Landscape Structure of Flowering Phenology in Alpine Ecosystems: Significance of Plant–Pollinator Interactions and Evolutionary Aspects

Abstract

Spatiotemporal variation in flowering phenology at community scale is an important structure in alpine ecosystems. The composition of flowering species at a regional scale changes drastically on a weekly scale during the short summer. In early snowmelt year, flowering more often overlapped among species, and the whole flowering period was shorter than in usual year. The major pollinators in Japanese alpine ecosystems are flies and bees. Approximately 50 % and 30 % of insect-pollinated plant species were predominantly visited by flies and bees, respec- tively. Bee-pollinated flowers showed a dispersed flowering pattern in which anthesis of early bloomers corresponded with the active period of queen bumble- bees, while that of late bloomers with the active period of worker bumblebees. Fly-pollinated flowers showed a peak in their flowering in the middle of the season when the ambient temperature was high. In an extremely warm summer, the flowering season finished earlier, and the synchrony of flowers and pollinators was disrupted because the life cycle of bees did not keep pace with the rapid progression of the flowering season. This phenological mismatch suggested a fragile relationship between plants and bees. Phenological isolation of pollen- mediated gene flow between local plant populations caused a spatial genetic structure within a local area. The restriction of gene flow could accelerate local adaptation. Because pollinator activity often increased as the season progressed, both fruit-set success and outcrossing rate increased in populations in late- snowmelt habitats. Such variations in reproductive success may cause life history variation at the local scale.