Résumé
The slow-fast continuum is known to structure variation in life-history
strategies across species. Within populations, it is also assumed to
structure individual life histories, yet evidence of its existence remains
unclear. We formally assessed the presence of a slow-fast continuum of
life histories both within populations and across species using detailed
individual-based data for 17 bird and mammal species with contrasting life
histories. We estimated adult lifespan, age at first reproduction,
breeding frequency and fecundity, and identified the main axes of
variation using Principal Component Analyses. The slow-fast continuum was
the main axis of life-history variation across species, but within
populations individual variation did not follow the slow-fast continuum in
any species. This suggests that individual life histories are neither slow
nor fast, but rather follow an idiosyncratic pattern across species
because of relative differences in the importance of processes such as
stochasticity, density dependence, and variation in individual
performance.