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

Abstract

The pollination syndrome hypothesis predicts that plants pollinated by the same pollinator group bear convergent combinations of specific floral functional traits. Nevertheless, some studies have shown that these combinations predict pollinators with relatively low accuracy. This discrepancy may be caused by changes in the importance of specific floral traits for different pollinator groups and under different environmental conditions. To explore this, we studied pollination systems and floral traits along an elevational gradient on Mount Cameroon during wet and dry seasons. Using Random Forest (Machine Learning) models, allowing the ranking of traits by their relative importance, we demonstrated that some floral traits are more important than others for pollinators. However, the distribution and importance of traits vary under different environmental conditions. Our results imply the need to improve our trait‐based understanding of plant‐pollinator interactions to better inform the debate surrounding the pollination syndrome hypothesis.

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

“…), and montane (2,200 m a.s.l. ), once each in the wet and dry seasons (for details, see Table S1, and Klomberg et al ., 2022). At each elevation, we established six transects (200 × 10 m) spaced at least 100 m apart to represent the local vegetation heterogeneity.…”

“…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).…”

“…Mainly, the spatiotemporal variation of nectar robbing and thieving has not been quantified at the community level, although it can be expected to follow spatiotemporal changes in floral traits of plant communities (Irwin & Maloof, 2002). For instance, the community composition of floral traits varies along elevational gradients (Albrecht et al ., 2018; Klomberg et al ., 2022). At higher elevations, lower temperatures raise the energetic requirements of pollinators (Classen et al ., 2015).…”

“…At higher elevations, lower temperatures raise the energetic requirements of pollinators (Classen et al ., 2015). This may increase the importance of traits related to nectar production and composition for floral visitors (Klomberg et al ., 2022). 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).…”

“…This may increase the importance of traits related to nectar production and composition for floral visitors (Klomberg et al ., 2022). 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).…”