진학프로석·박사 채용 접수 플랫폼

The Alpine Ecology Laboratory is a joint research unit with 3 supervisory bodies, CNRS, USMB and UGA, whose research aims to understand the mechanisms behind biodiversity and its dynamics, to decipher its role in the functioning of socio-ecosystems, and to predict its response to anthropogenic pressures, with a focus on Alpine environments. The USMB research group is mainly interested in the interaction networks between herbivores (large herbivores and insects), plant communities, predators and human activities, and the consequences of these interactions on the functioning of socio-ecosystems.

In population ecology, cohort effects describe variations in life history traits depending on birth conditions, variations that can persist throughout the life of individuals (Albon et al. 1987). A distinction is made between short-term numerical effects causing variable recruitment depending on juvenile survival, and long-term quality effects on the phenotypic and reproductive performance of individuals surviving to adulthood (Gaillard et al. 2003). For example, the summer survival rate of fawns varies from 20 to 90% depending on the year (Gaillard et al. 2013). Similarly, females born in difficult environmental conditions (e.g., high density) have lower reproductive success than those born in conditions more favorable to their development. These cohort effects have been demonstrated in many vertebrate species and in a growing number of biological traits (body mass, dispersion, personality, etc.). The demographic consequences of these cohort effects have been studied on several occasions, either empirically or theoretically (Lindstrom & Kokko 2002, Tuljapurkar 1989). Simulations suggest that cohort effects, by generating variations in demographic parameters in adulthood, destabilize the dynamics of relatively stable populations but can stabilize those of unstable populations (Lindstrom & Kokko 2002). At first glance, the temporal variability in recruitment generated by short-term cohort effects should lead to a decrease in the long-term growth rate of populations. The consequences of cohort effects on adult performance are more difficult to understand. Adult demographic parameters will depend on the number of individuals in each cohort that survive to adulthood. Poor cohorts should contribute little to population dynamics because only a small number of individuals will survive the first year of life under these conditions. However, very strong selection for viability in these cohorts subject to high mortality rates could compensate for the low number of individuals by leaving only those of very good quality with strong phenotypic and demographic performance (Garratt et al. 2015), thereby limiting the temporal variation in adult demographic parameters. In his monograph on stochastic demography, Tuljapurkar (1989) proposed a theoretical way to quantify the contribution of cohort effects to the temporal variation in the long-term growth rate of populations, which, to our knowledge, has never been tested with empirical data sets. The objective of this postdoctoral research is therefore to apply the method proposed by Tuljapurkar (1989) to populations of large herbivorous mammals (deer, elk, chamois) and to identify the biological factors that may explain the variability in the contribution of cohort effects to population dynamics.

Albon, S. D., Clutton-Brock, T. H., & Guinness, F. E. (1987). Early development and population dynamics in red deer. II. Density-independent effects and cohort variation. The Journal of Animal Ecology, 69-81.

Gaillard, J. M., Loison, A., ToÏgo, C., Delorme, D., & Van Laere, G. (2003). Cohort effects and deer population dynamics. Ecoscience, 10(4), 412-420.

Gaillard, J. M., Mark Hewison, A. J., Klein, F., Plard, F., Douhard, M., Davison, R., & Bonenfant, C. (2013). How does climate change influence demographic processes of widespread species? Lessons from the comparative analysis of contrasted populations of roe deer. Ecology letters, 16, 48-57.

Garratt, M., Lemaître, J. F., Douhard, M., Bonenfant, C., Capron, G., Warnant, C., ... & Gaillard, J. M. (2015). High juvenile mortality is associated with sex-specific adult survival and lifespan in wild roe deer. Current Biology, 25(6), 759-763.

Lindström, J., & Kokko, H. (2002). Cohort effects and population dynamics. Ecology Letters, 5(3), 338-344.

Tuljapurkar, S. (1989). Population dynamics in variable environments (Vol. 85). Springer Science & Business Media.