Regional Differentiation of Ground–Active Beetle Assemblages Across Contrasting Dryland Alfalfa Agroecosystems

Perennial crops can provide a shared habitat template for arthropods, but whether regional differentiation persists among fields of the same crop in drylands remains unclear. From 2020 to 2022, we surveyed ground–active beetles at 55 perennial alfalfa sites across mountainous, oasis, and desert regions of Ningxia, China. We compared beetle diversity and feeding–guild structure among regions and examined their relationships with climate, soil, and vegetation. A total of 48,093 individuals representing 105 species, 62 genera, and 10 families were recorded. Agroecological region explained 30.1% of compositional variation and was associated with differences in total assemblages and all guilds. Mountainous sites had higher overall species richness and were dominated by detritivores; oasis sites contained a greater proportion of herbivores despite similar herbivore activity density among regions, whereas desert sites were numerically dominated by carabids and predators but had lower richness and diversity within the predatory guild. Regional differentiation was more evident in richness, assemblage composition, and trophic organization than in Shannon and Simpson diversity. β–diversity was dominated by nestedness. Climate was associated mainly with activity density and alpha diversity, whereas vegetation showed more recurrent associations with beta diversity. Ground–active beetle assemblages therefore remained regionally distinct despite occurring in the same perennial crop, supporting biodiversity assessment that accounts for dryland regional context.