Abstract: Environmental changes, especially climate variability, can substantially influence phenological patterns of plants and their associated insect communities, potentially reshaping the spatial distribution of their interactions. Despite considerable attention on species range shifts under climate change, empirical studies explicitly addressing how these shifts affect spatial matching between plants and their associated insect communities remain scarce. Here, we investigated inter-annual changes in the spatial matching between the poisonous weed Stellera chamaejasme L. and its associated floral visitor community along an altitudinal gradient over two climatically distinct growing seasons in the Qilian Mountains, China. We monitored the flowering phenology of S. chamaejasme and the abundance of its major pollinators (Meloidae, Tachinidae, Scarabaeidae and Noctuidae) at different altitudes. Our findings show a pronounced altitudinal displacement between the peak abundance zones of S. chamaejasme and its major pollinators, indicating spatial mismatches in both years (2021 and 2022). However, the increased preseason thermal accumulation in 2022 improved spatial matching, as high-density overlap zones shifted to higher altitudes, where insect visitation rates also increased. Additionally, the elevated preseason heat significantly advanced flowering phenology at high altitudes, which may contribute positively to breaking the altitudinal distribution limits of S. chamaejasme, along with enhanced spatial matching with pollinators. This study highlights the significant impact of inter-annual climate variability on spatial matching between mountain plants and pollinators at various altitudes, which is crucial for improving population dynamics models and enhancing the accuracy of predictions.

Key words: flowering phenology, spatial matching, inter-annual climate variability, altitudinal distribution