Fine‐scale dietary differentiation among sympatric phytophagous scarab beetles

Understanding how ecologically similar species coexist remains a central challenge in ecology, particularly in polyphagous assemblages where dietary overlap limits differentiation along a single niche axis. Although coexistence theory emphasizes multidimensional niche partitioning, empirical studies integrating spatial, temporal and dietary dimensions remain scarce. In this study, multidimensional niche partitioning was examined in a community of phytophagous scarab beetles across agricultural fields, forests and grasslands in northeastern China. Habitat‐level surveys, fine‐scale temporal monitoring, olfactory preference assays and DNA metabarcoding of larval gut contents were combined to quantify niche differentiation across spatial, temporal and dietary dimensions. Species exhibited strong habitat segregation at landscape scale, consistent with habitat filtering as a primary structuring process. Within agricultural habitats where multiple species co‐occurred, temporal differentiation reduced but did not eliminate overlap. Gut content composition differed significantly among species, although mean dietary overlap did not differ from null expectation. Patterns of olfactory preference closely corresponded to realized diet composition: species with strong olfactory preferences maintained narrower realized diets, whereas species without strong olfactory preferences exhibited broader and more variable resource use. These results suggest that fine‐scale differences in resource use may contribute to niche differentiation among sympatric phytophagous beetles, even when overall dietary overlap remains high. By linking olfactory preference to realized dietary composition, this study highlights how behavioural traits can help explain subtle but consistent differentiation in host use among co‐occurring belowground herbivores.