Differences in Nectar Traits between Ornithophilous and Entomophilous Plants on Mount Cameroon

Abstract

Despite a growing number of studies, the role of pollinators as a selection agent for nectar traits remains unclear. Moreover, the lack of data from some biogeographic regions prohibits us from determining their general importance and global patterns. We analyzed nectar carbohydrate traits and determined the main pollinators of 66 plant species in the tropical forests of Mount Cameroon (tropical West Africa). The measured nectar traits included total sugar amounts and proportions of sucrose and hexoses (i.e., glucose and fructose). We report the nectar properties for plants visited by five pollinator groups (bees, butterflies, moths, hoverflies, and specialized birds). Our results indicate that, rather than specific evolution in each of the five plant groups, there was a unique nectar-trait evolution in plants pollinated by specialized birds. The ornithophilous plants had a higher proportion of sucrose and produced larger sugar amounts than the plants pollinated by insects. We also demonstrated a significant phylogenetic signal in the nectar properties in some lineages of the studied plants.

Spatiotemporal variation in the role of floral traits in shaping tropical plant‐pollinator interactions

“…T A B L E 1 Floral traits' importance (expressed as the Mean Decrease in Accuracy), sensitivity and specificity for individual primary pollinator groups and for the whole RF models with the three most important traits plants during the wet season (Janeček et al, 2015) whilst being more generalised during the dry season (Janeček, Chmel, Ewome, et al, 2021). Additionally, the seemingly low predictability of our models for some primary pollinators could also be related to the complexity of plantpollinator interactions, whilst our analyses focused on a few selected floral traits.…”

“…This was converted to the amount of sugar per flower by multiplying it with the measured volume in capillary tubes. For low‐nectar producing flowers, we washed the flowers using a Hamilton syringe with filtered water, added ethanol to the samples and boiled it for 15 min to deactivate enzymes (Chlumská et al, 2014; Janeček, Chmel, Ewome, et al, 2021). The nectar samples were dried in the laboratory, where they were transferred into constant volumes.…”

Cheaters among pollinators: Floral traits drive spatiotemporal variation in nectar robbing and thieving in Afrotropical rainforests

“…We measured ten floral traits (Table S2; partly used in Klomberg et al ., 2022). Three of these were morphometric (corolla size, and the length and width of nectar tube), and seven were qualitative characterising floral shape (bell, bowl, dish, funnel, gullet, labiate, open, papilionaceous, salverform, stellate, trumpet, tube, urceolate), symmetry (zygo- and actinomorphy), orientation (horizontal, pendant, upright), colour (brown, green, orange, pink, purple, red, white, yellow), nectar guides (presence/absence), brightness (vivid/drab), and odour strength (none, weak, strong), and amount of nectar sugar (measured as 24-hour production in flowers in-situ, as described in (Janeček et al ., 2021).…”

“…In our study, nectar robbing was more frequent in the wet season, where flowers with longer nectar tubes and generally narrower corollas were more common (Fig 2A). Such flowers were prevalent in the wet season, where their morphology could help avoid nectar dilution (Aizen, 2003) or specialise to their pollinators with higher energetic needs (Chmel et al, 2021). However, such specialised flowers are more often robbed by small-tongued visitors unable to reach their nectar through the flower opening (Bronstein, 2001;Navarro & Medel, 2009;Maruyama et al, 2015).…”

“…Floral traits can also vary seasonally, as some plants blooming in rainy seasons have closed flowers with narrow tubes (Klomberg et al ., 2022) that prevent nectar dilution (Aizen, 2003) and washing away of pollen (Mao & Huang, 2009). In the tropics, ornithophilous plants are commoner in the wet season, as seen with sunbird-pollinated plants on Mount Cameroon (Janeček et al ., 2021).…”