ROLE OF FOOD-SUPPLY IN STRUCTURING A POPULATION OF FORMICA ANTS

1. In Elk Island National Park, Alberta, Canada, we studied the role of food supply in structuring a population of the ant Formica podzolica by examining the association between natural food levels and abundance, distribution and alate production of colonies, and comparing alate production of fed and unfed colonies. 2. Nest densities and reproductive output of colonies were greatest along forest edges, intermediate in grazed meadows and lowest in overgrazed meadows. These patterns among habitats were associated positively with natural food levels. 3. Colonies were dispersed uniformly on plots along forest edges, but dispersed either uniformly or randomly on plots in grazed and overgrazed meadows. 4. Females were larger than males, but size of neither males nor females differed significantly among habitats. Alate production was correlated positively with colony size. 5. Fed colonies in overgrazed meadows (the poorest habitat) produced significantly more sexuals within one reproductive cycle than those of unfed, control colonies, but not so compared to unfed colonies along forest edges (the best habitat). 6. We compare our experimental results with those of related studies of ants. In contrast to species that store food, we conclude that species storing relatively little food are more sensitive to changes in food supply, and respond to food addition in the short-term, even within one reproductive cycle.