Abstract
Understanding the interaction between reward-seeking flower feeding animals and plants requires consideration of the dynamic nature of nectar secretion. Studies on several plants suggest that nectar secretion may increase in response to its removal, but it is not clear whether the phenomenon is widespread. We determined whether 11 species of Colorado mountain wildflowers showed removal-enhanced nectar replenishment (RENR). We measured floral phenology, nectar volumes, rate of replenishment, and compared the cumulative nectar produced following five hourly removals with that accumulated after five hours. Nectar replenishment occurred rapidly, within minutes; statistically significant RENR was observed in 9 of our 11 study species, with the strongest effects in bee-pollinated species. We discuss the implications of RENR in plant species on the measurement of nectar, the adaptive advantage of RENR, and the energetic costs of RENR.
Highlights
The study of nectar secretion schedules is central to pollination ecology
Calculating the energetic return that a forager can expect while nectar-feeding at a particular flower species is complicated by the variable and dynamic nature of nectar secretion
Mean anthesis duration varied from 2.4 days in Mertensia fusiformis to 9.5 days in Delphinium nuttallianum, and in seven species the flowers were protandrous while the remaining four species had hermaphroditic flowers with no dichogamy (Tab. 1)
Summary
The study of nectar secretion schedules is central to pollination ecology. From a plant’s viewpoint, flower nectar schedules have the potential to influence the type, schedule, and behaviour of pollinator visits, affecting pollen transfer and fitness. From a flower-feeding animal’s viewpoint, flower nectar schedules have the potential to influence foraging strategies in time and space, and energetic returns and fitness. For the study of plant-pollinator energetics in particular, some early treatments extolled the relative simplicity of measuring floral nectar and its sugar content. By extracting a flower’s nectar with a capillary tube at one time point and estimating its sugar content by refractometry, one can establish both volume and approximate energy value in less than a minute. This is considerably easier than determining the dietary value of a leaf or a seed. Flowers can dynamically control nectar production: both volume and sugar content
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