Temperature and a dominant dolichoderine ant species affect ant diversity in Indonesian cacao plantations

Agricultural land conversion and climate change play a major role in shaping tropical landscapes, but the direct and indirect links to biodiversity and species community composition remain little understood. We tested how landscape and environmental factors and management techniques, affect the diversity of ground and tree living ants in cacao plantations in Sulawesi (Indonesia). In addition, we investigated the occurrence of an aggressive, numerically dominant dolichoderine ant species (genus Philidris). Half of the 43 study plots, which differed in canopy cover, shade tree diversity, cacao tree age and their distance to the nearest rainforest, were weeded manually every 3 month, the others biannually. Each plot was divided into two subplots, one was fertilized twice a year whereas the other remained unfertilized. Using protein and sugar-solution baits, we examined species richness, abundances and interspecific interactions of ants on the ground and in cacao trees. In total we collected 160 ant morphospecies. Reduced ant species richness on the ground and in the trees was significantly correlated with higher mean temperatures while the other factors, including number of shade trees did not have any significant influence. The abundant and aggressive Philidris species, reduced arboreal ant species richness. It occurred more frequently in warmer, less shaded plots and on older cacao trees, which offer more nesting sites. In our study we show, that micro-climatic conditions and the occurrence of single ecologically dominant species are the major factors predicting species diversity in tropical agricultural ecosystems.