title: Generation time: a reliable metric to measure life-history variation among mammalian populations.
abstract: Oli and Dobson proposed that the ratio between the magnitude and the onset of reproduction (F/ alpha ratio) allows one to predict the relative importance of vital rates on population growth rate in mammalian populations and provides a reliable measure of the ranking of mammalian species on the slow-fast continuum of life-history tactics. We show that the choice of the ratio F/ alpha is arbitrary and is not grounded in demographic theory. We estimate the position on the slow-fast continuum using the first axis of a principal components analysis of all life-history variables studied by Oli and Dobson and show that most individual vital rates perform as well as the F/ alpha ratio. Finally, we find, in agreement with previous studies, that the age of first reproduction is a reliable predictor of the ranking of mammalian populations along the slow-fast continuum and that both body mass and phylogeny markedly influence the generation time of mammalian species. We conclude that arbitrary ratios such as F/ alpha correlate with life-history types in mammals simply because life-history variables are highly correlated in response to allometric, phylogenetic, and environmental influences. We suggest that generation time is a reliable metric to measure life-history variation among mammalian populations and should be preferred to any arbitrary combination between vital rates.
authors.affiliation: Unité Mixte de Recherche 5558, Biométrie et Biologie Evolutive, Bâtiment 711, Université Claude Bernard Lyon 1, 43 boulevard du 11 novembre 1918, 69622 Villeurbanne Cedex, France. gaillard@biomserv.univ-lyon1.fr
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Gaillard
authors.forename: Nigel G
authors.initials: NG
authors.lastname: Yoccoz
authors.forename: Jean-Dominique
authors.initials: JD
authors.lastname: Lebreton
authors.forename: Christophe
authors.initials: C
authors.lastname: Bonenfant
authors.forename: Sébastien
authors.initials: S
authors.lastname: Devillard
authors.forename: Anne
authors.initials: A
authors.lastname: Loison
authors.forename: Dominique
authors.initials: D
authors.lastname: Pontier
authors.forename: Dominique
authors.initials: D
authors.lastname: Allaine
mesh_terms: D000375:Aging; D000818:Animals; D001835:Body Weight; D005260:Female; D008297:Male; D008322:Mammals / Q000033:anatomy & histology / Q000502:physiology*; D008954:Models, Biological; D010802:Phylogeny; D011157:Population Dynamics; D012098:Reproduction / Q000502:physiology*; D013997:Time Factors