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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

View larger version (8K): [in a new window]   Fig. 1. Experimental design used to measure the metabolic rates of worker ants while foraging. Briefly, H2O- and CO2-free air was drawn through the respirometric chamber at a flow rate of 300 ml min–1 STP. The CO2 produced by the ant was measured by an IR CO2 analyzer and the data were stored in the computer.

View larger version (13K): [in a new window]   Fig. 2. Example of a respirometric record for a foraging ant at 1.18 µl min–1 and 30% sugar concentration food source. CO2 production rate (in µl h–1) is plotted as a function of time. There are three different parts: (1) before drinking (ca. 4 min), (2) while the ant drinking at the feeder (between arrows) and (3) after feeding (also ca. 4 min).

View larger version (9K): [in a new window]   Fig. 3. Feeding time (min) (A), crop load (mg) (B) and metabolic rates of foraging ants (µW) (C) as a function of five different nectar concentrations (1, 5, 10, 30 and 50%) and a flow-rate of 1.18 µl min–1. Values are means ± s.e.m. (N=13–17). Posteriori (Tukey test after one-way ANOVA): a,b, P<0.01; a,c and b,c, P<0.001; same letters do not differ significantly.

View larger version (12K): [in a new window]   Fig. 4. Feeding time (min) (A), crop load (mg) (B), and metabolic rates of foraging ants (µW) (C) as a function of three different flow rates (0.236, 1.18 and 2.36 µl min–1) and three different sugar solution concentrations (1, 5 and 30%). Values are means ± s.e.m. (N=6–17). Posteriori (Tukey test after first two-way ANOVA): a,b, P<0.01; a,c, P<0.001; same letters do not differ significantly. Posteriori (Tukey test after second two-way ANOVA: analysis differences between all concentration of 0.236 and 1.18 µl min–1, i.e. we did not take into account the 2.36 µl min–1 groups): for (A) 0.236 µl min–1 and 1% vs 0.236 µl min–1 and 5% or 30% (P<0.001), 0.236 µl min–1 and 5% or 30% vs 1.18 µl min–1 and 1% (P<0.001); for (B) 0.236 µl min–1 and 1% vs 1.18 µl min–1 and 5% or 30% (P<0.001), 1.18 µl min–1 and 1% vs 1.18 µl min–1 and 30% (P<0.001); for (C) 0.236 µl min–1 and 1% vs 1.18 and 30% (P<0.05).

View larger version (14K): [in a new window]   Fig. 5. Instantaneous metabolic rates (µW) as a function of crop load expressed in mass (1, 3, 5 and 7 mg) at three different flow rates (0.236, 1.18 and 2.36 µl min–1). Values are means ± s.e.m. (N=3–17).

View larger version (6K): [in a new window]   Fig. 6. Relation of energy losses and gains expressed in µW for different nectar flow-rates and concentrations. Energy expenditures are measured metabolic rate of ant workers and the energy gain is calculated from the sucrose concentration and flow rate delivery of sugar solution from the artificial feeder. (a) 0.236 µl min–1 flow rate and 1% sucrose concentration, (b) 1.18 µl min–1 and 1%, (c) 0.236 µl min–1 and 5%, (d) 1.18 µl min–1 and 5%, (e) 0.236 µl min–1 and 30%, (f) 2.36 µl min–1 and 5%, (g) 1.18 µl min–1 and 10%, (h) 1.18 µl min–1 and 30%, (i) 1.18 µl min–1 and 50%, and (j) 2.36 µl min–1 and 30%. Note the logarithmic scale of the x-axis.

View larger version (7K): [in a new window]   Fig. 7. Relation of the possible maximum distance (km) traveled by a forager with the energy gained in a foraging trip. Energy gained is a function of volume of crop load and concentration of the sugar solution.