Abstract

The world's forested landscapes are increasingly fragmented. The effects of fragmentation on community composition have received more attention than the effects on ecological processes, particularly in the tropics. The extent to which populations from forest fragments move (spillover) into surrounding agricultural areas is of particular interest. This process can retain connectivity between populations and alter the rate of beneficial or detrimental ecological functions. We tested whether riparian forest fragments (riparian reserves), are sources of two functionally important invertebrate groups (dung beetles and scavenging ants) within oil palm plantations in Malaysia. We also assessed whether forest fragments enhance rates of associated ecosystem functions (dung and bait removal). We found that oil palm sites with and without adjacent riparian reserves had similar overall beetle and ant communities and functional rates. However, dung beetle species richness, abundance and diversity declined with distance from a riparian reserve, providing evidence for a weak spillover effect. In addition, dung beetle community metrics within a riparian reserve predicted corresponding values in adjacent oil palm areas. These relationships did not hold for dung removal, ant community metrics or bait removal. Taken together, our results indicate that although riparian reserves are an important habitat in their own right, under the conditions in which we sampled they have a limited role as sources of functionally important invertebrates. Crucially, our results suggest that contiguous habitat corridors are important for maintaining connectivity of invertebrate populations, as forest dependent species may not easily be able to disperse through the agricultural matrix.

Highlights

  • Across the tropics, agricultural expansion and intensification are driving forest conversion and fragmentation (Gibbs et al, 2010)

  • Does biodiversity or ecosystem function differ between areas of oil palm with and without an adjacent riparian reserve?

  • The ant and dung beetle communities inside the riparian reserves were significantly different from those in oil palm adjacent to the riparian reserve, and those in oil palm sites without a riparian reserve

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Summary

Introduction

Agricultural expansion and intensification are driving forest conversion and fragmentation (Gibbs et al, 2010). Palm oil production is a major industry across the tropics, especially in Southeast Asia, and plantations are expanding in Africa and the Neotropics (Butler and Laurance, 2010; Wich et al, 2014). This expansion is of concern as the conversion of native habitats to oil palm causes declines in many taxa (Savilaakso et al, 2014) and ecosystem functions (Barnes et al, 2014b). The degree to which forest fragments act as sources for functionally important species in oil palm plantations is less well known

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