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The effect of thermoregulatory substitution on optimal energy reserves of small birds in winter
Author(s) -
M. McNamara John,
Ekman Jan,
I. Houston Alasdair
Publication year - 2004
Publication title -
oikos
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.672
H-Index - 179
eISSN - 1600-0706
pISSN - 0030-1299
DOI - 10.1111/j.0030-1299.2004.12188.x
Subject(s) - substitution (logic) , energy expenditure , predation , ecology , thermoregulation , biology , environmental science , endocrinology , computer science , programming language
Previous models have predicted the body mass of small birds in winter on the basis of a trade‐off between starvation and predation. Many of these models have assumed that energy expenditure while active increases with body mass. The implications of the fact that the metabolic cost of activity can substitute for internal heat production and help keep the bird warm have not been investigated. In this paper we show that if thermoregulatory substitution occurs then there is a critical level of energy reserves above which an active bird is thermoneutral. This critical level increases as temperature decreases. Below this level, substitution of energy results in higher optimal levels of reserves than would be predicted in the absence of substitution. Our model thus predicts that at low temperatures body mass will be higher when thermoregulatory substitution occurs.