• colony size;
  • density dependence;
  • mortality;
  • seed-eating ants

1.  This study investigates how the density and size of conspecific neighbours affected the mortality of established colonies. Data were from a population of 250–300 colonies of the red harvester ant [Pogonomyrmex barbatus (F. Smith)], on a 10-ha site, from 1988 to 1995.

2.  Colonies are more likely to die as they grow older.

3.  Small neighbours tend to lower the probability of dying.

4.  The probability of dying varied significantly from year to year.

5.  There was little effect of crowding on mortality.

6.  There appeared to be no spatial effects, on the scale of 25. m, on the probability of dying.

7.  Previous work shows effects of density on the founding of new colonies and on the reproductive output of established ones. The results presented here indicate that competition with neighbours rarely causes the death of established colonies.