influenced by environmental conditions experienced early in life. Poor conditions elevate juvenile mortality, which may selectively remove individuals with a particular phenotype or genotype from a cohort [3], and can alter the subsequent phenotypic condition and fate of those that survive to adulthood [4]. Males and females can respond differently to the same early-life environmental experiences [5, 6], but whether such environmental pressures generate sex differences in lifespan has rarely been considered. We show that sex differences in adult survival and lifespan in cohorts of roe deer (Capreolus capreolus) range from virtually absent in some years to females living 30% longer than males in others. The extent of this sex difference in adult longevity is strongly linked to the level of mortality each cohort experiences as juveniles, with high juvenile mortality generating a strong sex difference in both adult survival and lifespan. In females, high juvenile mortality leads to increased adult survival for those remaining individuals, whereas in males survival is actually reduced. Early environmental conditions and the selective pressures they impose may help to explain variability in sex-specific aging across animal taxa.