3.1 Spur length and flower visitor size
The average spur length of each population of A. buergeriana var.buergeriana varied in the range of 32.85–40.31 mm, confirming the presence of diversity in spur length within this species (Figure 1d; supplementary material, Figure S1, Table S2). No spatial autocorrelation of average spur length among populations was detected (Moran’s I statistic = –0.160, P = 0.757). PCA results for spur length, corolla diameter, and petal width roughly indicated a morphological separation among populations (supplementary material, Figure S2), but yellow- and red-flowered individuals could not be clearly separated on the basis of variations in flower morphology (supplementary material, Figure S2).
The average visitor size of each population varied in the range of 8.69–40.80 mm (bumblebees plus small bees) and 31.84–40.80 mm (only bumblebees) (supplementary material, Table S1). Five types of bumblebees were observed, in descending order of size: B. consobrinus queen,B. diversus queen, B. consobrinus worker, B. diversus worker, and B. honshuensis worker. Flower visits by small bees of the genus Ceratina were observed in several populations (supplementary material, Table S1). Average plant height of each population varied in the range of 54.84–98.01 cm.