Oecologia (1992) 92:542-547 Oecologia 9 Springer-Verlag 1992 Distance effects on resource profitability and recruitment in the giant tropical ant, Paraponera clamta Jennifer H. Fewell*, Jon F. Harrison**, Tammy M. Stiller, and Michael D. Breed Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, CO 80309-0334, USA Received November 12, 1991 / Accepted in revised form August 6, 1992 Summary. We examine how cost and benefit components of resource profitability affect recruitment in the giant tropical ant, Paraponera clavata. To vary resource profitability, we changed the quantity of artificial nectar baits presented to foragers and the distance of nectar baits from the nest. Both distance to and amount of resource affected quantitative aspects of recruitment. At increased distances foragers were less likely to recruit, and fewer workers were recruited to the resource area. The amount of nectar affected the tendency of foragers to recruit, but had no effect on the number of ants recruited. Variation in resource distance was also asso- ciated with qualitative changes in recruitment strategy. Foragers at distant sites recruited from the canopy rather than from the nest, and often transferred nectar to other workers for transport to the nest. Nectar transfer and extra-nidal recruitment significantly reduced the time required for resource collection. It may also have in- creased the ability of workers to specialize in specific foraging tasks. A portion of the colony's foraging force specialized spatially by remaining in distant foraging areas without returning to the nest. The flexible recruit- ment system of P. clavata increases colonial net energetic gain rates by concentrating foraging effort on resources yielding the highest net energetic rewards, and increases the competitive abilities of individual colonies at resource sites by decreasing collection times. Key words: Foraging - Ants - Paraponera clavata Recruitment Social insects that recruit to resources have an advantage as central place foragers, because colonies can allocate foragers among food sites in ways that match resource profitability (Taylor 1978; Oster and Wilson 1978; *. ** Current address: Dept. of Zoology, Arizona State University, Tempe, AZ 85287-1501, USA Correspondence to: J.H. Fewell Stephens and Krebs 1986; Seeley 1986; Breed et al. 1987; Seeley and Visscher 1988). However, relatively little is known of how social insects integrate information on variation in resource benefit and collection costs, or of the relative importance of foraging cost in determining recruitment strategy. In this study, we examine how foragers of the giant tropical ant, Paraponera clavata, integrate information on foraging costs and benefits, and test whether they vary recruitment in response to changes in resource profitability. A number of studies have demonstrated that social insects, including ants, are able to assess food rewards. Many ant species adjust recruitment of nestmates to food resources in response to variation in food type, quantity and quality (H611dobler 1976; Taylor 1977; Crawford and Rissing 1983; Breed et al. 1987; Traniello 1989). The mechanisms by which they do so include: (1) variation in the number of pheromone trails or recruitment events (Wilson 1962; Verhaeghe 1982; Breed et al. 1987), and (2) variation in the intensity of motor displays or in pheromonal deposition within individual recruitment events (Szlep and Jacobi 1967; Hangartner 1969; Szlep- Fessel 1970; Cammaerts 1977; Traniello 1977; Jaffe and Howse 1979; Verhaeghe 1982). In contrast, little is known about how foraging costs affect recruitment systems. In an experimental context, ant colonies varied collection effort based on both caloric value of the resource and predation risk (Nonacs and Dill 1990). There is also limited evidence that time and/or energetic costs affect foraging decisions (H611dobler 1976; Taylor 1978; Fewell 1988). The foraging intensity of Pogonomyrmex colonies seems to decrease at food resources more distant from the nest (H611dobler 1976; Taylor 1978), but how ants achieve this response is still unclear. The ability to assess foraging costs is expected to benefit colonies if it allows foragers to preferentially recruit to resources that are highest in profitability, rath- er than only to resources that are highest in reward. We determine the mechanisms by which P. clavata vary re- cruitment in response to changing resource profitability, by presenting foragers with artificial nectar resources