Biodiversity patterns are the sum of multiple overlapping species distributions. Their analysis therefore requires proper species inference. DNA-based species delimitation has become increasingly popular for such assessments and their robustness is often measured by congruence of multiple delimitation approaches. We explore how contrasting results of different species delimitations translate into conclusions of synecological studies, exemplified by assemblages of phytophagous scarab beetles in Sri Lanka from different elevations and forest types. Particularly, we compared estimates based on complete assemblages and on cumulated species inventories inferred from individually analysed subclades. These patterns of assemblage similarity were analysed across different spatial scales with reference to morphospecies and haplotypes. Method-related ambiguity of species estimates, which also included subclade inferences, affected severely the certainty of apparent biodiversity patterns at most spatial scales. In this case study of tropical beetle, haplotypes only provided very little explanatory information, since genetically highly diverse populations widely lacked shared haplotypes.