Territory Area and Colony Size in the Fire Ant Solenopsis invicta

Abstract

1. The allometry of colony mass to territory area governs the total biomass of ants that a given habitat supports. This relationship serves as an important link between the performance of individual colonies and the behaviour of populations experiencing density-dependent competition for space. 2. Territory area, colony mass, and the numbers of ants of each caste and developmental stage, were measured for colonies of the fire ant Solenopsis invicta across a wide range of sizes. 3. Most of the variation in territory area was explained by colony size, measured either by worker number, worker biomass or colony biomass. 4. The nature of this relationship was linear in May, when colonies were near their annual minimum size, but non-linear in November, when they were near their annual maximum. Territories of a given size were occupied by larger colonies in November than May, probably because in this saturated population the simultaneous increase in worker number in all colonies occurred without room for territorial expansion. 5. Mound volume, which can be quickly measured without disturbing the colony, provided a reasonable estimate of colony or worker biomass and explained most of the variance in territory size.