Key drivers of flowering phenology of alpine-plant communities: exploring the contributions of climatic restriction and flower-visitor composition across geographic regions

Abstract

Abstract Flowering phenology of alpine-plant communities is determined by the interaction between abiotic and biological factors. Bees (especially bumble bees) and flies are major pollinators in alpine ecosystems. The abundance of bumble bees consistently increases with seasonal progress reflecting the colony development cycle, while the abundance of flies often fluctuates unpredictably. Responding to the seasonal dynamics of pollinators, flowering phenology of alpine-plant communities may also vary between bee-visited and fly-visited plants within and among regions. We compared the relationship between flower-visitor composition and flowering phenology across geographic regions: fly-dominated alpine in New Zealand, subtropical alpine in Taiwan, mid-latitudinal alpine in central and northern Japan, and high-elevation grassland in Mongolia. Thermal gradient was a fundamental factor regulating flowering patterns across regions, and clear seasonality at higher latitudes created diverse flowering patterns at a community scale. Flower production of fly-visited plants was less predictable with large variation, whereas that of bee-visited plants showed consistent patterns across regions reflecting the seasonality of bees. In New Zealand, most plant species were linked to syrphid and/or non-syrphid flies, but the network structure between insects and plants varied between sites. The network structures of the East Asian alpines were commonly constituted by syrphid flies, non-syrphid flies, and bumble bees, and these groups had specific niche width. In the Mongolian grassland, many insect groups formed diverse networks with small niche overlap. These results suggest that the flowering phenology of alpine-plant communities is influenced by the seasonal activity of bee pollinators under the climatic restriction in each region.