Pollination and reproduction of Psychotria homalosperma,an endangered distylous tree endemic to the oceanic Bonin (Ogasawara) Islands,Japan

Distyly is usually rare or not observed in species thriving on oceanic islands. The rarity of this breeding system is probably because of the difficulty of colonization for distylous plants and the paucity of pollinators on oceanic islands. However, the endemic and endangered tree Psychotria homalosperma has maintained its distylous nature in the oceanic Bonin Islands, Japan. To understand how the distylous breeding system of P. homalosperma has been maintained on these islands and to characterize the reproduction systems, we studied the pollination and reproductive biology of this species. Specifically, we observed current flower visitors and estimated their effects on plant reproduction. We also examined the floral traits and floral volatiles of P. homalosperma to infer its original pollinators, because plant–pollinator relationships in the Bonin Islands have recently been disrupted by anthropological activities. Finally, we examined the fruit set and pollen tube growth in the stigmas under hand and open pollination. Although original pollinators were presumed to be moths with long proboscises, the introduced honeybee, Apis mellifera, was the most common flower visitor. The honeybee carried pollen grains only unidirectionally, from the short‐ to long‐styled morphs, because it could not reach the hidden stigmas of the short‐styled flowers, and long‐styled flowers set fruits 1.7–38 times more than short‐styled ones. This case study indicates that the instability of pollinator fauna can cause distylous species to be rare on oceanic islands.     

Identification of effective pollinators of Primula sieboldii E. Morren in a wild habitat in Hiroshima,Japan

Primula sieboldii E. Morren is a heterostylous clonal herb that is widely distributed in Japan but in danger of extinction in the wild. The existence of pollinators in each habitat is imperative for its long-term survival, because seeds can be produced only by insect cross-pollination between different flower morphs. In this study, we identified the pollinators of P. sieboldii in a wild habitat in Hiroshima as those insects that we observed to (a) put the proboscis into a corolla tube, (b) deposit pollen grains on the proboscis, and (c) have a proboscis of appropriate length and width. Effective pollinators were identified from their contribution to pollination. In 2015 and 2016, the flower visitations of 232 and 558 insects, respectively, were recorded and 85 and 13 insects were captured. Two Bombylius species, B. major L. and B. shibakawae Matsumura, accounted for 90% of flower-visiting insects in both years. All 14 species that we captured were considered pollinators of P. sieboldii, because they had proboscises that were long enough to reach pollen and that had pollen grains deposited on them. The total visitation rate of “Bombyliidae” was the highest among all pollinator categories. The results of potential pollen transport per flower per hour, which was based on total pollen number and total visitation rate of each pollinator category, indicated that “Bombyliidae” species were the most effective pollinators of P. sieboldii in this habitat.     

THE POLLINATION ECOLOGY OF PEDICULARIS ON MOUNT RAINIER

Six native species of Pedicularis in Mount Rainier National Park in Washington State were studied for their reproductive relationships with animal pollinators. Cinematographic and stereophotographic records revealed pollination of the nectariferous P. bracteosa and P. rainierensis by upright, nectar-foraging queens and workers of five bumblebee (Bombus Latr.) species and by inverted workers scraping pollen from anthers concealed within the corolla galea. The nectarless, rostrate flowers of P. contorta, P. groenlandica, P. ornithorhyncha, and P. racemosa were pollinated by pollen-foraging workers and occasional queens virbrating pollen from concealed anthers. Insect exclosure methods revealed complete absence of fruiting in the absence of insects, and pollinator collections further indicate obligate dependence of the plants upon bumblebees for their sexual reproduction. Analysis of corbicular pollen loads from pollinators suggested that pollinator species are not monolectic but that individual pollinators range from monolectic to polylectic. Measurements indicated limited correlations between lengths of corolla tubes and tongues of nectar-foraging insects. Each nectarless Pedicularis species occupied a different, specific habitat, but P. bracteosa and the endemic P. rainierensis were sympatric in part. Each species had a unique spectral reflectance pattern from the corolla. Proximity of habitats and overlap of blooming periods of all Pedicularis species eliminate the possibility of contemporary geographic or phenological reproductive isolation. It is suggested that behavioral interactions of the plants and their insect pollinators may have been instrumental in the past in reproductively isolating these species, hybrids of which are unknown.     

A preliminary study on pollination biology of Omphalogramma souliei Franch. (Primulaceae), a species endemic to China

The pollination biology of Omphalogramma souliei Franch., a species endemic to southwestern China, was investigated. Floral phenology, flower visitors, pollen/ovule ratio, attractants and rewards to the visitors were observed, measured, and recorded. Bagging experiments to exclude pollinators were carried out in the wild for two years. Our results revealed five important aspects of the reproductive biology of Omphalogramma souliei. 1) The pollen-ovule ratio was 1748±233. The breeding system was self-compatible, with facultative xenogamy. 2) The pollination syndrome is entomophily, and this species could not be pollinated by wind if the pollinators were unavailable. 3) Six insect species were observed visiting the flowers of Omphalogramma souliei in the wild, of them, three species of hymenoptera, Lasioglossum sp., Heriades parvula Cockerell and Micrapis florae Fabricius, are the principal floral visitors and effective pollinators. 4) The visual attractants to the visitors are floral color and shape, the large yellow anthers, and the rewards for visitors are pollen and nectar. 5) Cleistogamy may also occur, since the anthers of some flowers dehisced before opening of the corolla. The results of floral biology and pollination characters suggest that xenogamy predominated and autogamy played an assistant role in the evolution of reproduction and breeding system of O. souliei.     

Pollenfertility and seed formation in theOrnithogalum umbellatum/angustifolium complex (Liliaceae/Scilloideae)

The pollen fertility and seed formation of six species of theOrnithogalum umbellatum/angustifolium complex and of seven related species were studied. Four types of pollen grains could be recognized. The pollen fertility varied greatly in this complex and is not related to the ploidy level. The seed formation ofO. umbellatum showed an adaptation to a subcontinental-Mediterranean climate, that ofO. angustifolium to an Atlantic climate. In both cases raindrops seem to be important for pollination, in view of the absence of insect pollinators. After open pollination 113 seedlings were obtained in four species. Their chromosome numbers were determined. Nearly all the cultivated seedlings were aneuploid, which points to a positive selection of euploids in nature, because aneuploid individuals are rare in the wild.Biosystematic Studies on theOrnithogalum umbellatum/angustifolium Complex III.—Previous parts of this series are Part I: Taxonomy. Proceeding Kon. Ned. Acad. Wet. series C,85 (4), 563–574 (1982) andvan Raamsdonk (1984).     

Pollination niche overlap between a parasitic plant and its host

Niche theory predicts that species which share resources should evolve strategies to minimise competition for those resources, or the less competitive species would be extirpated. Some plant species are constrained to co-occur, for example parasitic plants and their hosts, and may overlap in their pollination niche if they flower at the same time and attract the same pollinators. Using field observations and experiments between 1996 and 2006, we tested a series of hypotheses regarding pollination niche overlap between a specialist parasitic plant Orobanche elatior (Orobanchaceae) and its host Centaurea scabiosa (Asteraceae). These species flower more or less at the same time, with some year-to-year variation. The host is pollinated by a diverse range of insects, which vary in their effectiveness, whilst the parasite is pollinated by a single species of bumblebee, Bombus pascuorum, which is also an effective pollinator of the host plant. The two species therefore have partially overlapping pollination niches. These niches are not finely subdivided by differential pollen placement, or by diurnal segregation of the niches. We therefore found no evidence of character displacement within the pollination niches of these species, possibly because pollinators are not a limiting resource for these plants. Direct observation of pollinator movements, coupled with experimental manipulations of host plant inflorescence density, showed that Bombus pascuorum only rarely moves between inflorescences of the host and the parasite and therefore the presence of one plant is unlikely to be facilitating pollination in the other. This is the first detailed examination of pollination niche overlap in a plant parasite system and we suggest avenues for future research in relation to pollination and other shared interactions between parasitic plants and their hosts.     

Floral traits mediate the vulnerability of aloes to pollen theft and inefficient pollination by bees

Background and Aims

Pollen-collecting bees are among the most important pollinators globally, but are also the most common pollen thieves and can significantly reduce plant reproduction. The pollination efficiency of pollen collectors depends on the frequency of their visits to female(-phase) flowers, contact with stigmas and deposition of pollen of sufficient quantity and quality to fertilize ovules. Here we investigate the relative importance of these components, and the hypothesis that floral and inflorescence characteristics mediate the pollination role of pollen collection by bees.

Methods

For ten Aloe species that differ extensively in floral and inflorescence traits, we experimentally excluded potential bird pollinators to quantify the contributions of insect visitors to pollen removal, pollen deposition and seed production. We measured corolla width and depth to determine nectar accessibility, and the phenology of anther dehiscence and stigma receptivity to quantify herkogamy and dichogamy. Further, we compiled all published bird-exclusion studies of aloes, and compared insect pollination success with floral morphology.

Key Results

Species varied from exclusively insect pollinated, to exclusively bird pollinated but subject to extensive pollen theft by insects. Nectar inaccessibility and strong dichogamy inhibited pollination by pollen-collecting bees by discouraging visits to female-phase (i.e. pollenless) flowers. For species with large inflorescences of pollen-rich flowers, pollen collectors successfully deposited pollen, but of such low quality (probably self-pollen) that they made almost no contribution to seed set. Indeed, considering all published bird-exclusion studies (17 species in total), insect pollination efficiency varied significantly with floral shape.

Conclusions

Species-specific floral and inflorescence characteristics, especially nectar accessibility and dichogamy, control the efficiency of pollen-collecting bees as pollinators of aloes.     

Interspecific pollen transfer as a mechanism of competition: Consequences of foreign pollen contamination for seed set in the alpine wildflower,Polemonium viscosum

Summary Earlier studies showed that under natural conditions foreign pollen receipt is correlated with loss of seed set in populations of P. viscosum. Here, we report on experimental pollinations using foreign pollen from two co-flowering species that share pollinators with P. viscosum. Experiments were designed to ascertain whether improper pollen transfer causes reduced seed set under controlled conditions and, if so, to determine the stage at which interference occurs. In flowers pre-treated by pollination with either Mertensia or Castilleja pollen, adherence of subsequently deposited conspecific pollen grains was unaffected. However, conspecific grains had significantly lower germination and ovule fertilization success in flowers receiving foreign pollen than in controls. These results suggest that pollinator infidelity in high alpine plant communities can reduce female reproductive success of P. viscosum by inhibiting the performance of conspecific pollen grains. Negative effects of Mertensia and Castilleja pollen were comparable despite large interspecific differences in pollen grain morphology. Accordingly, susceptibility to foreign pollen interference appears to be an intrinsic property of P. viscosum that is not dependent on the unique structural properties of pollen produced by competitive species.     

牛耳朵传粉生物学研究

苦苣苔科(Gesneriaceae)报春苣苔属(Primulina Hance)是一个近年来备受关注的类群,其纷繁复杂的物种多样性和属下种间的特有分布引起了分类学家和植物学研究者的极大兴趣。该属除了极少数的物种如牛耳朵[(Primulina eburnea (Hance) Y. Z. Wang)]以外,绝大部分的物种为狭域分布或地方特有种,其分布范围很窄。为了揭示牛耳朵的传粉生物学和繁育系统对其生殖过程和拓殖能力的影响机制,作者系统地研究了牛耳朵的开花物候、花粉与柱头活性、访花昆虫的种类和访花行为、花粉胚珠比、OCI指数和套袋实验结实率,探究其传粉等生殖过程对牛耳朵的广布是否有正面影响。结果表明:牛耳朵的自然花期是3—5月,全花期约45 d,其中盛花期约20 d,单花期6～8 d;开花后1～2 d花粉活力最强,开花前柱头没有可授性;花粉胚珠比为537;杂交指数为5;去雌套袋、去雄套袋均无法结实,说明本种不存在无融合生殖;与自然授粉相比,自花授粉结实率略低,异花授粉结实率略高,说明自交亲和;牛耳朵的主要传粉者是花条蜂(Anthophora florea)和熊蜂(Bombus sp.)。花蜜产量较高、花粉量较大、花粉活力较强等特点,有利于牛耳朵完成传粉和结实的整个繁殖过程。因此,这一结果显然有利于牛耳朵的拓殖进而广布在我国华南至西南地区的喀斯特地区。     

牛耳朵传粉生物学研究

苦苣苔科(Gesneriaceae)报春苣苔属(Primulina Hance)是一个近年来备受关注的类群,其纷繁复杂的物种多样性和属下种间的特有分布引起了分类学家和植物学研究者的极大兴趣。该属除了极少数的物种如牛耳朵[(Primulina eburnea(Hance)Y. Z. Wang)]以外,绝大部分的物种为狭域分布或地方特有种,其分布范围很窄。为了揭示牛耳朵的传粉生物学和繁育系统对其生殖过程和拓殖能力的影响机制,作者系统地研究了牛耳朵的开花物候、花粉与柱头活性、访花昆虫的种类和访花行为、花粉胚珠比、OCI指数和套袋实验结实率,探究其传粉等生殖过程对牛耳朵的广布是否有正面影响。结果表明:牛耳朵的自然花期是3—5月,全花期约45 d,其中盛花期约20 d,单花期6～8 d; 开花后1～2 d花粉活力最强,开花前柱头没有可授性; 花粉胚珠比为537; 杂交指数为5; 去雌套袋、去雄套袋均无法结实,说明本种不存在无融合生殖; 与自然授粉相比,自花授粉结实率略低,异花授粉结实率略高,说明自交亲和; 牛耳朵的主要传粉者是花条蜂(Anthophora florea)和熊蜂(Bombus sp.)。花蜜产量较高、花粉量较大、花粉活力较强等特点,有利于牛耳朵完成传粉和结实的整个繁殖过程。因此,这一结果显然有利于牛耳朵的拓殖进而广布在我国华南至西南地区的喀斯特地区。     

Pollination of Aristolochia pallida Willd. (Aristolochiaceae) in the Mediterranean

A first study of the pollination biology of a Mediterranean Aristolochia species in its natural habitat is presented. In all, 183 flowers of Aristolochia pallida Willd. were investigated, which in total contained 73 arthropods, dominated by two groups of Diptera, black fungus gnats (Sciaridae representing 37%) and scuttle flies (Phoridae representing 19%), respectively. However, only Phoridae are regarded as potential pollinators, since pollen has been found exclusively on the body of these insects. All Phoridae belong to the genus Megaselia and are recognised as three morpho-species. The measurements of flower and insect dimensions suggest that size is an important constraint for successful pollination: (a) the insects must have a definitive size for being able to enter the flower and (b) must be able to get in touch with the pollen. Only very few insect groups found in A. pallida fulfil these size requirements. However, size alone is not a sufficient filter as too many fly species of the same size might be trapped but not function as pollinators. Instead, specific attraction is required as otherwise pollen is lost. Since all trapped Phoridae are males, a chemical attraction (pheromones) is proposed as an additional constraint. Since the flowers are protogynous, the record of Megaselia loaded with pollen found in a flower during its female stage proves that this insect must have had visited at least one different flower during its male stage before. Further on, this observation provides strong evidence that the flowers are cross-pollinated. All these factors indicate a highly specialised pollination of A. pallida by Megaselia species.     

The pollination ecology of Pedicularis rex subsp. lipkyana and P. rex subsp. rex (Orobanchaceae) from Sichuan, southwestern China

Pedicularis is one of few genera for which pollination ecology has been studied extensively. Although over half of the species of Pedicularis are found in the mountains of southwestern China, pollination ecology has been studied there on a few species only. The present paper reports pollination ecology of Pedicularis rex subsp. lipskyana and P. rex subsp. rex from Sichuan, southwestern China. The two subspecies are nectariferous, with sugar content 28% in P. rex lipskyana and 22% in P. rex, respectively. The flowers of the two subspecies are adapted to pollination by bumblebee workers. Bumblebees are the primary and effective pollinators although honeybees were also observed pollinating P. rex subsp. lipskyana at one studied population. Usually bumblebees entered the corolla tube from the right side in an upright or a nearly half-inverted position to imbibe nectar located at the base of the corolla tube. The stigma usually contacts the side region of the thorax and abdomen or occasionally directly contacted pollen loads, leading to pollination of flowers. Much less commonly, bumblebees foraged on flowers of P. rex subsp. rex in an inverted position for pollen, which pollinated flowers sternotribically. We suggest that pollination mechanism is closely associated with floral morphology. Some important differences were found from a previous study on P. rex in floral morphology and the primary pollination mechanism.     

Effectiveness of buzz pollination in Pedicularis chamissonis: significance of multiple visits by bumblebees

Pollination success of plants is highly susceptible to the frequency of visits and foraging behavior of pollinators. Pollination of the nectarless flowers of Pedicularis species depends on bumblebee workers collecting pollen by vibrating the anthers (buzz pollination). However, little is known about the efficiency of the pollination system. Foraging behavior, pollen removal from anthers and pollen deposition on stigmas of P. chamissonis were studied to assess the effectiveness of buzz pollination in an alpine snowbed population of northern Japan. Although bumblebees tended to visit most of the flowers open at a given time within inflorescences during a single visit, pollen removal rate at the first visit was about 20%, and buzzing period decreased with increasing number of previous visits, resulting in a decreasing proportion of pollen removed per visit as the number of visits increased. These trends enable plants to provide pollen for more pollinators. The number of pollen grains deposited on stigmas was not saturated during the first visit and increased with additional visits. Irrespective of weak self-compatibility, evidence of interference between self and outcross pollen was lacking for seed production. Therefore, buzz pollination in P. chamissonis acts as a mechanism that improves the chance of cross-pollination upon multiple visits if pollinator visitation is frequent.     

蛛网萼开花物候、花部特征及繁育系统研究

为探讨蛛网萼(Platycrater arguta)传粉生物学特性,该研究以江西上饶广丰铜钹山国家级自然保护区、江西阳际峰国家级自然保护区蛛网萼为材料,采用野外观察和人工授粉等方法,对蛛网萼开花物候、花部形态及繁育系统进行了研究。结果表明:(1)蛛网萼为伞形花序,种群花期一般在6月中下旬至8月中旬,单花花期为2~3 d,花序花期持续10 d。两个保护区由于年均温度与光照的不同,花期进程有显著不同。(2)蛛网萼可孕花与不孕花从绿色变为白色时对访花昆虫有吸引作用,不孕花能够增加昆虫的访花频率。(3)蛛网萼花粉胚珠比(P/O)为2 520~3 100,杂交指数即是3或4。(4)繁育体系属于以异交为主,部分自交亲和,需要传粉者;熊蜂(Bombus sp.)、四条蜂(Apis florea)和油茶地蜂(Andrena cammelia)是蛛网萼的有效传粉昆虫。(5)套袋和人工授粉结果显示,蛛网萼为兼性自交和异交授粉,异株异花授粉能显著提高坐果率及结籽率,这主要与生境中有效传粉昆虫种类、数量少,花粉传递效率低,种群间基因流交流降低以及柱头自花及同株异花传粉等有关,从而表明在蛛网萼现有生境中植株的早期生殖成功受到影响。蛛网萼种群分布范围扩张以有性繁殖为主,无性繁殖作为重要补充及繁殖保障。     

First record of potential bird pollination in the holoparasitic genus Orobanche L.

Pollinators play an important role in the reproduction of zoophilous plants. A shift in pollinators has often been observed for oceanic island plants, probably because of the differences in fauna. In this study, we obtained data on pollinator shifts from insects to birds in Orobanche boninsimae (Orobanchaceae), a holoparasitic plant species endemic to the Bonin (Ogasawara) Islands, oceanic islands in the Pacific. We observed pollination and measured seed viability in O. boninsimae and its continental sister species O. coerulescens. We found that two passerine birds, the Japanese white-eye (Zosterops japonicus) and bulbul (Hypsipetes amaurotis squameiceps), visited the flowers and sucked the nectar of O. boninsimae, while only insects visited those of O. coerulescens. Viable seeds were produced under pollinator-excluded treatments in the two Orobanche species, indicating that the seeds were produced by automatic self-pollination and/or apomixis. These results suggest that O. boninsimae may be pollinated by birds and can produce seeds by automatic self-pollination/apomixis. This is the first record of visitation of the genus Orobanche by birds. Studies of pollination systems in native plants on the Bonin Islands are few compared to those on other oceanic islands, and O. boninsimae may provide a valuable example of pollinator shifts in the Bonin Islands.     

Reproductive biology ofAsphodelus aestivus (Asphodelaceae)

InAsphodelus aestivus the large number of showy flowers opened per inflorescence, high nectar and pollen production, and absence of automatic self-pollination, so that insect visitation is necessary for pollination, indicate that cross-fertilization is favoured. LargeHymenoptera are the main pollinators. Hand self-pollinations result in some degree of fruit-set, but cross-pollination also yield low fruit- and seed-set. The perennial habit and polyploid status are in agreement with the breeding system of this species, with sexual reproduction being rather inefficient and active vegetative propagation.     

Insect-induced wind pollination of the palm Chamaedorea pinnatifrons and pollination in the related Wendlandiella sp.

In Peruvian Amazonia pollination ecology of two palms, Chamaedorea pinnatifrons (Jacq.) Oerst. and Wendlandiella sp. was studied from October 1988 to January 1990. Both palms are dioecious understory species that form locally dense populations.In C. pinnatifrons both sexes flower synchronously during the dry season. Prior to anthesis, the pendulous male inflorescence is inhabited by numerous thrips (Thysanoptera) and Ptiliidae (Coleoptera). Staminate flowers open by a small basal slit between the petals. At anthesis pollen is shed and the movements of the insects inside the flowers trigger pollen release in small clouds. Thus, the powdery pollen becomes airborne and finally air currents act as a vector, carrying pollen to the inconspicuous female plants, which usually are not visited by insects. The term insect induced wind pollination is suggested for this pollination mode. Wendlandiella flowers during four months in the dry season. Male and female plants were not visited by insects. The dry condition of the pollen indicates that anemophily is the pollination mode in Wendlandiella. Fructification is rare but the plants show intense vegetative propagation.The significance of anemophily in the tropical lowland rain forest is discussed.     

Evidence for beetle pollination in the African grassland sugarbushes (Protea: Proteaceae)

Most lineages in the African genus Protea consist of species with large unscented flowers pollinated principally by birds, and several of these lineages also show evidence of shifts to rodent pollination, associated with concealed yeasty-scented flowerheads. In this study we investigated the hypothesis that brightly coloured and fruity-scented flowerheads of four Protea species (P. caffra, P. simplex, P. dracomontana and P. welwitschii) represent a novel shift from bird to insect pollination in a grassland lineage in the genus. These species are visited by a wide range of insects, but cetoniine beetles were found to be the most important pollinators because of their abundance, size and relatively pure pollen loads. Three of the four putatively insect-pollinated Protea species have flowers presented at ground level, and experiments showed that cetoniine beetles preferred inflorescences at ground level to those artificially elevated to the height of shrubs and small trees. Relative to insects, birds were infrequent visitors to all of the study species. The nectar of all the study species contained xylose, as documented previously in bird- and rodent-pollinated Protea species, suggesting that this is a phylogenetically conserved trait. However, the very low concentration of nectar (ca. 8%), short nectar-stigma distance and the fruity scent of florets appear to be traits that are associated with specialisation for pollination by cetoniine beetles.     

Seasonal and annual variations in the pollination efficiency of a pollinator community of Dictamnus albus L.

The interplay between insect and plant traits outlines the patterns of pollen transfer and the subsequent plant reproductive fitness. We studied the factors that affect the pollination efficiency of a pollinator community of Dictamnus albus L. by evaluating insect behaviour and morphological characteristics in relation to flowering phenology. In order to extrapolate the pollinator importance of single taxa and of the whole pollinator guild, we calculated an index distinguishing between potential (PPI) and realized (RPI) pollinator importance. Although the pollinator species spectrum appeared rather constant, we found high intra‐ and inter‐annual variability of pollinator frequency and importance within the insect community. Flower visitation rate strictly depended on insect abundance and on the overlap between their flying period and flower blooming. All the pollinators visited flowers from the bottom to the top of the racemes, excluding intra‐plant geitonogamous pollination, and most of them showed high pollen fidelity. Only medium large‐sized bees could contact the upward bending stiles while feeding on nectar, highlighting a specialisation of the plant towards bigger pollinators. Moreover, we found evidence of functional specialisation, since all pollinators were restricted to a single taxonomic group (order: Hymenoptera; superfamily: Apoidea). Both the PPI and RPI indices indicate Habropoda tarsata as the most important pollinator of D. albus. Following hand cross‐pollination experiments we revealed the presence of pollination limitation in 1 of the 3 years of field study. We discuss this result in relation to flowering abundance and to possible mismatches of phenological periods between plants and insects.     

Bird and insect pollinators differ in specialization and potential pollination services along disturbance and resource gradients

Combined studies of the communities and interaction networks of bird and insect pollinators are rare, especially along environmental gradients. Here, we determined how disturbance by fire and variation in sugar resources shape pollinator communities and interactions between plants and their pollinating insects and birds. We recorded insect and bird visits to 21 Protea species across 21 study sites and for 2 years in Fynbos ecosystems in the Western Cape, South Africa. We recorded morphological traits of all pollinator species (41 insect and nine bird species). For each site, we obtained estimates of the time since the last fire (range: 2–25 calendar years) and the Protea nectar sugar amount per hectare (range: 74–62 000 g/ha). We tested how post-fire age and sugar amount influence the total interaction frequency, species richness and functional diversity of pollinator communities, as well as pollinator specialization (the effective number of plant partners) and potential pollination services (pollination service index) of insects and birds. We found little variation in the total interaction frequency, species richness and functional diversity of insect and bird pollinator communities, but insect species richness increased with post-fire age. Pollinator specialization and potential pollination services of insects and birds varied differently along the environmental gradients. Bird pollinators visited fewer Protea species at sites with high sugar amount, while there was no such trend for insects. Potential pollination services of insect pollinators to Protea species decreased with increasing post-fire age and resource amounts, whereas potential pollination services of birds remained constant along the environmental gradients. Despite little changes in pollinator communities, our analyses reveal that insect and bird pollinators differ in their specialization on Protea species and show distinct responses to disturbance and resource gradients. Our comparative study of bird and insect pollinators demonstrates that birds may be able to provide more stable pollination services than insects.