Bird pollination syndrome is the plant's adaptation to ornithophily, but nectarivorous birds are not so selective

Abstract

Many tropical plants are pollinated by birds and several bird phylogenetical lineages have specialised to a nectar diet. The long‐assumed, intimate ecological and evolutionary relationship between ornithophilous plants and phenotypically specialised nectarivorous birds has nevertheless been questioned in recent decades, where such plant–pollinator interactions have been shown to be highly generalised. In our study, we analysed two extensive interaction datasets: bird–flower and insect–flower interactions, both collected on Mt Cameroon, west‐central Africa. We tested if: 1) insects and birds interact with distinct groups of plants; 2) plants with a typical set of ornithophilous floral traits (i.e. bird pollination syndrome) interact mainly with birds; 3) birds favour plants with bird pollination syndrome and; 4) if and how the individual floral traits and plant level nectar production predict bird visitation. Bird‐visited plants were typically also visited by insects, while approximately half of the plants were visited by insects only. We confirmed the validity of the bird pollination syndrome hypothesis, as plants with bird‐pollination syndrome traits were visited by birds at a higher rate and mostly hosted a lower frequency of visiting insects. However, these ornithophilous plants were not more attractive than the other plants for nectar‐feeding birds. Nectar production per plant individual was a better predictor of bird visitation than any other floral trait traditionally related to the bird pollination syndrome. Our study thus demonstrated the highly asymmetrical relationship between ornithophilous plants and nectarivorous birds.

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

“…Additionally, the seemingly low predictability of our models for some primary pollinators could also be related to the complexity of plant‐pollinator interactions, whilst our analyses focused on a few selected floral traits. For instance the low ability of complex models to predict plants visited (or unvisited) by birds is congruent with a recent study on the asymmetric nature of sunbird‐plant interactions (Chmel et al, 2021). Its authors demonstrated that while few plants with bird‐pollination syndromes were frequently visited by birds, they also visited a wide spectrum of plants with other traits.…”

“…According to the individual RF analyses (Table 3), nectar sugar production was indeed more important for bird pollination. It has been already suggested that mainly food rewards determine pollinators’ floral choice (Chmel et al, 2021; Janeček, Chmel, Ewome, et al, 2021; Schmid et al, 2016; Waser et al, 2018). Additionally, red and orange flower colours, associated with the bird pollination syndrome (Faegri & van der Pijl, 1979) and proven by numerous studies (Rodríguez‐Gironés & Santamaría, 2004; Wester et al, 2020, although see Waser et al, 2018), were confirmed important to determine the composition of the pollinators (Figure 2b).…”

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

“…Sunbirds were the second most frequent robbers in our study, in concordance with other studies (Geerts & Pauw, 2009). Although flowers can often be adapted to ornithophily, sunbirds are attracted to flowers with a high amount of nectar, regardless of other floral traits ((Chmel et al ., 2021b). Thus, when their bills are too short to access nectar within long-spurred flowers, they often resort to nectar robbing (Janeček et al ., 2015).…”

The habitat suitability of Timor friarbird (Philemon inornatus) in Western Timor Island, Indonesia

“…This is in line with Scoble and Clarke (2006), that nectarivorous birds (family Meliphagidae) prefer flowers that contain large amounts of nectar. It is a better predictor of bird visitation (Chmel et al 2021).…”