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Capital and income breeding: the role of food supply.

Journal article
Authors Philip Stephens
Alasdair Houston
Karin C. Harding
Ian Boyd
John McNamara
Published in Ecology
Volume 95
Issue 4
Pages 882-896
ISSN 0012-9658
Publication year 2014
Published at Linnaeus Centre for Marine Evolutionary Biology (CEMEB)
Department of Biological and Environmental Sciences
Pages 882-896
Language en
Links dx.doi.org/10.1890/13-1434.1
Keywords marine mammals, energetics, life history optimization, dynamic programming
Subject categories Biological Sciences

Abstract

An aspect of life history that has seen increasing attention in recent years is that of strategies for financing the costs of offspring production. These strategies are often described by a continuum ranging from capital breeding, in which costs are met purely from endogenous reserves, to income breeding, in which costs are met purely from concurrent intake. A variety of factors that might drive strategies towards a given point on the capital-income continuum has been reviewed, and assessed using analytical models. However, aspects of food supply, including seasonality and unpredictability, have often been cited as important drivers of capital and income breeding but are difficult to assess using analytical models. Consequently, we used dynamic programming to assess the role of the food supply in shaping offspring provisioning strategies. Our model is parameterized for a pinniped (one taxon remarkable for the range of offspring strategies that it illustrates). We show that increased food availability, increased seasonality and, to a lesser extent, increased unpredictability can all favor the emergence of capital breeding. In terms of the conversion of energy into offspring growth, the shorter periods of care associated with capital breeding are considerably more energetically efficient than income breeding, because shorter periods of care are associated with a higher ratio of energy put into offspring growth, to energy spent on parent and offspring maintenance metabolism. Moreover, no clear costs are currently associated with capital accumulation in pinnipeds. This contrasts with general assumptions about endotherms, which suggest that income breeding will usually be preferred. Our model emphasizes the role of seasonally high abundances of food in enabling mothers to pursue an energetically efficient capital breeding strategy. We discuss the importance of offspring development for dictating strategies for financing offspring production.

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