Three-dimensional niche partitioning drives spider coexistence in alfalfa agroecosystems: enabling targeted biocontrol optimization.

BACKGROUND: Alfalfa (Medicago sativa), a globally vital forage crop, faces persistent pest pressures dominated by chemical control, with underexplored biocontrol potential. Here, we investigated arthropod dynamics in two alfalfa fields (2019-2021), testing the hypothesis that three-dimensional niche partitioning (temporal, spatial, and trophic) facilitates spider coexistence and may enhance biocontrol. RESULTS: Combining pitfall trapping (ground arthropods) and sweep netting (canopy arthropods) with molecular dietary profiling of five dominant spider species from three families (Lycosidae, Philodromidae, and Thomisidae), we demonstrated that spiders dominated the predator guild with significantly greater abundance and richness than other natural enemies. Temporal niche differentiation emerged through spiders' seasonally lagged responses to prey availability, featuring consistent bimodal activity peaks around May and August. Spatial niche segregation manifested as vertical stratification between ground and canopy microhabitats, reducing interspecific competition. Trophic niche complementarity occurred through species-specific prey specialization: ambush predators (Thomisidae) targeting late-season pests while cursorial hunters (e.g., Lycosidae) suppressed early season herbivores, thereby minimizing dietary resource overlap. Critically, staggered mowing maintained refuge habitats during key phenological windows, while structural habitat enhancement preserved vertical stratification, collectively optimizing spider-mediated biocontrol. CONCLUSIONS: Our findings indicate that the targeted management of spatiotemporal trophic niches by harnessing the innate biocontrol capacity of spiders may enable sustainable pest regulation, thereby reducing the reliance on agrochemicals in alfalfa agroecosystems. © 2026 Society of Chemical Industry.