Spatial Model of Movement and Foraging in Harvester Ants (Pogonomyrmex) (I): The Roles of Memory and Communication

To evaluate the relative importance of memory and pheromone trails to seed foraging, we constructed an individual-based model of ant foraging for a colony of the western harvester ant Pogonomyrmex occidentalis, a central-place forager. The model simulates the dynamic spatial positions of all individuals of three classes: ants without seeds, ants with seeds, and seeds. Each ant foraging above-ground is moved in a non-stationary correlated random walk according to a set of rules that determine the direction and distance of each successive step. We used movement rules that hypothesized behavioral mechanisms in five general areas: (i) space perception, (ii) memory, (iii) chemical communication, (iv) physiological competence of sensory systems, and (v) stimulation of nestmates. Field experiments that manipulated seed densities were simulated by depositing model seeds in patches at different times and places during the simulation. ulated experimental presentations of renewing seed patches using several different movement rules and mechanisms of chemical communication. When pheromones were laid on a trail to the nest the best models had rules in which (i) ants used memory, (ii) foragers were stimulated at the nest by successful ants, and (iii) the interval between pheromone deposits was small. Models without any one of these three components failed to predict correctly. Sensitivity analyses indicated that ant foraging abilities were not strongly affected by chemical properties of the pheromone, but were influenced by the frequency of pheromone deposition and the geometry of the nest opening.