Richness and Compositional Responses of Ants to Land use Change

Abstract

Human-made changes to the ecosystem are leading to the loss of biodiversity across the world. Western Ghats (WG) known for its rich biodiversity has historically undergone fragmentation and loss of its primary forest cover which has significant negative effects on biodiversity. Studies have shown that fragmentation almost invariably leads to a decrease in species richness, a pattern consistently observed across different taxonomic groups. Ants, one of the numerically dominant groups in forest ecosystems, play a vital role in many ecosystem processes and yet is one of the least studies groups within the WG landscape. The effect of land use change on ants in forests, fragments, native shaded coffee plantations and silver oak shaded coffee plantations was studied in the Kodagu district of Karnataka, India. We hypothesized that habitat heterogeneity would decrease from forests to fragments to native shaded coffee plantations and silver oak shaded coffee plantations and this would consequently lead to a decline in the richness and change in species composition of ants along this gradient. To test this prediction, ants were sampled along transects in the four-land use types using both pitfall traps and modified wrinkler extractors. As expected, there is a reduction in structural complexity across forest, fragments, native shade coffee and silver shade coffee plantations. We found that at the level of a transect, species richness reduced from forests to coffee plantations. Interestingly, the trend reversed when viewed at the scale of the land use, where all the forest sites together were the least species rich while the coffee plantations collectively showed the highest species richness. With respect to species composition, we found that coffee plantations had species adapted to drier environments whereas species inhabiting leaf litter were primarily found in forests and fragments. Coffee plantations with human residence inside had higher species compared to those not inhabiting. This study highlights the importance of scale for assessing the biodiversity potential of human modified habitats and for assessing their conservation potential.