| The major objective of this study was to integrate the individual and social foraging behaviors of an important insect granivore, the western harvester ant (Pogonomyrmex occidentalis), with characteristics of its native seed resources. Research was conducted in the sagebrush-steppe of southwestern Wyoming and consisted of three major components: a detailed analysis of the foraging patterns of individual workers, an evaluation of ant colony activity in space and time, and an assessment of native seed attributes that influence to the seed preferences of foraging ants.; Analyses of individual foraging behaviors showed ants to have distinct running and localized search behaviors. These behaviors could be described by site orientation and a correlated random walk, respectively. The directionality and velocity of searching ants progressively decreased from running to searching in intershrub spaces to searching under shrubs. Ants spent a greater proportion of total search time handling seeds in the undershrub compared to interspace patch types. Individuals also exhibited seed patch specializations, distance-dependent search effort, and differential seed species selection. Observations of ants along trunk trails, used as running paths of foragers, indicated exponential declines in the number of foragers with distance from the nest, seasonal variation in the use of trunk trails, and differences in the seed species composition among trails. Native seed preferences of P. occidentalis colonies under background and experimental conditions depended on seed size, seasonal abundance, and physical and nutritional attributes of seeds. Seed removal rates and recruitment of ant foragers to seed patches also depended on seed density. Harvester ants removed an estimated 1-12% of the total shrub-steppe soil seed pool. For preferred seed species, removal can be as high as 89%.; Results of the investigation suggest that a multi-leveled approach to studying the foraging behavior of this seed-eating, social insect is useful in elucidating the relationships of individual and colony behaviors, in evaluating some fundamental assumptions and predictions of foraging theory, and in determining the relationships of P. occidentalis with the shrub-steppe plant community. |
