Minimal Spillover of Native Small Mammals From Bornean Tropical Forests Into Adjacent Oil Palm Plantations

Philip M Chapman,Robin Loveridge,Charles W Davison,Chris Carbone,Robert M Ewers,J Marcus Rowcliffe,Henry Bernard

doi:10.3389/ffgc.2019.00002

Abstract

In the face of rapid tropical agricultural expansion, preservation of tropical forest remnants is crucially important. Forest remnants often abut the edges of new or established plantations, so landscape-level conservation requires an understanding of the balance between ecosystem services and disservices provided by forest, including potential crop yield reductions caused by species such as rodents, an important pest group in oil palm plantations. However, very little is known about the scale of any spillover of native species which inhabit forest into adjacent agricultural areas. We examined the distribution and behaviour of small mammals across an edge separating logged tropical forest and oil palm plantations in Sabah, Malaysian Borneo, using a dual approach. We used a trapping grid to reveal patterns of species relative abundance across the forest-plantation edge, and tracked individuals of forest species using a spool-and-line. We uncovered little evidence that the native forest small mammal community crosses the edge and uses the plantation, although two invasive small mammal species were found across the whole edge gradient. Of 10 forest species detected, we found only the adaptable murid Maxomys whiteheadi in the plantation, where it persisted at low abundances across all sampling points, including in the plantation interior control site. This pattern is more consistent with persistence of M. whiteheadi throughout plantations than with spill-over from forest fragments. On the forest side, observed species richness of small mammals increased with distance into the interior, suggesting a negative edge effect may exist within forest remnants. Of 23 successfully tracked small mammals, only one M. whiteheadi crossed the forest-plantation edge, and overall, this species was significantly repelled from crossing into plantation habitat. Our results suggest that spillover of native small mammals contributes little to oil palm damage close to forest-plantation edges, but that oil palm negatively impacts small mammal populations within adjacent forest remnants.

Highlights

Of the remaining nine native species captured in forest, four were captured immediately at the forest-plantation edge (0 m), a further three were only captured 23 m into the forest and two species were only captured at 46 m into the forest (Table 1)
Our results reveal little evidence that native small mammal communities spill over from forest into adjacent oil palm plantations, and we reject our hypotheses that the majority of native small mammals use the plantation with elevated abundance near the edge, but declining abundance with increasing distance into the plantation
We focussed on the distribution and movement of native small mammal species at the forest-plantation edge, we found no evidence that forest harbours elevated abundance of the invasive R. exulans and R. rattus

Summary

Introduction

Maximising the remaining area of tropical forest amid agricultural expansion is a priority for conservation (Gibson et al, 2011; Wilcove et al, 2013), especially in Southeast Asia where the expansion of oil palm (Elaeis guineensis) continues to threaten one of the world’s great biodiversity hotspots (Fitzherbert et al, 2008; Wilcove et al, 2013; Yue et al, 2015; Vijay et al, 2016). Spillover may involve transient dispersal and foraging movements in either direction across the habitat boundary, and may involve species providing ecosystem services such as pest control (Koh, 2008; Lucey et al, 2014; Nurdiansyah et al, 2016); or ecosystem disservices such as crop damage, which harms yields and profits (Zhang et al, 2007). Even if there is a net positive effect of retaining forest remnants in plantations, if stakeholders regard them as pest reservoirs they are likely to resist efforts to conserve those remnants, contributing to local and global losses of biodiversity from tropical deforestation (Bradshaw et al, 2009; Wilcove et al, 2013)

Methods

Results

Discussion

Conclusion