Ant mosaics in cocoa agroforestry systems of Southern Cameroon: influence of shade on the occurrence and spatial distribution of dominant ants

摘要

In African cocoa agroforestry systems, ants represent the most important part of arboreal arthropod biomass and play a crucial role in ecosystem functioning. The more abundant are supposed to be involved in crop pest regulation. However, the lack of knowledge about ecological interactions between ants and their habitat, including other ant species of the community, leaded to contradictory views on their efficiency as potential biological control agents. In the present study, we studied the impact of shade trees on the occurrence and spatial distribution of the most abundant ants of cocoa agroforestry systems of Southern Cameroon. We characterized shade of four traditional cocoa farms and described distribution patterns of numerically dominant ants through spatial analysis. Our results showed that the populations of the most abundant arboreal species, in our study Oecophylla longinoda, Tetramorium aculeatum, Crematogaster spp., Camponotus spp. were generally aggregated in plantations. However, the distribution structure of ant populations was variable between samples, suggesting that the normal development of ant colonies may interfere with ecological constraints like interspecific competition and abiotic factors. Distribution mapping as well as statistical analysis showed that highest densities of O. longinoda were sheltered by cocoa trees in the sunniest areas of plots. On the other hand, Crematogaster species were usually strongly aggregated in the most shaded areas. Mechanisms involved in ant/shade relationships were discussed and we suggested that a good management of shade may take into account ant communities, which could play a significant role in conservation biological control against cocoa pests.