Evol Ecol Res 4: 749-758 (2002)     Full PDF if your library subscribes.

Reproductive effort, offspring size and benefit–cost ratios in the classification of life histories

Eric L. Charnov*

Department of Biology, The University of New Mexico, Albuquerque, NM 87131-1091 and Department of Zoology, Oregon State University, Corvallis, OR 97331, USA

Address all correspondence to Eric Charnov, Department of Biology, The University of New Mexico, Albuquerque, NM 87131-1091, USA.


There have been many attempts to document links between reproductive allocation and factors such as adult body size and demography. This paper suggests that among closely related taxa, two dimensionless numbers, each a benefit–cost ratio summarizing reproductive timing, allocation and demography, are invariants and thus are useful to classify life histories. The two numbers are E/α and C · E, where E is average adult life span, α is age-at-first-reproduction and C is average mass (per adult) devoted to reproduction per unit of time, divided by the average adult body mass (m); C is usually called ‘reproductive effort’. Since E−1 is the average adult mortality rate, C/E−1 is the reproductive effort (benefit) per unit death (cost). Similarly, E/α is the amount of time for reproduction (E) divided by the time cost to get there (α). Combining these two numbers with the relative size (I ) of an offspring (I/m) yields a new classification scheme for life histories; this is contrasted with other classification schemes (e.g. r and K ).

Keywords: classification of life histories, dimensionless numbers, life-history cube, r and K selection, Smith–Fretwell.

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        © 2002 Eric L. Charnov. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.

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