Exploring the boundary between pollination syndromes: bats and hummingbirds as pollinators of<Emphasis Type="Italic"> Burmeistera cyclostigmata</Emphasis> and<Emphasis Type="Italic"> B. tenuiflora</Emphasis> (Campanulaceae)

In this study I documented the degree of specialization in the pollination systems of Burmeistera cyclostigmata and B. tenuiflora (Campanulaceae) to explore the potential role of floral isolation in the diversification of the genus. I asked which floral characteristics are important in specializing on either bat or hummingbird pollination, and whether overlap between these floral syndromes can exist. I examined nocturnal and diurnal pollen deposition, pollinator visitation rates, and single visit effectiveness and related them to intra- and interspecific variation in Burmeistera floral characteristics at Monteverde, Costa Rica. Bats and hummingbirds visited both Burmeistera species, and bats pollinated both species. Owing to differences in floral morphology, however, hummingbirds effectively pollinated only B. tenuiflora. The generalized pollination system of B. tenuiflora demonstrates that there can be overlap in the boundary between ornithophily and chiropterophily, and that nectar production and timing of anthesis do not serve as barriers between these syndromes. The high intraspecific variation in floral color from green to red or purple did not correlate with either nocturnal or diurnal pollen deposition. Degree of flower accessibility did affect pollination; nocturnal pollen deposition significantly decreased as flowers become more obstructed. In Burmeistera, floral morphology and accessibility appear to be the most important floral characteristics for specialization at the boundary between ornithophily and chiropterophily.     

Change of floral orientation affects pollinator diversity and their relative importance in an alpine plant with generalized pollination system,Geranium refractum (Geraniaceae)

Floral orientation may affect pollinator attraction and pollination effectiveness, and its influences may differ among pollinator species. We, therefore, hypothesized that, for plant species with a generalized pollination system, changes in floral orientation would affect the composition of pollinators and their relative contribution to pollination. Geranium refractum, an alpine plant with downward floral orientation was used in this study. We created upward-facing flowers by altering the flower angle. We compared the pollinator diversity, pollination effectiveness, and pollinator importance, as well as female reproductive success between flowers with downward- and upward-facing orientation. Results indicated that the upward-facing flowers were visited by a wider spectrum of pollinators (classified into functional groups), with higher pollinator diversity than natural flowers. Moreover, due to influences on visitation number and pollen removal, the pollinator importance exhibited by the main pollinator groups differed between flower types. Compared with natural flowers, the pollination contribution of principal pollinators (i.e., bumblebees) decreased in upward-facing flowers and other infrequent pollinators, such as solitary bees and muscoid flies, removed more pollen. Consequently, stigmatic pollen loads were lower in upward- than in downward-facing flowers. These findings reveal that floral orientation may affect the level of generalization of a pollination system and the relative importance of diverse pollinators. In this species, the natural downward-facing floral orientation may increase pollen transfer by effective pollinators and reduce interference by inferior pollinators.     

Pollination biology of two chiropterophilous agaves in Arizona

I studied the pollination biology of two closely related species of agave, Agave palmeri and A. chrysantha (Agavaceae), which exhibit several chiropterophilous (bat-pollinated) traits. Floral studies, floral visitor observations, and pollination studies were conducted over four summers at six different sites to examine floral traits and determine the relative importance of diurnal vs. nocturnal pollinators. Agave chrysantha appears to have developed minor shifts in several floral characters that enhance diurnal pollination. Although floral shifts towards diurnal pollination were fewer in A. palmeri, stigmas were diurnally receptive and copious floral rewards were available in the morning, indicating that some adaptations exist to allow for multiple pollinators. Differences in fruit and seed set between naturally day- and night-pollinated umbels for both species were either not significant or significantly higher in day-pollinated plants. Bats were not important pollinators of A. chrysantha, and the mutualistic relationship between A. palmeri and the lesser long-nosed bat was found to be asymmetric. "Bat-adapted" floral traits appear to be flexible enough to respond to the climatic and pollinator unpredictability experienced by agaves at the northern edge of their distribution. This variability may be a more important factor affecting evolution of floral characters than a particular pollinator.     

Many to flower, few to fruit: the reproductive biology of Hamamelis virginiana (Hamamelidaceae)

Hamamelis virginiana flowers from late September to late November. In 1977, we began studying the reproductive biology of this eastern North American arborescent shrub by examining floral phenology and rewards, pollen-ovule ratios, breeding system, pollination, pollinator and resource limitation, and seed dispersal. The homogamous, self-incompatible flowers emit a faint odor, bear nectar with sucrose ratios typical of bee- and fly-pollinated flowers, and produce abundant sticky pollen. Flowers were visited infrequently by insects representing six orders. Flies were the most common floral visitors, specifically members of the genus Bradysia, but small bees also carried high percentages of Hamamelis pollen. Despite high pollen/ovule ratios (11?445 grains/ovule), bees and flies are likely pollinators, as experiments indicate wind pollination is less likely. Pollen quantity and resource availability did not appear to limit reproductive output, but pollen quality did. Tests of >40?000 flowers showed natural fruit set to be <1%. The flowering time, breeding system, and clumped distribution of plants, likely due in part to limited seed dispersal, combine to yield this remarkably low fruit set. Because all other species of Hamamelis flower from late winter to early summer, it may be that H. virginiana evolved a fall flowering phenology to avoid competition for pollinators with the closely related H. vernalis.     

Floral divergence, pollinator partitioning and the spatiotemporal pattern of plant–pollinator interactions in three sympatric Adenophora species

Floral divergence among congeners may relate to differential utilization of pollinators and contribute to reducing overlap in pollination niches. To investigate whether and how floral differences are associated with differential utilization of pollinators in three sympatric Adenophora species, we analyzed floral traits and evaluated the contribution of different visitors to pollination. We compared visitation rates of different pollinator categories in different years and sites. A suite of floral traits differed among the three Adenophora species, suggesting adaptation to diurnal versus nocturnal pollination and an intermediate condition. However, many visitor species were shared among the three plant species, suggesting that floral traits did not rigorously filter visitors. Effective pollinators were large bees and moths. The importance of large bees as pollinators decreased whereas that of moths increased along the gradient from typically bee-pollinated to moth-pollinated flowers. The intermediate species (A. khasiana) differed substantially from the other two species in pollinator species but not in pollinator categories. The principal pollinator category of each species was constant across years and sites except in the intermediate species where it differed between two sites. Overall, the three sympatric species of Adenophora partition pollinators by floral divergence and the principal pollinators coincide with the predictions based on floral syndromes.     

马先蒿属花冠形态的多样性与传粉式样的关系

马先蒿属(Pediculais)是有花植物中花冠形态多样化最为集中的属。该属主要的传粉者是熊蜂属(Bormbus)昆虫;在北美,熊蜂和蜂鸟是马先蒿植物一些种类有效的传粉者;也发现壁蜂(Osmia)为其传粉。不同的传粉机制要求某一特定的取食式样储藏和释放花粉。本文讨论了花冠类型的进化趋势与传粉式样和花粉形态的关系。传粉者的选择压力是决定花冠多样化的重要因素之一;花冠类型与传粉者和传粉行为紧密相关。马先蒿植物和传粉者的相互依赖与其花冠类型、功能和物候互相适应,但花冠类型与花粉形态两者之间似乎没有明显的一一对应关系。通过北美、日本和喜马拉雅不同地理分布马先蒿种类的比较研究表明,具有相同花冠类型的种类有着相同的传粉方式,花冠形态与传粉式样存在紧密的协同进化关系。     

Are pollinators the agents of selection on flower colour and size in irises?

Plant–pollinator interactions are believed to play a major role in the evolution of floral traits. Flower colour and flower size are important for attracting pollinators, directly influencing reproduction, and thus expected to be under pollinator‐mediated selection. Pollinator‐mediated selection is also proposed to play a role in maintaining flower colour polymorphism within populations. However, pigment concentrations, and thus flower colour, are also under selective pressures independent of pollinators. We quantified phenotypic pollinator‐mediated selection on flower colour and size in two colour polymorphic Iris species. Using female fitness, we estimated phenotypic selection on flower colour and size, and tested for pollinator‐mediated selection by comparing selection gradients between flowers open to natural pollination and supplementary pollinated flowers. In both species, we found evidence for pollen limitation, which set the base for pollinator‐mediated selection. In the colour dimorphic Iris lutescens, while pigment concentration and flower size were found to be under selection, this was independent of pollinators. For the polymorphic Iris pumila, pigment concentration is under selective pressure by pollinators, but only for one colour morph. Our results suggest that pollinators are not the main agents of selection on floral traits in these irises, as opposed to the accepted paradigm on floral evolution. This study provides an opposing example to the largely‐accepted theory that pollinators are the major agent of selection on floral traits.     

Pollen limitation,species’ floral traits and pollinator visitation: different relationships in contrasting communities

Failures in the process of pollen transfer among conspecific plants can severely impact female reproductive success. Thus, pollen limitation can cause selection on plant mating systems and floral traits. The relationships between pollen limitation and floral traits might be partly mediated by the quantity and identity of pollinator visits. However, very little is known about the relationship between pollinator visits and pollen limitation. We examined the relationships between pollen limitation and floral traits at the community level to connect them to community ecology processes. We used 48 plant species from two contrasting communities: one species‐rich lowland community and one species‐poor alpine community. In addition, we calculated visitation rates and ecological pollination generalization for 38 of the species to examine the relationship between pollinator visitation and pollen limitation at the community level. We found low overall levels of pollen limitation that did not differ significantly between the alpine and the lowland community. In both communities, species with evolutionary specialized flowers were more pollen limited than species with unspecialized flowers. Species’ visitation rates and selfing capability were negatively related to pollen limitation in the alpine community, where pollinators are scarcer. However, flower size/number, ecological generalization of plants and flowering onset had greater effects on pollen limitation levels at the lowland community, indicating that the identity of the visitors and plant‐plant competitive interactions are more decisive for plant reproduction in this species‐rich community. There, pollen limitation increased with flower size and flowering onset, and decreased with ecological generalization, but only in species with evolutionary specialized flowers. Our study suggests that selection on plant mating system and floral traits may be idiosyncratic to each particular community and highlights the benefits of conducting community‐level studies for a better understanding of the processes underlying evolutionary responses to pollen limitation.     

Floral symmetry affects speciation rates in angiosperms

Despite much recent activity in the field of pollination biology, the extent to which animal pollinators drive the formation of new angiosperm species remains unresolved. One problem has been identifying floral adaptations that promote reproductive isolation. The evolution of a bilaterally symmetrical corolla restricts the direction of approach and movement of pollinators on and between flowers. Restricting pollinators to approaching a flower from a single direction facilitates specific placement of pollen on the pollinator. When coupled with pollinator constancy, precise pollen placement can increase the probability that pollen grains reach a compatible stigma. This has the potential to generate reproductive isolation between species, because mutations that cause changes in the placement of pollen on the pollinator may decrease gene flow between incipient species. I predict that animal-pollinated lineages that possess bilaterally symmetrical flowers should have higher speciation rates than lineages possessing radially symmetrical flowers. Using sister-group comparisons I demonstrate that bilaterally symmetric lineages tend to be more species rich than their radially symmetrical sister lineages. This study supports an important role for pollinator-mediated speciation and demonstrates that floral morphology plays a key role in angiosperm speciation.     

Acoustic traits of bat-pollinated flowers compared to flowers of other pollination syndromes and their echo-based classification using convolutional neural networks

Bat-pollinated flowers have to attract their pollinators in absence of light and therefore some species developed specialized echoic floral parts. These parts are usually concave shaped and act like acoustic retroreflectors making the flowers acoustically conspicuous to the bats. Acoustic plant specializations only have been described for two bat-pollinated species in the Neotropics and one other bat-dependent plant in South East Asia. However, it remains unclear whether other bat-pollinated plant species also show acoustic adaptations. Moreover, acoustic traits have never been compared between bat-pollinated flowers and flowers belonging to other pollination syndromes. To investigate acoustic traits of bat-pollinated flowers we recorded a dataset of 32320 flower echoes, collected from 168 individual flowers belonging to 12 different species. 6 of these species were pollinated by bats and 6 species were pollinated by insects or hummingbirds. We analyzed the spectral target strength of the flowers and trained a convolutional neural network (CNN) on the spectrograms of the flower echoes. We found that bat-pollinated flowers have a significantly higher echo target strength, independent of their size, and differ in their morphology, specifically in the lower variance of their morphological features. We found that a good classification accuracy by our CNN (up to 84%) can be achieved with only one echo/spectrogram to classify the 12 different plant species, both bat-pollinated and otherwise, with bat-pollinated flowers being easier to classify. The higher classification performance of bat-pollinated flowers can be explained by the lower variance of their morphology.     

INFLUENCE OF POLLINATION SPECIALIZATION AND BREEDING SYSTEM ON FLORAL INTEGRATION AND PHENOTYPIC VARIATION IN IPOMOEA

Natural selection should reduce phenotypic variation and increase integration of floral traits involved in placement of pollen grains on stigmas. In this study, we examine the role of pollinators and breeding system on the evolution of floral traits by comparing the patterns of floral phenotypic variances and covariances in 20 Ipomoea species that differ in their level of pollination specialization and pollinator dependence incorporating phylogenetic relatedness. Plants with specialized pollination (i.e., those pollinated by one functional group or by few morphospecies) displayed less phenotypic variation and greater floral integration than generalist plants. Self‐compatible species also displayed greater floral integration than self‐incompatible species. Floral traits involved in pollen placement and pick up showed less variation and greater integration than floral traits involved in pollinator attraction. Analytical models indicate that both breeding system and the number of morphospecies had significant effects on floral integration patterns although only differences in the former were significant after accounting for phylogeny. These results suggest that specialist/self‐compatible plants experience more consistent selection on floral traits than generalist/self‐incompatible plants. Furthermore, pollinators and breeding system promote integration of floral traits involved in pollen placement and pick up rather than integration of the whole flower.     

Incomplete partitioning of pollinators by Linum suffruticosum and its coflowering congeners

Premise

Linum suffruticosum shows variations in pollinator fit, pollen pickup, and local pollinators that predict pollen deposition rates. The species often coflowers with other Linum species using the same pollinators. We investigated whether L. suffruticosum trait variation could be explained by local patterns of pollinator sharing and associated evolution to reduce interspecific pollen transfer.

Methods

Pollinator observations were made in different localities (single species, coflowering with other congeners). Floral traits were measured to detect differences across populations and from coflowering species. Reproductive costs were quantified using interspecific hand pollinations and measures of pollen-tube formation, combined with observations of pollen arrival on stigmas and pollen-tube formation after natural pollination in allopatric and sympatric localities.

Results

The size and identity of the most important pollinator of L. suffruticosum and whether there was pollinator sharing with coflowering species appeared to explain floral trait variation related to pollinator fit. The morphological overlap of the flowers of L. suffruticosum with those of coflowering species varied, depending on coflowering species identity. A post-pollination incompatibility system maintains reproductive isolation, but conspecific pollen-tube formation was lower after heterospecific pollination. Under natural pollination at sites of coflowering with congeners, conspecific pollen-tube formation was lower than at single-species localities.

Conclusions

Trait variation in L. suffruticosum appears to respond to the most important local pollinator. Locally, incomplete pollinator partitioning might cause interspecific pollination, imposing reproductive costs. These reproductive costs may generate selection on floral traits for reduced morphological overlap with coflowering congeners, leading to the evolution of pollination ecotypes.     

Aristolochia spp. (Aristolochiaceae) pollinated by flies breeding on decomposing flowers in Panama

This study presents breeding and pollination systems of Aristolochia maxima and A. inflata in a seasonal tropical forest of Panama. Aristolochia is the most diverse genus of Aristolochiaceae, with ～120 species distributed throughout the tropics and subtropics. All the Aristolochia species studied so far are pollinated by saprophagous flies of different families, which are presumably deceived by floral odor. Flowers of many species have trap-and-release mechanisms. The flowers attract and imprison pollinators during the female stage first day of flowering and release them after anther dehiscence. Pollination systems of A. maxima and A. inflata are different from those of other Aristolochia in lacking trap mechanisms. Furthermore, the pollinators oviposit in the flowers, and their larvae grow on the fallen, decaying flowers on the ground. Therefore, the plants have a mutualistic relationship with their pollinators. Self-compatible A. inflata is pollinated by Megaselia sakaiae (Phoridae, Diptera). The pollinator may be specialized to Aristolochia flowers, which is the only substrate for larval development. On the other hand, self-incompatible A. maxima is pollinated by Drosophila spp. (Drosophilidae, Diptera), which utilize Aristolochia flowers as a breeding site only occasionally. This pollination mutualism might have evolved from deceit pollination.     

Diurnal and nocturnal pollination of Marginatocereus marginatus (Pachycereeae: Cactaceae) in Central Mexico

BACKGROUND AND AIMS: Chiropterophillous and ornithophillous characteristics can form part of a single reproductive strategy in plants that have flowers with diurnal and nocturnal anthesis. This broader pollination strategy can ensure seed set when pollinators are scarce or unpredictable. This appears to be true of hummingbirds, which presumably pollinate Marginatocereus marginatus, a columnar cactus with red nocturnal and diurnal flowers growing as part of dense bat-pollinated columnar cacti forests in arid regions of central Mexico. The aim of this study was to study the floral biology of M. marginatus, and evaluate the effectiveness of nocturnal vs. diurnal pollinators and the contribution of each pollinator group to overall plant fitness. METHODS: Individual flower buds were marked and followed to evaluate flower phenology and anthesis time. Flowers and nectar production were measured. An exclusion experiment was conducted to measure the relative contribution of nocturnal and diurnal pollinators to seed set. KEY RESULTS: Marginatocereus marginatus has red hermaphroditic flowers with nocturnal and diurnal anthesis. The plant cannot produce seeds by selfing and was pollinated during the day by hummingbirds and during the night by bats, demonstrating that both pollinator groups were important for plant reproduction. Strong pollen limitation was found in the absence of one of the pollinator guilds. CONCLUSIONS: Marginatocereus marginatus has an open pollination system in which both diurnal and nocturnal pollinators are needed to set seeds. This represents a fail-safe pollination system that can ensure both pollination, in a situation of low abundance of one of the pollinator groups (hummingbirds), and high competition for nocturnal pollinators with other columnar cacti that bloom synchronously with M. marginatus in the Tehuacan Valley, Mexico.     

Floral specialization for different pollinators and divergent use of the same pollinator among co‐occurring Impatiens species (Balsaminaceae) from Southeast Asia

Floral variation among closely related species is thought to often reflect differences in pollination systems. Flowers of the large genus Impatiens are characterized by extensive variation in colour, shape and size and in anther and stigma positioning, but studies of their pollination ecology are scarce and most lack a comparative context. Consequently, the function of floral diversity in Impatiens remains enigmatic. This study documents floral variation and pollination of seven co‐occurring Impatiens spp. in the Southeast Asian diversity hotspot. To assess whether floral trait variation reflects specialization for different pollination systems, we tested whether species depend on pollinators for reproduction, identified animals that visit flowers, determined whether these visitors play a role in pollination and quantified and compared key floral traits, including floral dimensions and nectar characteristics. Experimental exclusion of insects decreased fruit and seed set significantly for all species except I. muscicola, which also received almost no visits from animals. Most species received visits from several animals, including bees, birds, butterflies and hawkmoths, only a subset of which were effective pollinators. Impatiens psittacina, I. kerriae, I. racemosa and I. daraneenae were pollinated by bees, primarily Bombus haemorrhoidalis. Impatiens chiangdaoensis and I. santisukii had bimodal pollination systems which combined bee and lepidopteran pollination. Floral traits differed significantly among species with different pollination systems. Autogamous flowers were small and spurless, and did not produce nectar; bee‐pollinated flowers had short spurs and large floral chambers with a wide entrance; and bimodally bee‐ and lepidopteran‐pollinated species had long spurs and a small floral chamber with a narrow entrance. Nectar‐producing species with different pollination systems did not differ in nectar volume and sugar concentration. Despite the high frequency of bee pollination in co‐occurring species, individuals with a morphology suggestive of hybrid origin were rare. Variation in floral architecture, including various forms of corolla asymmetry, facilitates distinct, species‐specific pollen‐placement on visiting bees. Our results show that floral morphological diversity among Impatiens spp. is associated with both differences in functional pollinator groups and divergent use of the same pollinator. Non‐homologous mechanisms of floral asymmetry are consistent with repeated independent evolution, suggesting that competitive interactions among species with the same pollination system have been an important driver of floral variation among Impatiens spp.     

Divergence on floral traits and vertebrate pollinators of two endemic Encholirium bromeliads

Shifts in pollen vectors favour diversification of floral traits, and differences in pollination strategies between congeneric sympatric species can contribute to reproductive isolation. Divergence in flowering phenology and selfing could also reduce interspecific crossing between self‐compatible species. We investigated floral traits and visitation rates of pollinators of two sympatric Encholirium species on rocky outcrops to evaluate whether prior knowledge of floral characters could indicate actual pollinators. Data on flowering phenology, visitation rates and breeding system were used to evaluate reproductive isolation. Flowering phenology overlapped between species, but there were differences in floral characters, nectar volume and concentration. Several hummingbird species visited flowers of both Encholirium spp., but the endemic bat Lonchophylla bokermanni and an unidentified sphingid only visited E. vogelii. Pollination treatments demonstrated that E. heloisae and E. vogelii were partially self‐compatible, with weak pollen limitation to seed set. Herbivores feeding on inflorescences decreased reproductive output of both species, but for E. vogelii the damage was higher. Our results indicate that actual pollinators can be known beforehand through floral traits, in agreement with pollination syndromes stating that a set of floral traits can be associated with the attraction of specific groups of pollinators. Divergence on floral traits and pollinator assemblage indicate that shifts in pollination strategies contribute to reproductive isolation between these Encholirium species, not divergence on flowering phenology or selfing. We suggest that hummingbird pollination might be the ancestral condition in Encholirium and that evolution of bat pollination made a substantial contribution to the diversification of this clade.     

Flower biology of the cactus Coryphantha elephantidens in the tropical dry forest of Central Mexico

Floral traits and sexual systems in angiosperms are strategies that enhance outcrossing within hermaphrodite flowers and among individuals in a population. Sexual systems with unisexual flowers have also evolved among angiosperms, resulting in sex specialization. Furthermore, the interaction of floral traits and floral visitors determines successful plant reproduction. Globose cacti are bee pollinated, and variation in the diversity of their pollinator assemblages is strongly associated with floral phenotype. Our objective was to describe the floral biology of the cactus Coryphantha elephantidens and to determine its relationship with pollinators. Floral traits were studied by direct observations in live and fixed flowers. The breeding system was determined using two estimators based on floral morphology: pollen grains to ovules per flower (P/O) ratio and outcrossing index. Pollination treatments were conducted to determine the mating system. Floral visitors were recorded using direct observation. Flowers of C. elephantidens are variable in color, protandric, herkogamous and nectarless. Estimators of the breeding system indicated xenogamy, which is consistent with the obligate outcrossing revealed by the pollination experiment. Thirty-seven percent of the plants have female flowers that do not produce pollen, making this population functionally gynodioecious. Both fruit and seed set were high compared to other globose cacti. Pollinators included eight species of native bees, a more diverse pollinator assemblage than other globose cacti. Given the high pressure on pollen due to functional gynodioecy, nectarless flowers, an outcrossing mating system, and the necessity of pollinators to set seeds, we concluded that native bees are highly efficient pollinators that play a crucial role in the sexual reproduction of C. elephantidens.     

铃铛子和赛莨菪（茄科）的传粉机制比较研究

通过野外交配系统试验和传粉昆虫观察,以铃铛子（Anisodus luridus）和赛莨菪（A．camiolicoides）为研究对象,探讨了山莨菪属内自交亲和系统的进化与传粉昆虫的转变。结果表明,铃铛子和赛莨菪均属于自交完全亲和的类群,但两个种的自动自交能力均不强,而且都存在传粉限制。北方黄胡蜂（Vespula rtfarufa）和石长黄胡蜂（Dolichovespula saxonica）分别是铃铛子和赛莨菪的主要传粉昆虫,自然状态下两种昆虫的传粉效率均比较高,但两种昆虫访问两种植物时传递花粉的方式不同,其中北方黄胡蜂主要促进了铃铛子的花间传粉,而石长黄胡蜂访花引起赛莨菪同一朵花内的传粉。通过与该属的另一种植物山莨菪（A．tanguticus）的传粉机制比较,发现在山莨菪属的物种分化过程中,由自交不亲和转变为自交完全亲和,传粉昆虫也发生了转变,证明了自交亲和系统存在于起源较晚的类群中。高山环境中频繁且不可预测的降雨可能降低了传粉昆虫的活动能力,进而导致铃铛子和赛莨菪均存在传粉限制。     

A generalized pollination system in the tropics: bats, birds and Aphelandra acanthus

Background and Aims

A number of different types of flower-visiting animals coexist in any given habitat. What evolutionary and ecological factors influence the subset of these that a given plant relies on for its pollination? Addressing this question requires a mechanistic understanding of the importance of different potential pollinators in terms of visitation rate (pollinator ‘quantity’) and effectiveness at transferring pollen (pollinator ‘quality’) is required. While bat-pollinated plants typically are highly specialized to bats, there are some instances of bat-pollinated plants that use other pollinators as well. These generalized exceptions tend to occur in habitats where bat ‘quantity’ is poor due to low or fluctuating bat densities.

Methods

Aphelandra acanthus occurs in tropical cloud forests with relatively high densities of bat visitors, yet displays a mix of floral syndrome characteristics, suggesting adaptation to multiple types of pollinators. To understand its pollination system better, aspects of its floral phenology and the ‘quantity’ and ‘quality’ components of pollination by its floral visitors are studied here.

Key Results

Flowers were found to open and senesce throughout the day and night, although anther dehiscence was restricted to the late afternoon and night. Videotaping reveals that flowers are visited nocturnally by bats and moths, and diurnally by hummingbirds. Analysis of pollen deposition shows that bats regularly transfer large amounts of conspecific pollen, while hummingbirds occasionally transfer some pollen, and moths rarely do so.

Conclusions

Hummingbirds and bats were comparable in terms of pollination ‘quantity’, while bats were the most effective in terms of ‘quality’. Considering these components together, bats are responsible for approx. 70 % of A. acanthus pollination. However, bats also transferred remarkably large amounts of foreign pollen along with the conspecific grains (three of four grains were foreign). It is suggested that the negative effects of interspecific pollen transfer may decrease bat ‘quality’ for A. acanthus, and thus select for generalization on multiple pollinators instead of specialization on bats.Key words: Specialization, generalization, pollinator effectiveness, hummingbirds, floral syndrome, bat pollination, chiropterophily, ornithophily, cloud forest, heterospecific pollen transfer     

Additional notes on the floral biology of neotropical Lecythidaceae

Observations on the floral biology of seven species of New World Lecythidaceae, including the first report of bat pollination for neotropical members of the family, are presented. The shift from actinomorphic flowers with many stamens to zygomorphic flowers with fewer stamens and the concomitant change from pollen to nectar as the pollinator reward are discussed and related to the respective pollinators. Several mechanisms which operate to reduce competition for pollinators between sympatric species of the family are suggested.