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.
Highlights
The vast majority of angiosperms rely on a diversity of animal pollinators to successfully complete reproduction (Ollerton et al 2011)
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 based on the number of deposited pollen grains in stigmas
Estimates of pollination effectiveness deriving from different functional groups, such as the ones described in this study, can contribute to a better understanding of communitylevel dynamics in tropical ecosystems
Summary
The vast majority of angiosperms rely on a diversity of animal pollinators to successfully complete reproduction (Ollerton et al 2011). The quantitative component usually measures the frequency of the interaction between a pollinator and a plant (e.g. visitation rates; Herrera 1987; Vázquez et al 2015; Schupp et al 2017), and the qualitative component measures the outcome of a pollinator visit (e.g. pollen deposition; Muchhala & Thomson 2010; Dellinger et al 2019, but see Herrera 1987, Schupp et al 2017 for other aspects of measuring quality). A pollinator that exhibits high visitation rates (quantitative component) may deposit a small number of pollen grains (qualitative component; Madjidian et al 2008). A pollinator may have low visitation rates but deposit a high number of pollen grains during each visit (Muchhala & Thomson 2010)
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