Altitude‐related shift of relative abundance from insect to sunbird pollination in Elaeagnus umbellata (Elaeagnaceae)

Abstract

The evolution of floral traits has been thought to be influenced by local, effective pollinators. However, little attention has been paid to the possibility that altitudinal variation in floral traits could be mediated by local pollinator functional groups, particularly a shift from bees to birds. Plant size, floral traits, pollinators and their pollination roles were investigated in the spring‐flowering shrub Elaeagnus umbellata (Elaeagnaceae) at three altitudes (1160, 1676, and 2050 m) in Minshan, Sichuan Province, on the northern rim of the Hengduan Mountains, southwest China. Compared to lower altitudes, higher‐altitude plants were smaller but the floral tubes were longer, with a larger volume of nectar of lower sugar concentration but with a greater proportion of sucrose. The visitation frequency of bees decreased with altitude, whereas the sunbirds did the opposite. Birds and bees foraged for nectar but not pollen, and birds deposited more pollen grains per visit relative to bees and least were syrphid flies. Excluding birds decreased seed set at high but not at mid‐ or low altitude. Our study of E. umbellata revealed an association between altitudinal variation in floral traits and a change in the relative abundance of the major pollinators with altitude from majority bees to majority sunbirds. Although abiotic factors also tend to vary with altitude and can affect floral traits, nectar properties of “pro‐bird” pollination were observed at high altitude.

Reproductive biology and pollinators of the invasive shrub Autumn olive (Elaeagnus umbellata Thunberg)

“…This study shows that these traits exist in E. umbellata but suggests that they are rare. However, it has been shown that reproductive strategies can vary greatly across a species' range and may be related to pollinator visitation (Toji & Itino, 2020; Pi et al, 2020). Therefore, it would be beneficial to examine whether these traits are more prevalent on the edge of the range in E. umbellata , where mates and pollinators are most likely to be limited (Levin, 2012).…”

Reproductive strategies of animal‐pollinated plants on high mountains: A review of studies from the “Third Pole”

“…Dipterans and Lepidopterans are the other two important pollinators. Interestingly, although rare, cases of bird pollination were observed in Leucosceptrum canum (Labiatae), whose flowers are open‐shaped with dark purple nectar (Zhang et al, 2012b), Caragana sinica (Pi et al, 2016), Elaeagnus umbellata (Elaeagnaceae, Pi et al, 2021), and large‐flowered Rhododendron species (Huang et al, 2017), and bat pollination in Oroxylum indicum (Bignoniaceae) in the foothills of the Western Himalaya was also observed (Vikas et al, 2009).…”

“…Later analysis of size variation in pollen aggregation by viscin threads across 13 Rhododendron species confirmed that pollen dispersal units varied with pollinator size (Song et al, 2019). A recent study observed an altitude‐related shift of relative abundance from insect to sunbird pollination in Elaeagnus umbellata (Elaeagnaceae) on the northern rim of the HMR (Pi et al, 2021), providing a first case of pollination ecotype in these mountainous areas. In other mountainous areas, for instance in the Southern Alps in France, along an elevation gradient from 970 to 2700 m, flies were the main potential pollinators above 1500 m; bee and beetle abundance decreased rapidly from this elevation (Lefebvre et al, 2018).…”

Altitudinal variation in phytochemical, physicochemical, and morphological aspects of Justicia adhatoda L. plant growing wildly in Western Himalayas

“…Similarly, in a study, noticeable variations in the morphological traits of Boswellia trees in Eritrea were observed. Tree height, crown diameter, and depth all decreased with increasing altitude [65,66]. The number of primary branches was found to be significantly low at 1330 masl, that is, 94.4 and high at 336 masl, that is, 139.8 and maximum number of secondary branches were found at 1330 masl, namely, 122.6.…”