DISPERSAL FOR SURVIVAL: SOME OBSERVATIONS ON THE TRUNK ANT (<I>FORMICA TRUNCORUM</I> FABRICIUS)

Abstract

The survival chance of the trunk ant (Formica truncorum) is compared with the survival chance of two other species of red wood ants: F. rufa and F. polyctena. Nest populations of F. truncorum are much smaller than nest populations of the other red wood ant species, which makes the species a weaker competitor. Moreover, F. truncorum has to move more often, as its nests are small and untidily built, which makes the species more dependent on external heat for raising its brood. In order to survive, the greater extinction chance of F. truncorum should be compensated by a greater colonization chance. The colonization chance depends on the number of queens produced, their chance of becoming fertilized and their chance of becoming adopted by F. fusca. It appeared that nest populations of F. truncorum produced less sexuals than those of the other red wood ant species, while there are no good arguments to assume that their queens will have a greater chance of becoming fertilized or that the queens are more skillful in finding a suitable nesting place. It is argued that local populations of the trunk ant are more prone to extinction than those of F. polyctena and F. rufa, at least in the sandy areas of west and central Europe, where most F. truncorum colonies are monodomous and largely also monogynous. So F. truncorum queens should have a greater chance to become adopted by F. fusca than F. rufa and F. polyctena. Adoption experiments can solve this problem.