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Summary: Energetics, cost reduction and functional
consequences of sh morphology
Lars B. Pettersson*
{ and Anders HedenstrÎm
Department of Ecology, Ecology Building, SE-223 62 Lund, Sweden
Cost reduction strategies are often invoked as explanations when studies of adaptation fail to ¢nd
predicted costs. This might seem discouraging, o¡ering little opportunity for further investigation. In this
paper, we demonstrate that cost reduction strategies can themselves be investigated by arguments from
design. Recent work on inducible morphological defences has shown that hydrodynamical disadvantages
(e.g. high drag) in ¢shes can be compensated for by standard metabolic rate (SMR) adjustments. Here,
we theoretically investigate the possibilities and limitations for swimming cost compensation through
SMR adjustment. We continue by modelling how intraspeci¢c power curve variation a¡ects the optimal
swimming velocity between food patches. Our results show that, even though SMR modi¢cations may
compensate for hydrodynamical disadvantages, low-drag ¢shes will nevertheless have a marked advan-
tage under high food abundance. The relative advantage will decrease with decreasing food levels. We
also show that hydrodynamical properties of ¢shes can be used to predict their propensity to become fora-
ging (or swimming) specialists. Low-drag ¢shes can use a broad range of swimming velocities without
substantial increases in swimming cost, whereas the cost of deviating from the optimal swimming velocity
increases markedly in high-drag ¢shes. The results have important implications for the evolution of
morphological diversity in ¢shes.
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