The diversity and abundance of ants in relation to forest disturbance and plantation establishment in southern Cameroon.
Abstract
Tropical biodiversity is seriously threatened by deforestation but few studies have quantified its impact. We aimed to measure the impact of forest clearance and different methods of establishing Terminalia ivorensis (Combretaceae) forest plantations on the abundance, richness and composition of ants, the most abundant group of arthropods in tropical forest canopies, in the Mblamayo Forest Reserve in Cameroon. For canopy ants, we quantified the effects of different methods of plantation establishment by sampling two sets of plots subjected to complete clearance, partial mechanical clearance and partial manual clearance relative to uncleared forest reference plots. For leaf-litter ants, we quantified the impacts of different levels of forest disturbance along a gradient from near primary forest to complete forest clearance. A total of 97 ant species was recorded from the canopy (from approximately 48 500 individuals), at an average of 213 (±45) ants m-2. Jack-knife estimates of species richness showed that at one site, Bilik, 87% more species occurred in the partial manual clearance plot than the complete clearance plot, with the partial mechanical clearance plot intermediate. At the other site, Ebogo, ant richness did not vary between treatments. Ants were 20 times more abundant in the partial manual clearance plot in Ebogo than the partial manual clearance plot in Bilik, largely due to a numerous Technomyrmex species that might have reduced ant richness on this plot. Cluster analysis of the similarities in ant species composition between plots, calculated by the Morisita index, showed that site and treatment affected species composition. Neither treatment nor site affected the relative number of species in different nesting categories. A total of 111 ant species (from 3650 individuals) was recorded from the leaf litter, at an average of 52 (±4.6) ants m-2. Species numbers were greatest in the two partial clearance plots in Ebogo (52-53 species), lowest in the two complete clearance plots (37), and intermediate and most variable in the three uncleared forest plots (40-52). Cluster analysis showed that species composition was not affected by treatment, while neither treatment nor site affected the relative number of ant species in different feeding categories. Despite some local effects by dominant species, our results support the view that deforestation can reduce arthropod species richness. This study is unique in showing that reforestation methods (using a single tree species) can have a marked effect on arthropod species richness and composition. Specifically, it reveals that ant species richness can be greater in plantations established after partial manual clearance than complete clearance.