Ground-foraging ant communities vary with oil palm age

Abstract

The conversion of natural habitats to croplands is a major cause of the global loss of species diversity and ecosystem services. One potentially effective method for enhancing the biodiversity of important groups such as insects, and their associated ecosystem services within croplands, is to increase the environmental complexity of the agricultural matrix. This can be achieved in perennial tree crops by planting mixed-age stands. There is, however, very little evidence for the effects of stand age on biodiversity in tropical tree crops. In this study, we assess how ground-foraging ant communities differ in relation to oil palm stand age, currently the dominant tree crop across tropical Southeast Asia. Oil palm age did not affect overall ant species richness. However, the numbers of species that were either common or numerically-dominant decreased with increases in canopy cover, which positively correlated with oil palm age, suggesting greater species evenness in older oil palm. In mature, but not young, oil palm, ant species co-occurred non-randomly, suggesting competitive exclusion and species segregation. Species responses to variables associated with oil palm age depended on their functional group. Generally, opportunists and generalized myrmicines were less abundant and less diverse, whereas specialist predators were more abundant and diverse, in older oil palm. Our results show that ground-foraging ant communities in oil palm change significantly in composition, but not in species richness, with crop age. These results suggest that mixed-age stands could support compositionally variable communities and help boost insect diversity in otherwise homogeneous perennial monocultures.