A rainforest ant mosaic: The edge effect (Hymenoptera : Formicidae)

The ant mosaic in the edge of a Cameroonian rainforest was studied along 50 0m of a dirt road in order to compare it to that of the canopy in the same forest (Dejean et al. 2000; 167 trees studied). The plant species diversity was low (369 plant individuals belonging to 48 species and 28 families). T he Euphorbiaceae Alchornea cordifolia was the most frequent species. The an t assemblage was characterized by high abundance but low diversity (22 spec ies in total) with eight "dominant" species, and seven sub-dominant as well as non-dominant species. The dominant species occupied only 69.9% of the p lants. The most frequent species, Crematogaster striatula, Pheidole megacep hala Oecophylla longinoda, and Tetramorium aculeatum occupied 25.5%, 18.2%, 13%, and 9.2% of the plants, respectively. Among the sub-dominant species, Camponotus brutus was by far the most frequent ( 12.2% of the plants). The associated homopterans recorded on 30.6% of the plants belonged to eight f amilies with Stictococcidae and Membracidae being the most frequent. As a r esult, the main differences with the canopy of the same forest consisted in a lower plant diversity, more dominant ant species (eight vs, four), a lar ger diversity and greater influence of sub-dominant species (4.8% of the tr ees vs. 24.7% of the plants), and a larger diversity of attended Homoptera, including Aphids and Pseudococcids among the Sternorrhyncha, and several f amilies of Auchenorrhyncha absent or very rare if present at canopy level. Differences in the microhabitat requirements of dominant ants were also not ed. Crematogaster species that build large carton nests, the most frequent species at canopy level (89.2% of the trees), represent here only 1.6% of t he ants; while groundnesting, arboreal-foraging species (i.e., Cr. striatul a and Ph, megacephala), the most frequent along the forest edges, were abse nt in the canopy. T. aculeatum, noted once on a vine in the canopy, was fre quent along the forest edge. Nevertheless, O. longinoda and C. brutus were noted in both microhabitats, but were more frequent along the forest edge.