Abstract
Agricultural expansion across tropical regions is causing declines in biodiversity and altering ecological processes. However, in some tropical agricultural systems, conserving natural habitat can simultaneously protect threatened species and support important ecosystem services. Oil palm cultivation is expanding rapidly throughout the tropics but the extent to which non-crop habitat supports biodiversity and ecosystem services in these landscapes is poorly documented. We investigated whether riparian forest fragments (riparian reserves) provide a pest control service or increase pest activity (disservice) within oil palm dominated landscapes in Sabah, Malaysian Borneo. We assessed the activity of potential predators of pest herbivores using plasticine caterpillar mimics and quantified herbivory rates on oil palm fronds in areas with and without riparian reserves. We also manipulated the shape and colour of the mimics to assess the extent to which artificial pest mimics reflect a predatory response. The presence of riparian reserves increased the attack rate on mimics by arthropods, but not by birds. Our methodological study suggested attacks on artificial pest mimics provide a better indication of predatory activity for birds than for arthropod predators. Herbivory rates were also not significantly affected by the presence of a riparian reserve, but we found some evidence that herbivory rates may decrease as the size of riparian reserves increases. Overall, we conclude that riparian forest fragments of 30 – 50m width on each side of the river are unlikely to provide a pest control service. Nevertheless, our results provide evidence that these riparian buffer strips do not increase the density of defoliating pests, which should reassure managers concerned about possible negative consequences of preserving riparian buffers.
Highlights
Agricultural production relies on many ecosystem services; pollination, pest control and decomposition are among the most important
We retrieved 1547 plasticine mimics and 36 oil palms from which we measured the attack rate of potential predators of pests and corresponding herbivory rates. 474 caterpillars were attacked by arthropods, 322 by birds, and only 10 by mammals
We found some evidence that riparian reserves increase arthropod foraging activity in oil palm plantations, but in general this did not correspond to a change in herbivory on palm fronds
Summary
Agricultural production relies on many ecosystem services; pollination, pest control and decomposition are among the most important. In some agricultural systems this has caused an increase in production costs and a drop in yields (Power, 2010). It is increasingly important that we understand the biological systems underpinning key ecosystem services. The protection of natural habitat can increase densities of important service providers and enhance ecosystem services. Pollination and fruit set in coffee plantations increase with proximity to natural habitat (Klein, Steffan–Dewenter, & Tscharntke, 2003; Ricketts, 2004). Proximity to forest increases the densities of bird and bat species that feed on common pest species in coffee (Karp et al., 2013) and cacao plantations (Maas, Clough, & Tscharntke, 2013)
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