Reproductive dispersion and damping time scale with life-history speed

Iteroparous species may reproduce at many different ages, resulting in a reproductive dispersion that affects the damping of population perturbations, and varies among life histories. Since generation time (Tc$$ {T}_c $$) is known to capture aspects of life-history variation, such as life-history speed, does Tc$$ {T}_c $$ also determine reproductive dispersion (S$$ S $$) or damping time (tau$$ \tau $$)? Using phylogenetically corrected analyses on 633 species of animals and plants, we find, firstly, that reproductive dispersion S$$ S $$ scales isometrically with Tc$$ {T}_c $$. Secondly, and unexpectedly, we find that the damping time (tau$$ \tau $$) does not scale isometrically with generation time, but instead changes only as Tcb$$ {T}_c<^>b $$ with b<1$$ b (also, there is a similar scaling with S$$ S $$). This non-isometric scaling implies a novel demographic contrast: increasing generation times correspond to a proportional increase in reproductive dispersion, but only to a slower increase in the damping time. Thus, damping times are partly decoupled from the slow-fast continuum, and are determined by factors other than allometric constraints.