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Summary Floral colour mediates plant–pollinator interactions by often signalling floral resources. In this sense, hummingbird‐pollinated flowers are frequently red‐coloured, and there are two tentative hypotheses to explain this pattern: 1. hummingbirds are attracted to red due its easier detection and 2. bees are sensorially excluded from red flowers. The second hypothesis is based on bees’ red colour blindness, which lead them to be less frequent and less important than hummingbirds as pollinators of red‐reflecting flowers. Here, we untangled the role of different flower traits mediating plant–pollinator interactions and empirically tested the above hypotheses. We chose Costus arabicus due to its synchronopatric white‐ and pink‐flowered individuals and its bee and hummingbird pollination system. Although pink flowers are not totally achromatic as pure red ones, they show an achromaticity degree that could drive bee exclusion. Specifically, we tested whether differences on red reflectance work attracting hummingbirds or excluding bees and the consequent implications for the plant's reproduction. Flower colour morphs of C. arabicus do differ neither in morphology nor in nectar sugar content. Moreover, white and pink flowers can be discriminated by the bees’ and hummingbirds’ colour vision system. Both groups are able to discriminate the red colour variation morph on the flower petals, the white flowers being more easily detected by bees and the pink flowers by hummingbirds. Bees preferentially visited the white flowers, whereas hummingbirds visited both colours at the same rate – both patterns corroborating the second hypothesis. Pollen loads deposited on stigmas did not differ between flower colour morphs, indicating that bees and hummingbirds play a similar role in the overall pollen deposition. However, bees are more likely to self‐pollinate than hummingbirds. Self‐pollination limits C. arabicus reproduction, and red‐reflecting flowers may be better pollinated by discouraging bee visitation. Therefore, the intraspecific colour variation is driving flowers to show colour‐related different levels of generalization. Our results support the ‘bee avoidance’ rather than the ‘hummingbird preference’ hypothesis. Sensory exclusion of bees seems to be the pressure for red‐reflecting flowers evolution, driving specialization in hummingbird‐pollinated flowers due to the costs of bee pollination on plant reproduction.

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Within Apocynaceae, interactions with pollinators are highly structured both phylogenetically and biogeographically. Variation in transition rates between pollination systems suggest constraints on their evolution, whereas regional differences point to environmental effects such as filtering of certain pollinators from habitats. This is the most extensive analysis of its type so far attempted and gives important insights into the diversity and evolution of pollination systems in large clades.

“Pollination syndromes” are specific combinations of floral traits that are proposed to evolve convergently across angiosperm lineages in response to different types of animal pollinators. In spite of their long history, pollination syndromes have not been tested adequately–they rarely have been examined critically to determine how well they describe floral trait diversity or predict pollinators. In a recent meta-analysis of data from the literature, Rosas-Guerrero et al. (2014) provide a welcome test that draws on insights from past studies. At the same time, their study illustrates several difficulties of meta-analysis approaches in general, and for pollination biology in particular. Here we discuss those difficulties and propose some solutions. We first consider how to gather studies from the literature without introducing unintended bias, such as the old-fashioned method of working backward from cited literature. We next consider how to deal with difficulties that invariably arise when extracting and analyzing often-incomplete information from heterogeneous studies. Finally we discuss issues of interpreting and presenting the results in the most informative manner. We conclude that although Rosas-Guerrero et al. (2014) and other studies such as Ollerton et al. (2009) have arrived at different conclusions about the utility of pollination syndromes, their results are not necessarily incompatible.

Functional traits can determine pairwise species interactions, such as those between plants and pollinators. However, the effects of biogeography and evolutionary history on trait‐matching and trait‐mediated resource specialization remain poorly understood. We compiled a database of 93 mutualistic hummingbird–plant networks (including 181 hummingbird and 1,256 plant species), complemented by morphological measures of hummingbird bill and floral corolla length. We divided the hummingbirds into their principal clades and used knowledge on hummingbird biogeography to divide the networks into four biogeographical regions: Lowland South America, Andes, North & Central America, and the Caribbean islands. We then tested: (a) whether hummingbird clades and biogeographical regions differ in hummingbird bill length, corolla length of visited flowers and resource specialization, and (b) whether hummingbirds' bill length correlates with the corolla length of their food plants and with their level of resource specialization. Hummingbird clades dominated by long‐billed species generally visited longer flowers and were the most exclusive in their resource use. Bill and corolla length and the degree of resource specialization were similar across mainland regions, but the Caribbean islands had shorter flowers and hummingbirds with more generalized interaction niches. Bill and corolla length correlated in all regions and most clades, that is, trait‐matching was a recurrent phenomenon in hummingbird–plant associations. In contrast, bill length did not generally mediate resource specialization, as bill length was only weakly correlated with resource specialization within one hummingbird clade (Brilliants) and in the regions of Lowland South America and the Andes in which plants and hummingbirds have a long co‐evolutionary history. Supplementary analyses including bill curvature confirmed that bill morphology (length and curvature) does not in general predict resource specialization. These results demonstrate how biogeographical and evolutionary histories can modulate the effects of functional traits on species interactions, and that traits better predict functional groups of interaction partners (i.e. trait‐matching) than resource specialization. These findings reveal that functional traits have great potential, but also key limitations, as a tool for developing more mechanistic approaches in community ecology. A free Plain Language Summary can be found within the Supporting Information of this article.

Contextualização do Relatório Temático sobre polinização, polinizadores e produção de alimentos no Brasil no escopo da Plataforma Brasileira de Biodiversidade e Serviços Ecossistêmicos (BPBES) 1.1. Marco conceitual da Plataforma Brasileira de Biodiversidade e Serviços Ecossistêmicos (BPBES) 1.2. Arcabouço geral sobre polinização, polinizadores e produção de alimentos 1.3. Polinização como serviço ecossistêmico 1.4. Público-alvo 1.5. Objetivos 1.6. Metodologia da revisão sistemática da literatura 2. O status e as tendências em polinização e produção de alimentos no Brasil 2.1. Conhecimento sobre polinização e polinizadores de plantas relacionadas à produção de alimentos 2.2. Principais grupos de polinizadores e sistemas de polinização 2.3. Dependência e valoração do serviço ecossistêmico de polinização 2.4. Déficit na polinização e ganhos com manejo de polinizadores: custos sociais, econômicos e ambientais da polinização suplementar 3. Diversidade biocultural e valores socioculturais dos polinizadores 3.1. Usos culturais e conhecimentos tradicionais sobre polinizadores 3.2. Manejo de polinizadores com ênfase na produção de mel e valores bioculturais associados 4. Fatores que afetam os polinizadores, a polinização e a produção de alimentos 4.1. Requerimentos ambientais de polinizadores 4.1.1. Recursos alimentares 4.1.2. Outros requerimentos ambientais 4.2. Ameaças aos polinizadores, à polinização e à produção de alimentos 4.2.1. Ameaças ambientais 4.2.2. Ameaças biológicas 4.3. Impacto de mudanças ambientais na diversidade e funcionalidade de polinizadores 4.3.1. Alterações no uso da terra 4.3.2. Mudanças climáticas 4.3.3. Espécies exóticas 5. Respostas aos riscos, governança e oportunidades associados aos polinizadores, à polinização e à produção de alimentos 6. Referências bibliográficas Anexo I. Revisão sistemática da literatura sobre polinização, polinizadores e produção de alimentos no Brasil Anexo II. Referências bibliográficas resultantes da revisão sistemática da literatura Anexo III. Plantas cultivadas e silvestres utilizadas direta ou indiretamente na produção de alimentos no Brasil, a dependência da polinização e seus visitantes florais e polinizadores

The tropical Melastomataceae are characterized by poricidal anthers which constitute a floral filter selecting for buzz‐pollinating bees. Stamens are often dimorphic, sometimes with discernible feeding and pollinating functions. Rhynchanthera grandiflora produces nectarless flowers with four short stamens and one long stamen; all anthers feature a narrow elongation with an upwards facing pore. We tested pollen transfer by diverse foraging bees and viability of pollen from both stamen types. The impact of anther morphology on pollen release direction and scattering angle was studied to determine the plant's reproductive strategy. Medium‐sized to large bees sonicated flowers in a specific position, and the probability of pollen transfer correlated with bee size even among these legitimate visitors. Small bees acted as pollen thieves or robbers. Anther rostrum and pore morphology serve to direct and focus the pollen jet released by floral sonication towards the pollinator's body. Resulting from the ventral and dorsal positioning of the short and long stamens, respectively, the pollinator's body was widely covered with pollen. This improves the plant's chances of outcrossing, irrespective of which bee body part contacts the stigma. Consequently, R. grandiflora is also able to employ bee species of various sizes as pollen vectors. The strategy of spreading pollen all over the pollinator's body is rather cost‐intensive but counterbalanced by ensuring that most of the released pollen is in fact transferred to the bee. Thus, flowers of R. grandiflora illustrate how specialized morphology may serve to improve pollination by a functional group of pollinators.