Social structure of Gnamptogenys bisulca (Formicidae: Ectatomminae) in tropical forests

Abstract

The study of the social organization of ants may help to understand why some species are able to persist in natural forests after fragmentation and anthropogenic disturbances. The Neotropical ant Gnamptogenys bisulca has shown to be a biological indicator of habitat quality in Andean montane forests and we proposed to explain this characteristic by investigating its social structure and the spatial distribution of colonies at fine scale. In eight 100 m2 plots located in four forests in the western Colombian Andes, the position of G. bisulca colonies was recorded for spatial distribution and their social composition described: ergatoid females were found in most of the nests, isolated or together with normal queens. As ergatoids and queens were dissected to examine their reproductive status, it appeared that apparent polygyny represented, in fact, effective monogyny, with other potential reproductive females being unmated or inhibited. In the few cases of mixed colonies, a queen was always at the head of the colony. Local spatial distribution was random and did not fit the hypothesis of nesting by fission, as generally observed in the case of the presence of ergatoids. However, the social structure was significantly different according to the site, the most preserved forest showing no or rare ergatoids (but queens) compared to the other sites. Our results indicated that the presence of ergatoids in G. bisulca may help colonies to adapt to slightly disturbed habitat contexts.