Abstract
Desert seed-harvester ants, genus Pogonomyrmex, are central place foragers that search for resources collectively. We quantify how seed harvesters exploit the spatial distribution of seeds to improve their rate of seed collection. We find that foraging rates are significantly influenced by the clumpiness of experimental seed baits. Colonies collected seeds from larger piles faster than randomly distributed seeds. We developed a method to compare foraging rates on clumped versus random seeds across three Pogonomyrmex species that differ substantially in forager population size. The increase in foraging rate when food was clumped in larger piles was indistinguishable across the three species, suggesting that species with larger colonies are no better than species with smaller colonies at collecting clumped seeds. These findings contradict the theoretical expectation that larger groups are more efficient at exploiting clumped resources, thus contributing to our understanding of the importance of the spatial distribution of food sources and colony size for communication and organization in social insects.
Highlights
According to optimal foraging theory, an animal’s foraging behavior should maximize its net energy intake and minimize its costs [1,2]
We studied colonies from three sympatric Pogonomyrmex species that vary substantially in forager population size and asked how forager population size affects foraging rates for seeds in different spatial distributions
We focused on three sympatric species of desert seed-harvester ants in the genus Pogonomyrmex in the high desert of central New Mexico: P. desertorum, P. maricopa and P. rugosus
Summary
According to optimal foraging theory, an animal’s foraging behavior should maximize its net energy intake and minimize its costs [1,2]. The distribution of food affects how animals forage; many forage in groups when food is clumped and individually when food is more dispersed [3,4,5,6]. Ant foraging behaviors vary among species, ranging from largely independent foraging to mass recruitment. Foraging behaviors are affected by distribution of food [7,8] and colony size [3,9]. We use a field study to quantify how the distribution of food affects foraging rates in seed harvesting ants. We examine how the size of the forager population affects the relationship between food distribution and foraging rate
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