How resources and encounters affect the distribution of foraging activity in a seed-harvesting ant

We examined how the foraging ecology of the seed-harvesting ant Messor andr ei depends upon the distribution of resources and the presence of conspecif ics. Bait experiments showed that colonies can recruit to high-density patc hes of seeds. However, at the seasonal scale, natural resource distribution did not affect the distribution of foraging activity. We conducted the stu dy in years of high rainfall and thus seed availability may not have been a limiting factor. Colonies always preferred to forage in areas closer to th eir nest, which may reduce travel time between the nest and foraging sites. On a day-to-day scale, encounters between neighboring colonies at a site i ncreased the probability that colonies would return to forage at that site; this was true both for natural and experimental encounters. In the summer, this resulted in colonies foraging at the sites of intraspecific encounter s on more days than in areas where no encounter had occurred. Encounters be tween colonies included fighting, and there was little overlap between the foraging areas of neighboring colonies: both results suggest that one funct ion of encounters is to defend foraging space. The high probability of retu rn to the site of an encounter between colonies suggests that encounters ma y have a second function: to indicate the presence of resources.