Abstract
New World army ants (Ecitoninae) are nomadic group-predators that are widely thought to have a substantial impact on their prey. Nevertheless, quantitative data on prey intake by army ants is scarce and mostly limited to chance encounters. Here, I quantify the prey intake of the army ant Eciton hamatum at the contrasting scales of raid, colony (sum of simultaneous raids), and population. Like most army ants, E. hamatum conducts narrow ‘column raids’ and has a specialized diet of ant prey. I show that individual raids often had periods of no prey intake, and raid intake rates, calculated in g/min, differed significantly among colonies. Moreover, neither mean nor peak raid intake rates were correlated with colony size. Similarly, colony intake rates differed significantly among colonies, and mean colony intake rates were not correlated with colony size. However, mean colony intake rates were significantly higher than mean raid intake rates, and peak colony intake rate was correlated with colony size. Having multiple raids thus improves colony-level intake rates, and larger colonies can harvest more prey per unit time. Mean colony intake rate across colonies was 0.067 g/min dry weight and mean daily colony intake was calculated at 38.2 g. This intake is comparable to that of Eciton burchellii, which has a more generalized diet and conducts spectacular ‘swarm raids’ that are seen as having a greater impact on prey than column raids. Population size on Barro Colorado Island, Panama, was estimated to be 57 colonies, which extrapolates to a daily population intake of nearly 2 kg of prey dry weight, or 120 g/km2. Broadly, these findings demonstrate that column raiding army ants experience considerable variation in prey intake for individual raids, but can still achieve notable impact at the larger scales of colony and population. Furthermore, they challenge the idea that swarm-raiding species necessarily have greater intake and thus impact on prey. Instead, I suggest that conducting multiple column raids may be a strategy that allows for comparable intake from a more specialized diet.
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Acknowledgments
This manuscript is dedicated to Carl W. Rettenmeyer. His positive influence on my career and life are immeasurable. I also thank Ellie Clark, Egbert G. Leigh Jr., and William T. Wcislo for valuable discussion, as well as the staff of the Smithsonian Tropical Research Institute for logistical support. This research was funded primarily by a Short-Term Fellowship from the Smithsonian Tropical Research Institute, Panama, with additional support from Carl Rettenmeyer.
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Powell, S. How much do army ants eat? On the prey intake of a neotropical top-predator. Insect. Soc. 58, 317–324 (2011). https://doi.org/10.1007/s00040-011-0152-3
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DOI: https://doi.org/10.1007/s00040-011-0152-3