Long-term Introduction of Western Honeybees Reorganizes Pollination Network in a Tibetan Alpine Meadow

The introduction of managed western honeybees (Apis mellifera) is often assumed to disrupt native ecosystems by competitively displacing local pollinators and altering plant communities. However, the simultaneous impacts on pollinator community composition, and plant-pollinator network properties remain poorly integrated. This study investigated these effects in a Tibetan alpine meadow with a long history of apiculture by comparing sites close to and distant from apiaries. Using field surveys and pollen transport network analysis, we demonstrate that while Apis mellifera significantly reduced the abundance of native bees, it concurrently increased the abundance of dipterans (specifically Tachinidae and Syrphidae). This shift is driven by a cascading effect: honeybees facilitate the proliferation of specific preferred host plants, creating a resource pulse that supports increased fly populations. Regarding network topology, honeybee introduction increased modularity and functional complementarity but did not alter network nestedness or robustness in general. These findings suggest that rather than simply simplifying the ecosystem, introduced honeybees reorganize the pollination network. Although the compensatory surge in fly populations maintains network structural robustness to some extent, the lower pollination efficiency of these opportunistic visitors compared to the displaced specialized native bees implies a potential functional degradation. This shift may fail to guarantee plant reproductive success, thereby posing a threat to the long-term persistence of the plant community.