Traditional land use associated with swidden agriculture changes encounter rates of the top predator, the army ant, in Southeast Asian tropical rain forests

Abstract

We examined the effect of traditional swidden agriculture on biodiversity using the litter arthropod top predator, the army ant Aenictus (Hymenoptera: Formicidae) as an indicator species in and around an intact tropical rain forest in Sarawak, Borneo, Malaysia. We compared the encounter rates with Aenictus colonies among five forest types: continuous primary forest, isolated primary forest, old secondary forest (>20 years elapsed after abandonment of the fields), young secondary forest (5 years after abandonment), and new fallow (2 years after abandonment) by intensive area searching in 2003 and 2005. In total, seven Aenictus species (15 colonies) and six Aenictus species (11 colonies) were encountered in 2003 and 2005, respectively. The encounter rates were the highest in continuous and isolated primary forests, intermediate in old and young secondary forests, and the lowest in new fallow. Year and the interaction between year and forest type were not significant. That is, abundance of top predators, which is rare and likely to be vulnerable to disturbance, has never fully recovered even 20 years after the termination of cultivation. We discuss forest management strategies to sustain biological diversity.