Floral structures affect on pollination events of sandalwood in four landraces along landscape gradients in Gunung Sewu, Java, Indonesia

Sandalwood, one of the most economic-endangered species, was the origin to the south-eastern islands of Indonesia, but is recently existed as new landraces in several community forests in Gunung Sewu Geopark, Indonesia. All of landraces consisted of three floral variants (YBF, refers to "yellow big flower"; RBF, "red big flower"; and RSF, "red small flower", respectively). Our previous findings reported differences on floral structures among variants. In this study we further analyzed these variants differences and its consequence on pollination events, among four landraces represented each geographical zone in Gunung Sewu Geopark, in the 2016 flowering periods. The flowering traits of each variant and landrace were measured. Floral visitors diversity, visitation rate and pollination behaviour were observed in each of population and floral variants. Results showed that flower abundance, visitor diversity and visitor abundance varied with sites but were similar among floral variants. Flowers abundance was strongly correlated to the pollinator visitation rate. Visitors diversity varied with sites due to the differences on flower abundance, environmental condition and altitude. The cooler and wetter site was visited more by Dipterans and Hymenopterans. The warmer, drier and lower sites were visited more by Lepidopterans and Dipterans. Sites with fewer flowers received less visitor diversity and abundance. Visitors preference to a given floral variant might be attributed to the differences on floral structures, sizes and colors. Lepidopterans belong to the moth groups (Arctiidae, Hesperiidae and Noctuiidae) preferred to visit the yellow flowers of YBF variant, while those belong to the butterflies groups (Papillionidae, Nymphalidae and Pieridae) preferred the red flowers of RBF and RSF. All six families of Hymenopterans preferred to visit the red flowers with bigger size, RBF. In contrast, all four families of Coleopterans, as well as the four families of Hemipterans, preferred the yellow flowers of YBF. All four families of Dipterans made similar visits to both RBF and YBF which have bigger flowers, while the visitation was less in RSF. © 2019 IOP Publishing Ltd. All rights reserved.