Heterogeneity in individual life-history trajectories over age: quantifying the relative importance of ontogeny, selection, and environment.
The quantification of how life history traits vary with age is fundamental because age-specific variations affect evolution of traits and their influence on population dynamics. Changes in life history traits with age occur at the individual level, but most previous studies of age-specific changes at the population level did not account for individual heterogeneity, a fundamental element shaping population responses and evolutionary processes. Although some recent studies have demonstrated the importance of individual heterogeneity to understand the ontogenetic processes observed in populations, very few studies have tried to quantify the relative contributions of these evolutionary processes. In this project, our goal is to partition and quantify the roles of ontogenetic, selection, and environmental processes on changes in life-history traits with age, and to compare the contributions of these processes among species and traits. Achieving this goal, however, requires improved biostatistical methods to model heterogeneity among individuals in a population. A key aspect of this project is therefore to perform a statistical evaluation of the methods commonly used in longitudinal studies, and develop more effective alternative methods.
This project builds on a major international collaboration that provides access to longitudinal data on individually marked animals monitored from birth to death in 14 populations (10 ungulate species) studied intensively for 10-40 years. Our aim is to assess the relative contribution of each process and compare them among species that show contrasted dynamics and vary in their position along the slow-fast continuum, as well as among populations of the same species living under contrasting environmental conditions. Overall, the project should provide two major scientific contributions: robust analytical methods of life history strategies and a better understanding of evolution of life history strategies.