Abstract
Solitary foragers can balance demands for food and safety by varying their relative use of foraging patches and their level of vigilance. Here, we investigate whether colonies of the ant, Formica perpilosa, can balance these demands by dividing labor among workers. We show that foragers collecting nectar in vegetation near their nest are smaller than are those collecting nectar at sites away from the nest. We then use performance tests to show that smaller workers are more likely to succumb to attack from conspecifics but feed on nectar more efficiently than larger workers, suggesting a size-related trade-off between risk susceptibility and harvesting ability. Because foragers that travel away from the nest are probably more likely to encounter ants from neighboring colonies, this trade-off could explain the benefits of dividing foraging labor among workers. In a laboratory experiment, we show that contact with aggressive workers results in an increase in the mean size of recruits to a foraging site: this increase was not the result of more large recruits, but rather because fewer smaller ants traveled to the site. These results suggest that workers particularly susceptible to risk avoid dangerous sites, and suggest that variation in worker size can allow colonies to exploit profitably both hazardous and resource-poor patches.
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Acknowledgments
We thank David Holway, Jennifer Fewell, and the Social Insect Research Group at Arizona State University for helpful comments on the manuscript. Several anonymous reviewers also provided helpful comments. We also thank the staff at the Southwestern Research Station for assistance, and the Statistical Consulting Service at the University of Minnesota for advice. Glen Needham kindly provided use of a microbalance. The experiments comply with the current laws of the United States.
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Kay, A., Rissing, S.W. Division of foraging labor in ants can mediate demands for food and safety. Behav Ecol Sociobiol 58, 165–174 (2005). https://doi.org/10.1007/s00265-005-0914-x
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DOI: https://doi.org/10.1007/s00265-005-0914-x