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Behavioral Ecology Advance Access published online on November 23, 2006
Behavioral Ecology, doi:10.1093/beheco/arl080
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© The Author 2006. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org
Received March 27, 2006
Revised October 10, 2006
Accepted October 16, 2006

Article

Capital or income breeding? A theoretical model of female reproductive strategies

Alasdair I. Houston 1, Philip A. Stephens 2 *, Ian L. Boyd 3, Karin C. Harding 4, and John M. McNamara 2

1 School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG, UK
2 Department of Mathematics, University of Bristol, University Walk, Bristol, BS8 1TW, UK
3 Sea Mammal Research Unit, Gatty Marine Laboratory, University of St Andrews, St Andrews, Fife, KY16 8LB, UK
4 Department of Marine Ecology, Göteborg University, Box 461, 405 30 Göteborg, Sweden

* To whom correspondence should be addressed.
Philip A. Stephens, E-mail: philip.stephens{at}bristol.ac.uk


  Abstract

Energy storage is an important component of life-history variation. A distinction is recognized between species that provision offspring using energy gained concurrently (income breeders) and those that provision offspring using energy stores accumulated at an earlier time (capital breeders). Although this distinction has been recognized for some time, surprisingly little attention has been paid to the general adaptive value of the 2 strategies. Here, we present a simple, general framework for modeling female reproductive strategies. We show that our framework can be applicable either to annual breeders that aim to maximize the energy delivered to their offspring before independence, or to species with shorter reproductive cycles that aim to maximize reproductive rate, given that their offspring must build up a given level of reserves before independence. For both scenarios, we show that the costs of accumulating capital can lead to pure income breeding, pure capital breeding, or a mixture of the 2 strategies. Our model allows the effects of a variety of parameters to be assessed. Length of gestation, offspring metabolism, efficiency of energy transfer from mother to offspring, and the relative rates of energy gain by females with and without offspring are all important factors. The cost associated with accumulated capital is a particularly critical determinant of the strategy adopted. More detailed approaches to specific systems may provide a greater understanding of the factors promoting different maternal strategies for offspring provisioning.

Keywords: blubber; energy storage; lactation; mass-dependent costs; optimal behavior.
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