Sunbirds serve as major pollinators for various populations of Firmiana kwangsiensis, a tree endemic to South China

Abstract

Loss of local, effective pollinators may potentially limit plant reproductive success but the plantpollinator interactions could be rescued if the plant does not reject other pollen vectors. Firmiana kwangsiensis H.H. Hsue (Malvaceae) is an endangered tree endemic to limestone areas in South China. Although its preservation status is listed as "critically endangered", its reproductive ecology is little known. We compared floral visitors in three wild populations and one transplanted population. Such a comparison allows us to see whether the pollinator assemblage varies geographically and to examine the plasticity of plant-pollinator interactions, informing sustainable ex situ conservation. Our pollination experiments indicated that fruit/seed set in F. kwangsiensis largely depended on pollinator visits, and was greatly reduced under hand self-pollination or exclusion of bird visits. Floral visitors included sunbirds, butterflies, and bees (honeybee and wasp) but their visitation frequency varied in the four populations. The sunbird Nectarinia jugularis was the major pollinator in the three wild populations, but was replaced by the other sunbird Aethopyga christinae in the ex situ population. This tree is showy, with orange-red flowers blooming before the leaves emerge. The calyx tube accumulates a large volume of dilute nectar (sugar concentration was 9.5%) in the morning, rewarding sunbird pollinators. Our investigations indicated that sunbirds rather than insects served as a functional group of pollinators for this endangered species. Successful ex situ conservation of this type of plant needs to consider the availability of potential pollinators.

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

“…To compare the effectiveness of insect and bird pollinators, we counted pollen grains deposited on the stigma of a virgin flower following a single visit by one of the pollinator species. To determine the importance of bird pollination to seed set, we compared seed set of open‐pollinated plants to caged plants that excluded birds but not bees (Huang et al, 2018). Inflorescences with flowers about to open were bagged with fine‐mesh nylon nets before flowering in late May 2018 in the high‐altitude population.…”

“…To further examine the role of sunbirds in pollination, 30 large cylindrical bird cages (30 × 60 cm) were fixed on the shrubs to exclude birds (Huang et al, 2018) at each site. Twenty cages on 10 different shrubs (each with two cages) were left in place until fruits developed 1.5 months later.…”

Plant-pollinator interactions in East Asia: a review

“…1H; Krauss et al 2017). Sunbirds act as pollinators of plants belonging to many families, such as Musaceae (e.g., Musa (Liu et al 2002)), Orchidaceae (e.g., Coelogyne )), Theaceae (e.g., Camellia (Qiu et al 2015;Sun et al 2017)), Ericaceae (e.g., Rhododendron (Huang et al 2017;Song et al 2019)), Hamamelidaceae (e.g., Rhodoleia (Gu et al 2010)), and Malvaceae (e.g., Firmiana (Huang et al 2018)).…”

Effective pollination of Aeschynanthus acuminatus (Gesneriaceae) by generalist passerines, in sunbird-absent East Asia

“…From the aspect of reward, flowers pollinated by birds usually secrete vast quantities of nectar in diluted concentrations 11,47 . Studies on the nectar properties of bird-pollinated species in East Asia were extremely limited until recently, when it was reported that several bird-pollinated species release large amounts of diluted nectar 17,22,48,49 . Our results regarding the large quantity (61 µL) and low sugar concentration (7%) of nectar produced by A. acuminatus support similar conclusions from these studies.…”