Search behavior and foraging ecology of the antFormica schaufussi: colony-level and individual patterns

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Abstract
Records of resource loads carried to the nest showed that foragers of the ant Formica schaufussi collect carbohydrate secretions and retrieve dead arthropods (chiefly insects) as the major components of the mixed diet feeding habit of this species. The foraging paths of workers collecting these resources were mapped in the field by marking the spatial coordinates (fixes) of an individual's position at 20-sec intervals. The frequency distribution of the azimuth of the fixes was significantly different from random, indicating that foraging activity is concentrated in certain directions around the nest. Ninety percent of all fixes were located within a radius of 5 m from the nest, a distance which is apparently equal to one-half the average nearest neighbor distance in a population of F. schaufussi colonies. Of the total number of foragers observed, a small proportion traveled with a high degree of linearity in one sector away from the nest; these workers were apparently involved in the collection of homopteran secretions. In contrast, the paths of other searching foragers were divisible into travel and local (area-restricted) search phases. Path analysis showed that movement during the travel phase was highly linear; during local search locomotion was characterized by a high rate of turning, and velocity was significantly lower. Variance in forager movement among paths was greater than variance within each path, suggesting that interindividual differences in search pattern are great. The spatial distribution of the points of onset of local search did not differ from random expectation, indicating that some ants may distribute their search effort according to the pattern of prey distribution. However, the foraging paths of workers collecting carbohydrate secretions seem to have little or no search component and thus represent an efficient mechanism to exploit a resource having a spatially predictable distribution.