Effect of habitat structure on ant assemblages associated to two pioneer tree species (Hymenoptera : formicidae).

Abstract

The present study investigates the effects of ant species distributions among host tree crowns in response to surrounding habitat. It was developed at the State Park of Rio Doce, in the middle basin of the Doce river, South Eastern Brazil. The studied plants were Mabea fistulifera Mart. (Euphorbiaceae), a forest border ecotone pioneer species, and Byrsonima sericea DC. (Malphigiaceae), a forest-lake ecotone colonizer species. Ants were sampled on the tree crowns for using a beating device, during one dry and two wet seasons thus comparing ecotone and interior forest habitats. In total 335 ant individuals were collected belonging to 5 subfamilies, 15 genera and 40 species. A MANOVA model shows differences in species richness only for the wet season of 2001, where the mean number of ant species per tree was nearly double in the ecotones than in the forest, regardless of which host plant. Ant abundance did not differ between habitats (ecotone and forests), but Mabea fistulifera had, on average, three times more ant individuals on its crown than B. sericea in the wet season of 2001. In addition, this value found for M. fistulifera was higher than any other overall abundance estimate in the following dry or wet season. A discriminant analysis showed how the ant fauna composition was distinct in the artificial ecotone site between sampling periods, which demonstrate how a disturbance can modify the ant species composition in comparison with preserved habitats. However, the ant fauna on M. fistulifera in the interior forest and on B. sericea in the ecotone were more similar than any other sub-set of species, suggesting that micro-habitat ecological conditions and geological history could influence more ant species distribution than host plant or ecotone-interior contrasts.