Promiscuous pollinators—Evidence from an Afromontane sunbird–plant pollen transport network

Mlíkovský

et al. 2021

Preprint

Differences in bird-flower interaction specialization across continents serve as a common example of evolutionary trajectory specificity. While New World hummingbird-flower networks have been subject to numerous studies and are considered highly specialized, our knowledge of network specialization for their Old World counterparts, sunbirds (Nectariniidae), is completely insufficient. A few studies from tropical Africa indicate that sunbird-flower networks are rather generalized. Unfortunately, these studies are limited to dry seasons and high elevations around the tree-line, the environments where also niche-based hypotheses often predict lower resource partitioning. In our study, we explore the specialization of sunbird-flower networks and their spatio-temporal variability on Mt. Cameroon (Cameroon). Using a combination of automatic video recording and personal observations, we constructed eight comprehensive sunbird-flower networks in four forest types occurring in different elevations and in both the dry and wet season. As reported by previous studies the montane forest plants, birds and whole networks were highly generalized. Nevertheless, we observed much higher specialization in forests in lower elevations. The wet season was also characterised by higher, but not significant, specialization. While less specialized flowering trees dominated in dry season networks, more specialized herbs and shrubs were visited during the wet season. Whereas our findings do not support the generally accepted assumption that Old World bird-flower networks are rather generalized, we need further studies to understand the differences in bird-flower specialization on individual continents.

Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spatio-temporal Pattern of Specialization of Sunbird-flower Networks on Mt. Cameroon

Janeček

Mlíkovský

et al. 2021

Preprint

“…2k–l) birds that perched directly on the inflorescences will likely transfer pollen with their feet or other body parts as shown in a recent study of a montane system in Nigeria (Nsor et at. 2019).…”

Section: Discussionmentioning

confidence: 99%

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

Ewome²,

Gómez

et al. 2021

Oikos

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.

“…In addition, assimilation by specialized nectarivorous birds seemed to be similar for all three sugar types [40,45]. It is even more challenging to conclude why ornithophilous plants produce sucrose-dominant nectar when considering that field observation studies often report sunbirds feeding on a wide spectrum of plants other than ornithophilous plants [46][47][48].…”

Section: Differences In Nectar Properties In Relation To the Main Pollinatormentioning

confidence: 99%

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

Janeček

Ewome³

et al. 2021

Plants

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.