A field assessment of optimal foraging in ants: trail patterns and seed retrieval by the European harvester ant Messor barbarus.

摘要

The foraging ecology of Messor barbarus, a major seed predator on annual grasslands of the Mediterranean area, is related to resource availability. Several predictions of optimal foraging theory under natural conditions of seed harvesting were alsoaddressed in the study held at Vidauban, France. Spatial patterns of foraging trails tended to maximize acquisition of food resources, as trails led the ants to areas where seeds were more abundant locally. Moreover, harvesting activity concentrated on highly frequented trails, on which seeds were brought into the nest in larger numbers and more efficiently, at a higher mean rate per worker. The predictions of optimal foraging theory that ants should be more selective in both more resource-rich and moredistant patches were tested in the native seed background. The selectivity of ants was positively related to trail length and thus to distance from the nest of foraged seeds. Conversely, no consistent relationship between selectivity and density or species diversity of seed patches was found. Selectivity assessed at the colony level may depend on factors other than hitherto reported behavioural changes in seed choice by individual foragers.