Reproductive dispersion and damping time scale with life-history speed

Abstract

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 ( $T_c$ ) is known to capture aspects of life-history variation, such as life-history speed, does $T_c$ also determine reproductive dispersion ( $S$ ) or damping time ( $\tau$ )? Using phylogenetically corrected analyses on 633 species of animals and plants, we find, firstly, that reproductive dispersion $S$ scales isometrically with $T_c$ . Secondly, and unexpectedly, we find that the damping time ( $\tau$ ) does not scale isometrically with generation time, but instead changes only as $T_c^b$ with $b<1$ (also, there is a similar scaling with $S$ ). 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.

Keywords: biological time; damping time; generation time; life history; reproductive dispersion.