Maria Phelps

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


A number of field studies, conducted with birds, have found that dominant birds aggress against subordinate birds to attain priority of access to food. However, the level of aggression exhibited by dominant birds varied in accord with a cost-benefit analysis of the physical properties and spatial organization of the resource base. When the costs of aggression exceeded the benefits gained from resource defense, dominant birds decreased the level of aggression. Because rats also forage in groups and form functional social hierarchies, it was predicted that dominant rats, like dominant birds, would decrease aggression as a function of three resource attributes. The effect of food size, food density and food distribution on the foraging and agonistic behavior of pairs of dominant and subordinate rats (Rattus norvegicus) was examined in a series of three experiments.;Prior to resource attribute testing, dominance was determined in a dominance wedge. In each experiment, the foraging behavior of rats was observed under both isolate-testing and paired-testing conditions. The patch-testing apparatus consisted of two rectangular patches, each containing multiple feeders. In Experiment 1, the size of individual food items was varied. In Experiment 2, the density of food in patches was manipulated. In Experiment 3, the spatial distribution of food items was manipulated.;Dominant rats spent comparatively more time in aggression when food items were large, food density was high and food was clumped. Consequently, under these conditions, subordinate rats obtained less food items, exhibited lower feeding rates, and lost more session time to agonistic behavior during paired-testing than dominant rats. Both ranks exhibited higher mean search rates and lower handling times in paired-testing than during isolate-testing. Subordinate rats were more likely than dominant rats to alter the location of consumption during paired-testing. Aggression also suppressed the subordinate's foraging activity as measured by cumulative number of feeders visited and food items encountered.;Thus, dominant laboratory rats, like dominant birds, use aggression to attain priority of access to food. Moreover, the level of aggression varied as a function of the resource attributes and decreased when such behavior detracted from the benefits gained from resource defense.



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