Intensive agroforestry practices negatively affect ant (Hymenoptera: Formicidae) diversity and composition

Abstract

Many natural forests in southeast Asia have been replaced by agroforestry systems with increasingly intensive management practices. To test the effects of intensive agroforestry practices on the retention of rainforest biodiversity, we quantified ant diversity and composition in three cocoa plantations versus three rainforest remnants in the remote Mekongga Mountains of southeast Sulawesi, Indonesia. Using three complementary sampling methods (pitfall trapping, leaf litter sifting, and baits) we found substantially more species, in total, at rainforest sites (67 spp.) than at the cocoa sites (43 spp.), and for all sampling methods there was significantly greater ant richness and diversity in rainforest habitats compared with cocoa plantations. Moreover, only 23 out of the total 87 species were shared between habitat types and an ANOSIM analysis showed that forest ant assemblages were significantly different from cocoa ant assemblages, with an average of 89.8% dissimilarity of species relative abundances between rainforest fragments and cocoa plantations. Whereas rainforest fragments were dominated by a diverse array of native species in the genera Pheidole, Prenolepis, Odontomachus and Tetramorium, cocoa plantations were dominated by the tramp ant species Anoplolepis gracilipes, Monomorium floricola and Nylanderia vaga. The results of this study suggest that intensive agroforestry can have a dramatic influence on ant species composition, promoting the establishment of invasive tramp ant species and the loss of rainforest specialist species. This contrasts with previous findings from lower intensity, shade grown cocoa, which suggest that agroforestry can be a ‘win-win’ for both biodiversity conservation and agricultural production. Our results suggest that intensive production practices have strong negative effects on native biodiversity in plantation agroforests, and effective conservation strategies should focus on limiting land use conversion to more intensive agroforestry systems.