Pollinator effectiveness in the mixed-pollination system of a Neotropical Proteaceae, <i>Oreocallis grandiflora</i>

Abstract

In pollination systems with a diverse community of floral visitors, qualitative and quantitative variations in pollination effectiveness can lead to a system in which higher effectiveness results from the synergetic contribution of multiple pollinators. By employing a series of field and laboratory experiments in the south Andes of Ecuador, we compared the effectiveness of hummingbirds and nocturnal mammals visiting Oreocallis grandiflora, an Andean member of the Proteaceae. Pollinator effectiveness was measured with a quantitative component that assessed visitation rates to inflorescences and number of contacted stigmas per visit, and with a qualitative component that counted the number of deposited pollen grains in stigmas. Effectiveness estimates were complemented with controlled pollination experiments that contrasted fruit and viable seed set among flowers exposed to either diurnal or nocturnal pollination, self-pollinated flowers, and a control group with flowers exposed to naturally occurring pollination. Four species of hummingbirds and two species of nocturnal mammals visited the flowers of O. grandiflora. Hummingbirds outperformed nocturnal mammals in the quantitative components of pollination, while mammals were more effective than hummingbirds in the qualitative component. Pollination success was higher for the control group than for the other treatments, while hummingbirds and mammals performed similarly. Our findings suggest a case of functional complementarity in pollination: hummingbirds’ quantitative effectiveness complements nocturnal mammals’ qualitative effectiveness. Furthermore, our study demonstrates that pollination success in plants can be greater when flowers are visited by the whole diversity of pollinators.

Insect visitation and pollination of a culturally significant plant, Hopi tobacco (Nicotiana rustica)

“… 18 , 24 Small bees had the highest abundance based on their visitation rate, 32 and therefore may be the most effective visitors contributing to pollination. 33 Small bees were the most commonly documented visitor, making up 59% of all recorded interactions. Since visitation rates can serve as a measure of abundance, 32 we can conclude that small bees are the most abundant pollinators of N. rustica.…”

Bird and insect pollinators differ in specialization and potential pollination services along disturbance and resource gradients

“…Moreover, individual Cape sugarbirds showed high levels of flower constancy (Schmid et al, 2016) which should increase conspecific pollen transfer (Chittka et al, 1999). Although studies have shown that visitation frequencies and pollination quality may be unrelated in hummingbirds (Cárdenas-Calle et al, 2021;Watts et al, 2012), other studies from the Fynbos biome strongly suggest that birds are indeed reliable pollinators of proteas. The compact and protandrous protea florets mainly burst open by the strong force of probing bird pollinators (Collins & Rebelo, 1987), which explains why experimental studies found that birds are better pollinators than insects for many Protea species (Hargreaves et al, 2004;Schmid et al, 2015a).…”

Flower visitor networks: Reduced reproductive success driven by antagonists in a hummingbird‐pollinated species

“…Mutualist and antagonist floral effectiveness can thus be used as a proxy to estimate the variation in reproductive success among plants within populations depending on the quantity and the impact of visitations made by both pollinators and antagonists. Several studies have demonstrated that visitors with a high quantitative performance (e.g., insects) contrast with those of high qualitative performance (e.g., birds) in pollination effectiveness of plant species visited by multiple taxonomic and functional groups (Cárdenas‐Calle et al., 2020; Hervías‐Parejo & Traveset, 2018; Rodríguez‐Rodríguez et al., 2013). Therefore, determining the effectiveness of flower visitation among different types of flower visitors and individual plants is suitable to identify the most efficient pollinators against the most detrimental floral antagonists.…”