Generation time: a reliable metric to measure life-history variation among mammalian populations.
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.
Gaillard
Jean-Michel
JM
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
Yoccoz
Nigel G
NG
Lebreton
Jean-Dominique
JD
Bonenfant
Christophe
C
Devillard
Sébastien
S
Loison
Anne
A
Pontier
Dominique
D
Allaine
Dominique
D
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