In Southeast Asia, biodiversity‐rich forests are being extensively logged and converted to oil palm monocultures. Although the impacts of these changes on biodiversity are largely well documented, we know addition to samples we collected in 201 little about how these large‐scale impacts affect freshwater trophic ecology. We used stable isotope analyses (SIA) to determine the impacts of land‐use changes on the relative contribution of allochthonous and autochthonous basal resources in 19 stream food webs. We also applied compound‐specific SIA and bulk‐SIA to determine the trophic position of fish apex predators and meso‐predators (invertivores and omnivores). There was no difference in the contribution of autochthonous resources in either consumer group (70–82%) among streams with different land‐use type. There was no change in trophic position for meso‐predators, but trophic position decreased significantly for apex predators in oil palm plantation streams compared to forest streams. This change in maximum food chain length was due to turnover in identity of the apex predator among land‐use types. Disruption of aquatic trophic ecology, through reduction in food chain length and shift in basal resources, may cause significant changes in biodiversity as well as ecosystem functions and services. Understanding this change can help develop more focused priorities for mediating the negative impacts of human activities on freshwater ecosystems.
We thank the Sabah Biodiversity Council, Yayasan Sabah, Danum Valley Conservation Area Management Committee and SEARRP for providing research permission (Licence No: JKM/MBS.1000‐2/2 JLD.3 (90)) for field work in Sabah. This study was supported by Sime Darby Foundation funding to the SAFE Project, RGS‐IBG grant (PRA 01/16) for electrofishing equipment, the Royal Society (grant NAF\R2\180791), AcRF Tier 1 grant from the Singapore Ministry of Education (National University of Singapore [NUS] grant number: R‐154‐000‐A32‐114) for sample analysis, the Landmark Trust Futures Scheme for a week long writing retreat where the project was conceptualized, and C. L. Wilkinson was supported by funding from the Faculty of Science, NUS, the Singapore Ministry of Education Research Scholarship Block (RSB) funding for Research Fellows and the Lee Kong Chian Natural History Museum. We also thank all field assistants at the SAFE project for help with fieldwork and lab members at Imperial College London, Queen Mary University of London and National University of Singapore for advice and guidance on design, analysis and helpful discussions. In addition, we thank the editor and reviewers for their valuable comments and suggestions, which improved the study. Author contributions: C. L. Wilkinson, J. H. Liew, K. W. J. Chua, D. C. J. Yeo, and P. Kratina conceived the ideas; C. L. Wilkinson, J. H. Liew, and K. W. J. Chua designed the methodology, C. L. Wilkinson collected the field data; R. Fiala and K. W. J. Chua prepared and analysed all samples; C. L. Wilkinson and K. W. J. Chua analysed the data; and C. L. Wilkinson led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication. The authors have no competing interests.