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We investigated intra-reach-scale heterogeneity in autochthony of macroinvertebrate assemblages in a pristine montane stream in Borneo Island,Malaysia.Within a 300m at the altitude of 1600m,we set twelve sampling sites categorizing into four habitat types in relation to riffle-pool and canopy cover conditions;i.e.,open-pool,open-riffle,close-pool and close riffle.With three replicates of each habitat,we quantitatively sampled macro invertebrates and their potential food sources,and measured their carbon and nitrogen stable isotope ratios.We estimated reliance on autochthonous sources for each taxon using a two-source isotope mixing model.Most invertebrates depended both on autochthonous and allochthonous sources,while a few invertebrates mostly depended on autochthonous sources.For most of taxa there were no spatial variation in their isotopic signatures among the habitats,whereas some scrapers showed habitat-specificity reflecting isotopic variation in epilithon among habitats.We estimated the autochthony of macroinvertebrate assemblages for each habitat,summing up autochthonous biomass of each taxon.The autochthony of assemblage was significantly higher in riffles than in pools,and in riffle high canopy openness raised the autochthony of benthic assemblages.