Studies have shown that food chain length is governed by interactions between species richness, ecosystem size and resource availability. While redundant trophic links may buffer impacts of species loss on food chain length, higher extinction risks associated with predators may result in bottom-heavy food webs with shorter food chains. The lack of consensus in earlier empirical studies relating species richness and food chain length reflects the need to account robustly for the factors described above. In response to this, we conducted an empirical study to elucidate impacts of land-use change on food chain length in tropical forest streams of Southeast Asia. Despite species losses associated with forest loss at our study areas, results from amino acid isotope analyses showed that food chain length was not linked to land use, ecosystem size or resource availability. Correspondingly, species losses did not have a significant effect on occurrence likelihoods of all trophic guilds except herbivores. Impacts of species losses were likely buffered by high levels of initial trophic redundancy, which declined with canopy cover. Declines in trophic redundancy were most drastic amongst invertivorous fishes. Declines in redundancy across trophic guilds were also more pronounced in wider and more resource-rich streams. While our study found limited evidence for immediate land-use impacts on stream food chains, the potential loss of trophic redundancy in the longer term implies increasing vulnerability of streams to future perturbations, as long as land conversion continues unabated.
Bibliographical noteFunding Information:
We gratefully acknowledge funding support from an AcRF Tier 1 grant from the Singapore Ministry of Education (National University of Singapore [NUS] grant number: R‐154‐000‐A32‐114), which supported J.H.L. and the work of K.W.J.C. K.W.J.C. was supported by the NUS President's Graduate Fellowship. C.L.W. was supported by funding from the Faculty of Science, NUS. Field research in Peninsular Malaysia was conducted with permission from the Economic Planning Unit in the Prime Minister's Department of Malaysia (permit number: UPE 40/200/19/3440). Field research in Sabah was conducted with permission from the Sabah Biodiversity Council, Yayasan Sabah, Danum Valley Conservation Area Management Committee and SEARPP (permit number: JKM/MBS.1000‐2/2 JLD.3(90)). We thank personnel from NUS, Universiti Malaysia Terengganu, and the Stability of Forest Ecosystems project for help with fieldwork; and Chris Yarnes from the University of California, Davis, for help with sample analysis.
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- compound-specific isotope analysis
- energy flow
- food chains
- food webs