African sunbirds hover to pollinate an invasive hummingbird-pollinated plant

Why do hummingbirds hover while Old World nectar‐feeding birds perch? A unique opportunity to explore this question is presented by the invasion into Africa of a plant adapted for pollination by hovering hummingbirds. Like other hover‐pollinated plants of the New World, the flowers of the tree tobacco Nicotiana glauca lack perches and are oriented towards open space. We find that Old World nectarivores, especially the malachite sunbird, Nectarinia famosa, hover 80% of the time when taking nectar from these flowers. They hover for up to 30 s, and are able to sustain this hovering lifestyle in an area where native nectar plants are absent. Nicotiana glauca greatly increases the local abundance of sunbirds compared with uninvaded areas. In turn, flowers visited by sunbirds formed significantly more capsules and set significantly more seed than sunbird‐excluded flowers, possibly facilitating the invasion. The results suggest a prominent role for plant, rather than bird traits in determining the occurrence of hover‐pollination, begging the question of why plants adapted for hover pollination do not occur outside the New World.     

Pollination and breeding system of the enigmatic South African parasitic plant Mystropetalon thomii (Mystropetalaceae): rodents welcome,but not needed

• Unrelated plants adapted to particular pollinator types tend to exhibit convergent evolution in floral traits. However, inferences about likely pollinators from ‘pollination syndromes’ can be problematic due to trait overlap among some syndromes and unusual floral architecture in some lineages. An example is the rare South African parasitic plant Mystropetalon thomii (Mystropetalaceae), which has highly unusual brush‐like inflorescences that exhibit features of both bird and rodent pollination syndromes.
• We used camera traps to record flower visitors, quantified floral spectral reflectance and nectar and scent production, experimentally determined self‐compatibility and breeding system, and studied pollen dispersal using fluorescent dyes.
• The dark‐red inflorescences are usually monoecious, with female flowers maturing before male flowers, but some inflorescences are purely female (gynoecious). Inflorescences were visited intensively by several rodent species that carried large pollen loads, while visits by birds were extremely rare. Rodents prefer male‐ over female‐phase inflorescences, likely because of the male flowers’ higher nectar and scent production. The floral scent contains several compounds known to attract rodents. Despite the obvious pollen transfer by rodents, we found that flowers on both monoecious and gynoecious inflorescences readily set seed in the absence of rodents and even when all flower visitors are excluded.
• Our findings suggest that seed production occurs at least partially through apomixis and that M. thomii is not ecologically dependent on its rodent pollinators. Our study adds another species and family to the growing list of rodent‐pollinated plants, thus contributing to our understanding of the floral traits associated with pollination by non‐flying mammals.

     

Geographic variation of reproductive traits and competition for pollinators in a bird‐pollinated plant

Geographic variation in the reproductive traits of animal‐pollinated plants can be shaped by spatially variable selection imposed by differences in the local pollination environment. We investigated this process in Babiana ringens (Iridaceae), an enigmatic species from the Western Cape region of South Africa. B. ringens has evolved a specialized perch facilitating cross‐pollination by sunbirds and displays striking geographic variation in perch size and floral traits. Here, we investigate whether this variation can be explained by geographic differences in the pollinator communities. We measured floral and inflorescence traits, and abiotic variables (N, P, C, and rainfall) and made observations of sunbirds in populations spanning the range of B. ringens. In each population, we recorded sunbird species identity and measured visitation rates, interfloral pollen transfer, and whether the seed set of flowers was pollen limited. To evaluate whether competition from co‐occurring sunbird‐pollinated species might reduce visitation, we quantified nectar rewards in B. ringens and of other co‐flowering bird‐pollinated species in local communities in which populations occurred. Variation in abiotic variables was not associated with geographical variation of traits in B. ringens. Malachite sunbirds were the dominant visitor (97% of visits) and populations with larger‐sized traits exhibited higher visitation rates, more between‐flower pollen transfer and set more seed. No sunbirds were observed in four populations, all with smaller‐sized traits. Sunbird visitation to B. ringens was not associated with local sunbird activity in communities, but sunbird visitation was negatively associated with the amount of B. ringens sugar relative to the availability of alternative nectar sources. Our study provides evidence that B. ringens populations with larger floral traits are visited more frequently by sunbirds, and we propose that visitation rates to B. ringens may be influenced, in part, by competition with other sunbird‐pollinated species.     

The Hemipepsis wasp‐pollination system in South Africa: a comparative analysis of trait convergence in a highly specialized plant guild

Pollinator‐mediated convergence in floral traits is the fundamental basis for pollination syndromes, but it has seldom been rigorously analysed. Here we synthesize information on a guild of South African plants that are pollinated by functionally similar pompilid wasps in the genus Hemipepsis and investigate the extent of trait convergence in guild members. The guild includes members from three plant families (Apocynaceae, Orchidaceae and Asparagaceae subfamily Scilloideae) and contains remarkably high levels of functional specialization with 18 of the 23 known guild members being pollinated exclusively by Hemipepsis wasps. The distribution of the guild is centred in the moist upland grasslands of eastern South Africa. Qualitative similarities among guild members include dull greenish‐ or brownish‐white flowers, often with purple blotches, mid‐summer flowering, sweet spicy scent and exposed nectar. To assess the extent of convergent evolution within the guild, we compared floral traits of guild members with those of congeneric non‐wasp‐pollinated species. Guild members typically produce moderate volumes (> 4 µL per flower per day) of concentrated (> 50% sugar by weight) sucrose‐dominant nectar. The nectar properties of guild members did not, however, differ significantly from those of congeneric species pollinated by other vectors. Non‐metric multidimensional scaling of scent data for 15 guild members and 17 congeners (obtained through gas chromatography–mass spectrometry of headspace samples and supplemented with published data) yielded little evidence for convergent evolution in the overall scent composition of guild members. However, convergence in floral spectral reflectance was evident in the guild members; in particular, loci for colours of guild members were significantly closer to the guild centroid than loci for colours of congeners, and they formed a distinct cluster in the blue to blue–green region of the hymenopteran colour hexagon. The colours of guild members were also significantly closer to the colour of background vegetation than those of congeneric species, suggesting a role for cryptic colouring in this system. These results confirm convergence in the floral colours of plants that are pollinated by Hemipepsis spider‐hunting wasps, but also suggest that other traits, such as nectar properties, do not necessarily evolve during shifts between pollination systems. Identification of particular scent compounds and non‐sugar nectar constituents that influence wasp behaviour will be essential for illuminating the extent of biochemical convergence in the guild members. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 278–299.     

Reproductive biology of the Red List species Polemonium caeruleum (Polemoniaceae)

The majority of flowering plants, including many rare and threatened species, are pollinated by animals, but little is known of pollination and breeding systems of many endangered species. Polemonium caeruleum (Polemoniaceae) is a red‐listed species and is regarded as dichogamous, self‐compatible and bee pollinated. However, some studies show that it is visited by a vast assemblage of anthophilous insects from many taxonomic orders and that breeding systems vary greatly between closely related taxa of this genus. Over a period of 3 years we investigated breeding system, dichogamy, nectar secretion and composition, insect visitations and pollen loads in flowers of P. caeruleum in north‐eastern Poland to determine whether the reproductive biology of the plant explains its rarity. Contrary to published data, our study plants were self‐incompatible and showed a high degree of outcrossing. Our experimental work confirmed the occurrence of protandry in this species, revealed that nectar is sucrose‐dominant and proline‐rich and, for the first time for Polemoniaceae, that nectar secretion and nectar sugar concentration in flowers of P. caeruleum is female‐biased. Although flowers were visited by at least 39 species of insects from five taxonomic orders, overall the plant exhibited many characters associated with bee pollination, and analysis of insect performance showed that bumblebees and honeybees are the key pollinators; occasionally hoverflies and butterflies may also be involved. We conclude that, in terms of pollination system, P. caeruleum demonstrates high apparent generalization, but low realized generalization, and is a functional specialist, as most pollinators belong to a single functional group (guild). Its conservation status, at least in our study population, cannot be explained in terms of the biological properties of its breeding or pollination systems; rather, the present decline of the species is caused by habitat loss. However, if this process and bumblebee decline in Europe continue, P. caeruleum populations may diminish in numbers and density and, owing to the self‐incompatibility of the species, quickly become severely pollen‐limited, thereby accelerating further local extinctions. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 92–107.     

Can short‐billed nectar thieving sunbirds replace long‐billed sunbird pollinators in transformed landscapes?

• Pollinator specialisation through exploitation barriers (such as long floral tubes) does not necessarily mean a lack of pollination when the favoured pollinator is rare or absent. Theory predicts that suboptimal visitors will contribute to plant reproduction in the absence of the most effective pollinator. Here I address these questions with Chasmanthe floribunda a long‐tubed plant species in the Cape Floristic Region, which is reliant on one species of pollinator, the long‐billed Malachite Sunbird. In contrast to short‐billed sunbirds, the Malachite Sunbird occurs in lower abundance or is absent in transformed landscapes. Short‐billed sunbirds rob and thieve nectar from long‐tubed flowers, but their potential contribution towards pollination is unknown.
• Experiments assessing seed set after single flower visits were performed to determine whether thieving short‐billed sunbirds can act as substitute pollinators. To determine whether short‐billed sunbirds reduce pollen limitation in transformed areas, pollen supplementation was done by hand and compared to natural fruit set.
• Short billed sunbirds are unable to act as substitute pollinators, and seed set is significantly lower in the flowers that they visited, compared to flowers visited by long‐billed sunbirds. This is substantiated on a landscape scale, where fruit production in Chasmanthe floribunda could artificially be increased by 35% in transformed landscapes, but not so in natural areas.
• These findings have important consequences for the management and conservation of long‐tubed bird‐pollinated plant species that exist in recently transformed landscapes. The potential vulnerability of specialised plant species in transformed landscapes is highlighted.

     

Bird pollination in South African species ofSatyrium (Orchidaceae)

Field observations showed that three South African orchid species,Satyrium carneum, S. coriifolium andS. princeps, are pollinated by sunbirds. Foraging sunbirds insert their bills into the labellum chamber of the flowers and suck nectar from the labellum spurs with their tongues. The column overarches the entrance to the labellum and pollinaria become affixed to the upper mandible of the bill. Birds often attempt to remove pollinaria by rubbing their bills against a branch, but are mostly unsuccessful due to the large plate-like viscidia which attach the pollinaria very firmly to the bill. Other modifications for bird pollination in theseSatyrium species may include the red, carmine or orange colour of the flowers, sturdy inflorescence stems used for perching and large amounts of dilute nectar in the spurs. EachSatyrium species was pollinated by several species of sunbird, and despite some differences in flowering time, occasional hybrids occur at a site whereS. carneum andS. coriifolium share the same sunbird pollinators.     

Is the timing of scent emission correlated with insect visitor activity and pollination in long‐spurred Satyrium species?

Plants are expected to emit floral scent when their pollinators are most active. In the case of long‐tubed flowers specialised for pollination by crepuscular or nocturnal moths, scent emissions would be expected to peak during dawn. Although this classic idea has existed for decades, it has rarely been tested quantitatively. We investigated the timing of flower visitation, pollination and floral scent emissions in six long‐spurred Satyrium species (Orchidaceae). We observed multiple evening visits by pollinaria‐bearing moths on flowers of all study species, but rarely any diurnal visits. The assemblages of moth pollinators differed among Satyrium species, even those that co‐flowered, and the lengths of moth tongues and floral nectar spurs were strongly correlated, suggesting that the available moth pollinator fauna is partitioned by floral traits. Pollinarium removal occurred more frequently during the night than during the day in four of the six species. Scent emission, however, was only significantly higher at dusk than midday in two species. Analysis of floral volatiles using gas chromatography coupled with mass spectrometry yielded 168 scent compounds, of which 112 were species‐specific. The scent blends emitted by each species occupy discrete clusters in two‐dimensional phenotype space, based on multivariate analysis. We conclude that these long‐spurred Satyrium species are ecologically specialised for moth pollination, yet the timing of their scent emission is not closely correlated with moth pollination activity. Scent composition was also more variable than expected from a group of closely related plants sharing the same pollinator functional group. These findings reveal a need for greater understanding of mechanisms of scent production and their constraints, as well as the underlying reasons for divergent scent chemistry among closely related plants.     

Pollination and fruit‐set of Grevillea robusta in western Kenya

The floral visitors of silky oak, Grevillea robusta A. Cunn. ex R.Br., their foraging behaviour and their effects on fruit‐set were studied at Malava, western Kenya. Grevillea robusta is a popular tree for farm plantings in the eastern and central African highlands. Yield of seed has been disappointingly low in some areas and a lack of appropriate pollinators has been suggested as a possible cause. Investigations involved the monitoring of visitors on active inflorescences, assessment of the rewards available to potential pollinators, and exclusion experiments to establish the effects of various visitors on fruit‐set. The flowers are visited mainly by birds and insects. The likely pollinators of G. robusta are sunbirds (Nectarinia amethystina, N. cyanolaema, N. olivacea, N. superba and N. venusta) and white‐eyes (Zosterops kikuyuensis and Z. senegalensis). Very little aggressive behaviour between birds was recorded. No nocturnal pollinators were observed. Nectar was the major floral reward for pollinators, but is likely depleted by ants and honey bees, the foraging behaviour of which confirmed them to be nectar‐robbers. These insects hardly ever touched stigmas during their visits. Eighty‐nine per cent of bird visits were in the morning (07.00–10.00 hours) when nectar volume was highest. Inflorescences bagged to exclude birds set no fruits, and unmanipulated flowers and flowers bagged with self‐pollen set no fruits, indicating a self‐incompatibility mechanism. Control cross‐pollinated flowers displayed greatly increased fruit‐set (25.1%) compared with natural open‐pollination (0.9%). All these findings confirm the importance of cross‐pollen transfer to flowers and the necessity of pollinators for fruit‐set. Effective seed production requires activity of pollinators for self‐pollen removal and cross‐pollen deposition. Seed production stands for G. robusta should be established where flowering is prolific and bird pollinators are abundant.     

Sunbird hovering behavior is determined by both the forager and resource plant

The long‐standing paradigm that pollination systems adapted to hovering birds evolved only in the New World was recently challenged by the discovery of hovering pollination by Old World specialized passerine pollinators. This raises the possibility that hovering pollination may evolve more easily than previously believed, given sufficient selective pressure on plant traits, on nectarivory, or both. We observed foraging behavior by the sunbird Cyanomitra oritis at flowers of the native Old World plant Impatiens sakeriana. We measured the length of pedicels and peduncles (PedPed length), which can make the flowers difficult to reach while the bird perches on the stem, and determined if it influenced sunbird hovering or perching at a flower. Detailed analyses of video recordings showed that sunbirds only hovered at flowers with a long PedPed, whereas they employed both foraging modes when an adequate perch was available. A hovering sunbird could deplete nectar in a shorter time than a perching one. The frequency of visits was not greater at flowers with longer PedPed or with more open I. sakeriana flowers in the vicinity. Our study provides evidence that sunbird behavior does not follow simple energetic models, and that some sunbird pollination systems in the Old World resemble highly specialized hummingbird systems in the New World much more than expected, especially the overall adaptation of the system to bird hovering.     

Flower visitation by birds in Europe

Most flowering plants depend on animal pollination. Several animal groups, including many birds, have specialized in exploiting floral nectar, while simultaneously pollinating the flowers they visit. These specialized pollinators are present in all continents except Europe and Antarctica, and thus, insects are often considered the only ecologically relevant pollinators in Europe. Nevertheless, generalist birds are also known to visit flowers, and several reports of flower visitation by birds in this continent prompted us to review available information in order to estimate its prevalence. We retrieved reports of flower–bird interactions from 62 publications. Forty‐six bird species visited the flowers of 95 plant species, 26 of these being exotic to Europe, yielding a total of 243 specific interactions. The ecological importance of bird–flower visitation in Europe is still unknown, particularly in terms of plant reproductive output, but effective pollination has been confirmed for several native and exotic plant species. We suggest nectar and pollen to be important food resources for several bird species, especially tits Cyanistes and Sylvia and Phylloscopus warblers during winter and spring. The prevalence of bird flower‐visitation, and thus potential bird pollination, is slightly more common in the Mediterranean basin, which is a stopover to many migrant bird species, which might actually increase their effectiveness as pollinators by promoting long‐distance pollen flow. We argue that research on bird pollination in Europe deserves further attention to explore its ecological and evolutionary relevance.     

Morphological and physiological divergences within Quercus ilex support the existence of different ecotypes depending on climatic dryness

Background and Aims

According to the Grant–Stebbins model of pollinator-driven divergence, plants that disperse beyond the range of their specialized pollinator may adapt to a new pollination system. Although this model provides a compelling explanation for pollination ecotype formation, few studies have directly tested its validity in nature. Here we investigate the distribution and pollination biology of several subspecies of the shrub Erica plukenetii from the Cape Floristic Region in South Africa. We analyse these data in a phylogenetic context and combine these results with information on pollinator ranges to test whether the evolution of pollination ecotypes is consistent with the Grant–Stebbins model.

Methods and Key Results

Pollinator observations showed that the most common form of E. plukenetii with intermediate corolla length is pollinated by short-billed Orange-breasted sunbirds. Populations at the northern fringe of the distribution are characterized by long corollas, and are mainly pollinated by long-billed Malachite sunbirds. A population with short corollas in the centre of the range was mainly pollinated by insects, particularly short-tongued noctuid moths. Bird exclusion in this population did not have an effect on fruit set, while insect exclusion reduced fruit set. An analysis of floral scent across the range, using coupled gas chromatography–mass spectrometry, showed that the scent bouquets of flowers from moth-pollinated populations are characterized by a larger number of scent compounds and higher emission rates than those in bird-pollinated populations. This was also reflected in clear separation of moth- and bird-pollinated populations in a two-dimensional phenotype space based on non-metric multidimensional scaling analysis of scent data. Phylogenetic analyses of chloroplast and nuclear DNA sequences strongly supported monophyly of E. plukenetii, but not of all the subspecies. Reconstruction of ancestral character states suggests two shifts from traits associated with short-billed Orange-breasted sunbird pollination: one towards traits associated with moth pollination, and one towards traits associated with pollination by long-billed Malachite sunbirds. The latter shift coincided with the colonization of Namaqualand in which Orange-breasted sunbirds are absent.

Conclusions Erica plukenetii

is characterized by three pollination ecotypes, but only the evolutionary transition from short- to long-billed sunbird pollination can be clearly explained by the Grant–Stebbins model. Corolla length is a key character for both ecotype transitions, while floral scent emission was important for the transition from bird to moth pollination.     

Visual signalling of nectar‐offering flowers and specific morphological traits favour robust bee pollinators in the mass‐flowering tree Handroanthus impetiginosus (Bignoniaceae)

Mass flowering is a widespread blooming strategy among Neotropical trees that has been frequently suggested to increase geitonogamous pollination. We investigated the pollination ecology of the mass‐flowering tree Handroanthus impetiginosus, addressing its breeding system, the role in pollination of different visitors, the impact of nectar robbers on fruit set and the function of colour changes in nectar guides. This xenogamous species is mainly pollinated by Centris and Euglossa bees (Apidae) seeking nectar, which are known to fly long distances. The flowers favour these bees by having: (1) a closed entrance in newly opened flowers which provides access only to strong bees capable of deforming the flower tube; and (2) a nectar chamber that is accessible only to long‐tongued bees. Only first‐day flowers with yellow nectar guides produce nectar. Pollinators prefer these flowers over second‐ and third‐day flowers with orange and red nectar guides, respectively. Nectar robbers damage two‐thirds of the flowers and this robbing activity decreases fruit set by half. We attribute the low fruit set of H. impetiginosus to the intense nectar robbing and hypothesize that visual signalling of nectar presence in newly opened (receptive) flowers reduces geitonogamy by minimizing bee visits to unrewarding (non‐receptive) flowers. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 396–407.     

Food selection by avian floral visitors: an important aspect of plant–flower visitor interactions in West Africa

Community‐level studies have shown that plant–pollinator interactions are much more generalized than previously expected. Consequently, many authors have questioned the significance of phenotypic complementarity between plants and pollinators and abundance effects in pollination interactions. Here, we compare the behaviour of three sunbird species feeding on the nectar of five plant species in afromontane vegetation. We studied the feeding behaviour with and without consideration of plant abundance (i.e. diet selectivity and diet composition, respectively). The aims of the study were to estimate: (1) how relative resource abundance influences flower selectivity; (2) the degree of phenotypic matching; and (3) whether different plant resource assessment methods give different answers to this question. The results showed that, although sunbirds frequently feed on both morphologically adapted and nonadapted plants, food selectivity data are consistent with the hypothesis of phenotypic complementarity. Moreover, we found that the type of plant abundance measurement can change conclusions in some cases, as individual plants differ in their growth habits and nectar production. This effect was most obvious for the assessment of selectivity of the northern double‐collared sunbird (Cinnyris reichenowi) and for Hypoestes aristata, a plant producing inflorescences composed of a large number of small flowers possessing small amounts of nectar per flower (a high abundance of flowers, but a low abundance of nectar relative to the remaining plant community). © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Pollination ecology of the pre-Pyrenean endemic Petrocoptis montsicciana (Caryophyllaceae): effects of population size

Petrocoptis montsicciana (Caryophyllaceae) is a threatened pre‐Pyrenean endemic that grows exclusively on caves and walls of limestone. We studied its pollination ecology by monitoring phenology and by evaluating pollen and nectar production, pollinator activity (frequency and behaviour of visitors), quantity and quality of pollination services, pollen/ovule ratio, and seed set in response to insect exclusion and self‐compatibility tests. We also analysed the effect of population size on reproductive mechanisms by comparing a large and a small population. Flowers of P. montsicciana produced nectar and were visited by Hymenoptera (79.7%), Diptera (11.5%), and Lepidoptera (8.8%). The most frequent pollinators (60.6% of total visits) were long‐tongued bees of the genus Anthophora. Both populations had a similar range of pollinators. We found a correlation between the number of visited flowers and the number of open flowers per census; 88.7% of pollen grains deposited on the stigmas were conspecific and the main competitor was another chasmophyte plant, Antirrhinum molle. Bagged flowers set seeds but significantly less so than hand‐self‐pollinated and control flowers. Thus, although self‐compatible and self‐pollinated, entomophilous pollination of P. montsicciana is required in order to explain c. 10–40% of total seed set, in accordance with P/O ratio estimations. Bagged flowers from the small population set significantly more seeds than the large one. Visitation rates were lower in the small population, but, unexpectedly, showed higher stigmatic pollen loads and similar or higher seed set. These results suggest an increase of spontaneous selfing rates in the small population, probably favoured by a smaller flower size, which can not only assure reproductive success when pollinators are scarce, but also provide additional potential to adapt to climatic changes. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76 , 79–90.     

Specialized pollination in the African milkweed Xysmalobium orbiculare: a key role for floral scent in the attraction of spider-hunting wasps

Specialized pollination by prey-hunting wasps is poorly documented in rewarding plants. Furthermore, the mechanisms of achieving specialization are not clear since flowers typically produce exposed nectar and have no morphological adaptations (such as long spurs) to exclude non-pollinating visitors. We investigated the pollination of Xysmalobium orbiculare and explored the functional roles of floral scent and nectar in attracting pollinators and deterring nectar robbers. Floral visitor observations showed that this milkweed is visited almost exclusively by pompilid wasps in the genus Hemipepsis. These wasps were the only insects to carry pollinia, and a cage experiment confirmed their effectiveness in removing and inserting pollinia on flowers. Hand-pollinations showed that plants are genetically self-incompatible and thus reliant on pollinators for seed set. Palatability experiments with honeybees showed that nectar is distasteful to non-pollinating insects and is therefore likely to play a functional role in deterring nectar thieves. Choice experiments in the field showed that the wasp pollinators are attracted primarily by floral scent rather than visual cues. Analysis of spectral reflectance of flowers revealed that flowers are dull colored and are unlikely to stand out from the background vegetation. We conclude that X. orbiculare is specialized for pollination by spider-hunting wasps in the genus Hemipepsis and utilizes floral scent to selectively attract its pollinators and unpalatable nectar to deter non-pollinating visitors.     

Hovering sunbirds in the Old World: occasional behaviour or evolutionary trend?

The nectarivory of sunbirds in the Old World and hummingbirds in the New World evolved independently. While both groups are specialised in their feeding apparatuses, hummingbirds are moreover famous for their adaptations to sustained hovering flight. Recently, an example of a pollination system of the invasive plant Nicotiana glauca has been used to show that less adapted sunbirds also are frequently able to hover. Nevertheless, the question has remained why plants adapted to bird hovering pollination do not occur outside the New World. In this paper we show that the long‐peduncle Cameroonian Impatiens sakeriana is not capable of autonomous selfing and can be pollinated only by two often hovering sunbirds, the Cameroon sunbird Cyanomitra oritis and the northern double‐collared sunbird Cinnyris reichenowi. Our study revealed that this plant is highly specialised for pollination by C. oritis. Cinnyris reichenowi hovers less frequently and often thieves nectar by piercing the flower spur when perching. This study shows that pollination systems occurring in the Old World follow similar evolutionary trends as systems including hovering hummingbirds in the New World.     

Nectar sugar composition of European Caryophylloideae (Caryophyllaceae) in relation to flower length,pollination biology and phylogeny

Floral nectar composition has been explained as an adaptation to factors that are either directly or indirectly related to pollinator attraction. However, it is often unclear whether the sugar composition is a direct adaptation to pollinator preferences. Firstly, the lower osmolality of sucrose solutions means that they evaporate more rapidly than hexose solutions, which might be one reason why sucrose‐rich nectar is typically found in flowers with long tubes (adapted to long‐tongued pollinators), where it is better protected from evaporation than in open or short‐tubed flowers. Secondly, it can be assumed that temperature‐dependent evaporation is generally lower during the night than during the day so that selection pressure to secrete nectar with high osmolality (i.e. hexose‐rich solutions) is relaxed for night‐active flowers pollinated at night. Thirdly, the breeding system may affect selection pressure on nectar traits; that is, for pollinator‐independent, self‐pollinated plants, a lower selective pressure on nectar traits can be assumed, leading to a higher variability of nectar sugar composition independent of pollinator preferences, nectar accessibility and nectar protection. To analyse the relations between flower tube length, day vs. night pollination and self‐pollination, the nectar sugar composition was investigated in 78 European Caryophylloideae (Caryophyllaceae) with different pollination modes (diurnal, nocturnal, self‐pollination) using high‐performance liquid chromatography (HPLC). All Caryophylleae species (Dianthus and relatives) were found to have nectar with more than 50% sucrose, whereas the sugar composition of Sileneae species (Silene and relatives) ranged from 0% to 98.2%. In the genus Silene, a clear dichotomous distribution of sucrose‐ and hexose‐dominant nectars is evident. We found a positive correlation between the flower tube length and sucrose content in Caryophylloideae, particularly in day‐flowering species, using both conventional analyses and phylogenetically independent contrasts.     

Comparison of floral traits and pollinator assemblages of insular and mainland varieties of Lilium auratum

Lilium auratum var. platyphyllum, which is endemic to the Izu Islands, has white petals and emits a strong floral scent, typical of moth‐pollinated plants. Moths might be important pollinators within the Izu Islands because swallowtail butterflies are absent or rare there. Therefore, we investigated insular var. platyphyllum and widespread L. auratum var. auratum on the mainland of Japan to clarify the relationship between floral characteristics and pollinators. Measurement of floral scent intensity using an odor sensor indicated that the intensity increased in the evening and at night in var. platyphyllum, whereas intensity increased at night in var. auratum. Total sugar weight in nectar, which was calculated by nectar volume and sugar concentration, showed that the flowers of var. platyphyllum secreted nectar abundantly both in the evening and at night, whereas those of var. auratum secreted an almost constant amount of nectar throughout the day. Flower visitor assemblages and their frequencies studied using digital cameras suggested that crepuscular and nocturnal hawkmoths are important pollinators for var. platyphyllum. In contrast, both diurnal swallowtail butterflies and nocturnal large hawkmoths are important and effective pollinators for var. auratum. These conclusions were also supported by the exclusion experiments of either diurnal or nocturnal flower visitors using mesh bags. The rates of seed sets of var. platyphyllum were significantly higher from nocturnal pollination than from diurnal pollination. Thus, this study revealed that floral traits of var. platyphyllum show more adaptation for crepuscular and nocturnal hawkmoths, which are relatively abundant in the Izu Islands, than those of var. auratum.     

Termites and the turnover of dead wood in an arid tropical environment

Summary The role of sunbirds (Nectariniidae) in the pollination ecology of Strelitzia nicolai (Musaceae) was studied for one year in a coastal dune forest in Zululand, South Africa. It was found that S. nicolai produced large quantities of low quality nectar (1.74 j/l); that nectar production was highest during the day-time; and that the flowers displayed several characteristics attractive to bird-visitors. The flowers were large, conspicuous and provided the birds with a perch, facilitating easy access to the nectar. Flowers were visited by four species of sunbirds: Olive Sunbird Nectarinia olivacea, Grey Sunbird N. veroxii, Black Sunbird N. amethystina, and Collared Sunbird Anthreptes collaris. Sunbirds visited the flowers throughout the year, and apparently cued into changes in the flower angle as an indication of nectar flow rates. Sunbirds perched on the flowers in a manner which effected pollination, the pollen being transferred to the stigma via the birds' feet. Besides the sunbirds, there were other visitors (bushbabies, monkeys and insects) to the flowers, but they did not visit the flowers frequently nor did they appear to be significant pollinators. The high seed set of S. nicolai in the study area attests to the efficacy of the sunbirds as pollinators.