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First published online October 5, 2006
Journal of Experimental Biology 209, 4091-4101 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02478

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Foraging energetics of a nectar-feeding ant: metabolic expenditure as a function of food-source profitability

Pablo E. Schilman^* and Flavio Roces

Theodor-Boveri-Institut der Universität Würzburg, Lehrstuhl für Zoologie II, Biozentrum, Am Hubland, D-97074 Würzburg, Germany

^* Author for correspondence at present address: University of California at San Diego, Division of Biological Sciences, Mail code 0116, 9500 Gilman Drive, La Jolla, CA 92093-0116, USA (e-mail: pschilman{at}yahoo.com)

Accepted 8 August 2006

We examined the quantitative relationship between the energetic costs and benefits of nectar collection by nectar-feeding ants, Camponotus rufipes. In the laboratory, individual workers were trained to visit an artificial feeder that provided a sucrose solution of 1%, 5%, 10%, 30% or 50% at controlled flows, in a similar span range to those observed in natural nectar sources. We measured foraging times, nectar loads collected, and CO₂ production during actual feeding, as an indication of the energy expenditure for a single forager. Results show an increase in individual metabolic rates with increasing flow rate of sugar solution, but no dependence on sucrose concentration. This increase in metabolic expenditure does not depend on the crop load attained while feeding, as intuitively expected, and is therefore a result of an increased activity brought about by the food-source profitability experienced by the forager. The energy gained during collection of sugar solution is always higher than the energy spent by the ant. Even with a food source of lower quality than a natural source, the ants gain ca. tenfold of what they spend. Based on a simplified model, we calculated that foragers of C. rufipes could travel from 0.5 to 9 km with the energy gained in a single foraging trip only. These results suggest that decreasing foraging time is more important than increasing individual energetic efficiency when workers of the nectar-feeding ant C. rufipes decide to stop drinking and return to the nest with partial crop loads.

Key words: Camponotus rufipes, central-place foragers, metabolic rate, nectar feeding

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