EFFECTS OF PREDICTABILITY AND COMPETITION ON GROUP AND INDIVIDUAL CHOICE IN A FREE-RANGING FORAGING ENVIRONMENT LAVINIA TAN,FRANK SOSA,ERIC TALBOT,DONALD BERG,DAWNIRIS EVERSZ, AND TIMOTHY D. HACKENBERG REED COLLEGE The present study examined the social foraging of rats in an open arena. The relative quantity of food varied across two food sources, or “patches.” Five food quantity ratios (1:1, 1:2, 1:8, 8:1, 2:1) were presented in a series of 30-min sessions. Ratios varied randomly across 6-min components within sessions (Phase 1), or in a consistent order across sessions (Phase 2). Group and individual preferences were well described by the ideal free distribution and the generalized matching law, respectively, with evidence of undermatching at both group and individual levels. Sensitivity of individual and collective behavior to the relative quantities of food was higher in Phase 2 than in Phase 1. Competitiveness rankings, assessed before and after experimental sessions by delivering food in rapid succession from a single feeder, was positively related to sensitivity values in Phase 1, but less consistently so in Phase 2. This study illustrates a promising experimental method for investigating foraging in a social context. Key words: choice, foraging, concurrent schedules, generalized matching law, ideal free distribution Adaptive decision-making requires tradeoffs between various costs (e.g., time, energy, oppor- tunity, predation risk) and benefits (e.g., caloric gain, mating opportunities), both immediate and deferred. Optimal foraging models are quantita- tive characterizations of these costs and benefits (see Stephens & Krebs, 1986), and have been highly successful in characterizing various aspects of foraging in a wide range of species and settings (e.g. Biernaskie, Walker, & Gegear, 2009; Burke & Montevecchi, 2009; Doniol-Valcroze, Lesage, Giard, & Michaud, 2011; Edouard, Fleurance, Dumont, Baumont, & Duncan, 2009; Hernández & Laundré, 2005; de Knegt, Hengeveld, van Langeveld, de Boer, & Kirkman, 2007; Suraci & Dill, 2013; Wajnberg, Bernhard, Hamelin, & Boivin, 2006; also see Kennedy and Gray, 1993; Pyke, 1984; Stephens & Krebs, 1986; Stephens, Brown, & Ydenberg, 2007; Tregenza, 1995 for reviews). While the majority of models to date have focused on the behavior of individual foragers, many species forage in social contexts (e.g. Abrahams, 1989; Amano, Ushiyama, Moriguchi, Fujita, & Higuchi, 2006; Dreisig, 1995; Grand, 1997; Harper, 1982; Humphries, Ruxton, & Metcalfe, 1999; Inman, 1990; Kohl- mann & Risenhoover, 1997; Kurvers et al., 2010; Michelena, Sibbald, Erhard, & McLeod, 2008; Pulido & Diaz, 1997). A better understanding of how foraging behavior affects, and is affected by, social context is thus of great theoretical importance. The most successful model of social foraging to date is known as the Ideal Free Distribution (IFD). Originally formulated by Fretwell and Lucas (1970), this model predicts the distribu- tion of animals will match the distribution of available resources among different patches, according to the following simple rule: N 1 N 2 ¼ R 1 R 2 ; ð1Þ where N ¼ the number of foragers, R ¼ the number of resource items (reinforcers), and the subscripts represent the two alternatives. Despite the simplicity of the model, and the complexity of the social situations it encompasses, the IFD provides a good quantitative description of group behavior in a range of species, including birds (pigeons: Baum & Kraft, 1998; Bell & Baum, 2002; common cranes: Bautista, Alonso, & Alonso, 1995; sparrows: Gray, 1994; and mallards: Harper, 1982), fish (guppies: Abrahams, 1989; Coho salmon: Grand, 1997; and cichlids: Grand & Grant, 1994; Tregenza & Thompson, 1998), invertebrates (wood ants: Lamb & Ollason, 1993; Research support by NIDA Grant R01 DA026127. Some of these data were presented previously at the 2012 meetings of the Southeastern Association for Behavior Analysis and the Society for the Quantitative Analysis of Behavior, and the 2013 meeting of the Association for Behavior Analysis- International. The authors thank Greg Wilkinson for technical support, as well as Maha Pasha and Shruti Korada for their assistance with data analysis. Address correspondence to Lavinia Tan, Psychology Department, Reed College, 3203 SE Woodstock Blvd., Portland OR 97202 (email: ltan@reed.edu). doi: 10.1002/jeab.76 JOURNAL OF THE EXPERIMENTAL ANALYSIS OF BEHAVIOR 2014, 101, 288–302 NUMBER 2 (MARCH) 288