NEST-SITE LIMITATION AND COLONY TAKEOVER IN THE ANT LEPTOTHORAX-NYLANDERI

Ecological constraints on the success of independent colonies are thou ght to strongly shape the organization of ant societies. One of the mo st important factors is probably the availability of suitable empty ne st sites. By population censuses, laboratory experiments, and microsat ellite analyses, we investigated the colony and population structure o f the small, myrmicine ant Leptothorax (Myrafant) nylanderi in a decid uous forest near Wurzburg, Germany, where nest sites appear to be stro ngly limited, especially in late summer. Colonies of L. nylanderi inha bit cavities in rotting branches, hollow acorns, grass stems, etc. Aft er hibernation, a temporary overabundance of empty nest sites facilita tes the fragmentation of larger colonies into smaller buds, which, bec ause the species is monogynous, are in part queenless. Nest sites beco me scarce in summer due to rapid decay, and both established colonies and young founding queens face a severe shortage of suitable nest site s. This leads to the fusion of established, unrelated colonies, which after initial fighting permanently merge and live together. Typically only one queen survives after fusion. Similarly, young mated queens ma y seek adoption in alien nests instead of founding their own colonies solitarily, and here again only a single queen survives. This temporar y intraspecific parasitism may be an important first step in the evolu tion of obligatory permanent parasitism, which is widespread in the ge nus Leptothorax.