SPATIAL-DISTRIBUTION OF POGONOMYRMEX OCCIDENTALIS - RECRUITMENT, MORTALITY AND OVERDISPERSION

1. The western harvester ant Pogonomyrmex occidentalis is frequently the dominant insect species in the deserts and arid grasslands of western North America. 2. The lek mating system of this species provides an opportunity to relate local reproduction to dispersal. Because reproductives from individual colonies aggregate at a limited number of sites for mating, there is a small number of propagule sources. 3. We studied the spatial distribution of a large population of this species. The population as a whole was highly overdispersed, although the patterns of recruitment were highly clumped and correlated in 2 years. 4. In addition to recruitment limitation, we also found evidence of space limitation in the population. Mortality rates were related to the nearest neighbour distance, even when taking into account the fact that small colonies have higher mortality. 5. The spatial structure of the population developed along with the age structure of the population, and was a complex product of the production of new queens, the availability of recruits and the availability of space.