Honeyeaters and the New Zealand forest flora: The utilisation and profitability of small flowers

New Zealand flowers are frequently considered unspecialised allowing easy access to pollen and nectar by a wide range of visitors. Most conform with a syndrome of insect pollination (entomophily). Pollination of forest flowers by birds has been described for a range of species whose flowers are morphologically ornithophilous. On Kapiti Island and Little Barrier Island, all three species of New Zealand honeyeaters have been described feeding on flowers currently assumed to be entomophilous or where the pollination system is unknown. The persistence and regularity of visits suggests that the birds are obtaining suitable rewards in the form of nectar and could be serving as pollinators. We measured the nectar energetic value from flowers of three ornithophilous and five entomophilous species. Nectar production over 24 hours was highest in ornithophilous species, but the standing crop of nectar overlapped—ornithophilous species: Metrosideros fulgens (standing crop 6.6 J), Metrosideros excelsa (22 J), and Fuchsia excorticata (1.8 J); and entomophilous: Pittosporum crassifolium (23 J), Pseudopanax arboreus (1.5 J), Dysoxylum spectabile (3.7 early flowers -6.7 J late flowers), Pittosporum eugenioides (2.7 J) and Geniostoma rupestre (1.8 J). The entomophilous species present the flowers in aggregation and as result birds can visit a large number flowers per minute. We found that the average estimated nectar consumption rate for all the entomophilous species except G. rupestre was enough to sustain the two smaller New Zealand honeyeaters (hihi energy requirements= 0.12 kJ min(-1), median energy obtained: 0.16 kJ min(-1) D. spectabile—0.57 kJ min(-1) P. crassifolium); bellbird energy requirements = 0.10 kJ min(-1), median energy obtained: 0.14 kJ min(-1) D. spectabile—0.68 kJ min(-1) P. crassifolium). However, we estimate that if the birds are able to selectively forage on the flowers with most nectar, the energetic returns of all species may be sufficient for hihi and bellbird (hihi: 0.18 kJ min(-1) G. rupestre—0.93 kJ min(-1); P. crassifolium; bellbird: 0.12 kJ min(-1) G. rupestre 1.11 kJ min(-1) P. crassifolium). If tui (energy requirements: 0.25 kJ min(-1), forages randomly, only P. crassifolium (0.80 kJ min(- 1)) and D. spectabile late in the season (0.30 kJ min(-1)) provide sufficient returns, but if selective, P. arboreus (0.45 kJ min(-1)) may also suffice. We suggest that because (a) the nectar produced by entomophilous flowers provides sufficient energy to sustain the energetic requirements of birds, and (b) these plants flower in the cooler months when insect activity is reduced, birds might have played a wider role in pollination than previously considered. This finding is of particular importance because the abundance of New Zealand honeyeaters on the mainland has decreased considerably since human colonisation and this could be affecting forest regeneration.     

Effectiveness of short‐tongued bees as pollinators of apparently ornithophilous New Zealand mistletoes

Abstract The flowers of two species of threatened New Zealand mistletoes (Peraxilla tetrapetala and Peraxilla colensoi, Loranthaceae) have explosive buds that do not open unless force is applied by birds or two species of native short‐tongued bees. Opened flowers are visited by a variety of birds and insects. Although both species of Peraxilla conform to a pollination syndrome of ornithophily, bees may be effective alternative pollinators. We investigated the effectiveness of bees and birds as pollinators of P. colensoi at one site and P. tetrapetala at two sites in the South Island. Bees and other insects outnumbered birds as flower visitors at all three sites. By excluding birds with wire cages, we showed that two bee species regularly open flowers of P. tetrapetala, but only rarely open flowers of P. colensoi. Few pollen grains were deposited when either birds or bees opened buds, so opening buds was not by itself sufficient for adequate pollination. Instead, pollen continued to accumulate over the next 6 or 7 days, even inside cages that excluded birds. Both populations of P. tetrapetala were regularly pollen‐limited, but in different ways. At Ohau, opened flowers gained enough pollen to produce seeds, but many buds were not opened and hence failed to set seed. In contrast, at Craigieburn, nearly all buds were opened, but many of these did not receive enough pollen. These results demonstrate that native bees can partially replace birds as pollinators of mistletoes, despite their apparent ornithophilous syndrome. Ongoing reductions in New Zealand forest bird numbers means that the service bees provide may be important for the long‐term future of these plants.     

Intra‐floral resource partitioning between endemic and invasive flower visitors: consequences for pollinator effectiveness

1. Sympatric flower visitor species often partition nectar and pollen and thus affect each other's foraging pattern. Consequently, their pollination service may also be influenced by the presence of other flower visiting species. Ants are solely interested in nectar and frequent flower visitors of some plant species but usually provide no pollination service. Obligate flower visitors such as bees depend on both nectar and pollen and are often more effective pollinators. 2. In Hawaii, we studied the complex interactions between flowers of the endemic tree Metrosideros polymorpha (Myrtaceae) and both, endemic and introduced flower‐visiting insects. The former main‐pollinators of M. polymorpha were birds, which, however, became rare. We evaluated the pollinator effectiveness of endemic and invasive bees and whether it is affected by the type of resource collected and the presence of ants on flowers. 3. Ants were dominant nectar‐consumers that mostly depleted the nectar of visited inflorescences. Accordingly, the visitation frequency, duration, and consequently the pollinator effectiveness of nectar‐foraging honeybees (Apis mellifera) strongly decreased on ant‐visited flowers, whereas pollen‐collecting bees remained largely unaffected by ants. Overall, endemic bees (Hylaeus spp.) were ineffective pollinators. 4. The average net effect of ants on pollination of M. polymorpha was neutral, corresponding to a similar fruit set of ant‐visited and ant‐free inflorescences. 5. Our results suggest that invasive social hymenopterans that often have negative impacts on the Hawaiian flora and fauna may occasionally provide neutral (ants) or even beneficial net effects (honeybees), especially in the absence of native birds.     

Severe pollen limitation in populations of the New Zealand shrub Alseuosmia macrophylla (Alseuosmiaceae) can be attributed to the loss of pollinating bird species

The loss of bird species following human colonization of New Zealand has raised concerns about the consequences for crucial ecosystem functions such as pollination. The understorey shrub Alseuosmia macrophylla (Alseuosmiaceae) exhibits characteristics typical of a bird pollination syndrome, but populations still persist in northern North Island forest remnants despite the local extinction of most endemic bird pollinators, leading to the suggestion that moths – rather than birds – may be the primary pollinators. The aim of this study was to quantify the importance of endemic birds as pollinators of A. macrophylla over several years by comparing plants on Little Barrier Island (LBI), where all extant endemic bird pollinators still occur, to plants at sites on the adjacent North Island in the Waitakere Ranges (WTK), where only one of these species remains common. Flowers on LBI were visited by endemic bellbirds (Anthornis melanura) and stitchbirds (Notiomystis cincta), while at WTK sites the most common visitors were the recently arrived silvereye (Zosterops lateralis) and the introduced honeybee (Apis mellifera), both of which acted principally as nectar robbers. Caged flowers on LBI had significantly lower fruit set than open flowers, and plants at WTK were significantly more pollen‐limited than plants on LBI. This provides evidence that the loss of endemic pollinating birds is the most likely reason for the high pollen limitation found in some North Island A. macrophylla populations, and the very low seed set of these populations could have serious implications for the long‐term persistence of this species.     

Integration of alien plants into a native flower-pollinator visitation web

Introduced alien species influence many ecosystem services, including pollination of plants by animals. We extend the scope of recent 'single species' studies by analysing how alien plant species integrate themselves into a native flower visitation web. Historical records for a community in central USA show that 456 plant species received visits from 1429 insect and 1 hummingbird species, yielding 15 265 unique interactions. Aliens comprised 12.3% of all plant species, whereas only a few insects were alien. On average, the flowers of alien plants were visited by significantly fewer animal species than those of native plants. Most of these visitors were generalists, visiting many other plant species. The web of interactions between flowers and visitors was less richly connected for alien plants than for natives; nonetheless, aliens were well integrated into the native web. Because most visitors appear to be pollinators, this integration implies possible competitive and facilitative interactions between native and alien plants, mediated through animal visitors to flowers.     

Relative importance of diurnal and nocturnal pollinators for reproduction in the early spring flowering shrub Stachyurus praecox (Stachyuraceae)

Generalized pollination systems may be favored in early spring flowering plants, as during this period pollinator activity is unpredictable. Many previous studies have concentrated on the importance of diurnal visitors in pollination, and consequently, information on the contribution of nocturnal visitors to pollination in early spring is limited. This study was conducted to evaluate the relative importance of diurnal and nocturnal pollinators in the early spring flowering dioecious shrub Stachyurus praecox (Stachyuraceae), in two temperate forests in central Japan. Visitors to the female and male flowers were observed during day and night, and their relative contributions to seed set were compared. The pollinator observations revealed that the diurnal and nocturnal insects visited both male and female flowers, and that the main flower visitors were diurnal small bees and flies as well as nocturnal settling moths. The diurnal and nocturnal flower visitors also acted as pollinators, as the pollen grains of S. praecox were attached to the insects collected from the female flowers. Pollination experiments demonstrated that the contributions of diurnal pollinators to the seed set were higher than those of the nocturnal pollinators. The results of this study indicate that S. praecox has a generalized pollination system, comprising both diurnal insects and nocturnal settling moths. Although the roles of diurnal insects are more important in the pollination of S. praecox, nocturnal settling moths may have a complementary role in early spring.     

Plant-pollinator interactions in New Caledonia influenced by introduced honey bees

The flora of New Caledonia is characterized by remarkably high species diversity, high endemicity, and an unusual abundance of archaic plant taxa. To investigate community-level pollination mutualism in this endemic ecosystem, we observed flower visitors on 99 plant species in 42 families of various types of vegetation. Among the 95 native plant species, the most dominant pollination system was melittophily (bee-pollinated, 46.3%), followed by phalaenophily (moth-pollinated, 20.0%), ornithophily (bird-pollinated, 11.6%), cantharophily (beetle-pollinated, 8.4%), myophily (fly-pollinated, 3.2%), chiropterophily (bat-pollinated, 3.2%), and anemophily (wind-pollinated, 3.2%). The prevalence of ornithophily by honeyeaters shows an ecological link to pollination mutualism in Australia. The relative dominance of phalaenophily is unique to New Caledonia, and is proposed to be related to the low diversity of the original bee fauna and the absence of long-tongued bees. Although some archaic plants maintain archaic plant-pollinator interactions, e.g., Zygogynum pollinated by micropterigid moths, or Hedycarya pollinated by thrips and staphylinid beetles, the most dominant organism observed on flowers was the introduced honey bee, Apis mellifera. The plant species now visited by honey bees are thought to have originally been pollinated by native solitary short-tongued bees. Our data suggest that the unique systems of pollination mutualism in New Caledonia are now endangered by the establishment of highly invasive honey bees.     

Mutualisms with the wreckage of an avifauna: the status of bird pollination and fruit dispersal in New Zealand

Worldwide declines in bird numbers have recently renewed interest in how well bird?plant mutualisms are functioning. In New Zealand, it has been argued that bird pollination was relatively unimportant and bird pollination failure was unlikely to threaten any New Zealand plants, whereas dispersal mutualisms were widespread and in some cases potentially at risk because of reliance on a single large frugivore, the kereru (Hemiphaga novaeseelandiae). Work since 1989, however, has changed that assessment. Smaller individual fruits of most plant species can be dispersed by mid-sized birds such as tui (Prosthemadera novaezelandiae) because both fruits and birds vary in size within a species. Only one species (Beilschmiedia tarairi) has no individual fruits small enough for this to occur. Germination of 19 fleshy-fruited species, including most species with fruits >8 mm diameter, does not depend on birds removing the fruit pulp. The few studies of fruit removal rates mostly (7 out of 10) show good dispersal quantity. So dispersal is less at risk than once thought. In contrast, there is now evidence for widespread pollen limitation in species with ornithophilous flowers. Tests on 10 of the 29 known native ornithophilous-flowered species found that in 8 cases seed production was reduced by at least one-third, and the pollen limitation indices overall were significantly higher than the global average. Birds also frequently visit flowers of many other smaller-flowered native species, and excluding birds significantly reduced seed set in the three species tested. So pollination is more at risk than once thought. Finally, analyses of both species numbers and total woody basal area show that dependence on bird pollination is unexpectedly high. Birds have been recorded visiting the flowers of 85 native species, representing 5% of the total seed-plant flora (compared with 12% of those with fleshy fruit) and 30% of the tree flora (compared with 59% with fleshy fruit). A higher percentage of New Zealand forest basal area has bird-visited flowers (37% of basal area nationally) than fleshy fruit (31%). Thus, bird pollination is more important in New Zealand than was realised, partly because birds visit many flowers that do not have classic ?ornithophilous? flower morphology.     

Pollinator visits to floral colour phases of Fuchsia excorticata

Abstract

Fuchsia excorticata is a gynodioecious tree (endemic to New Zealand) which is pollinated by honeyeater birds. Red, tubular flowers are common among bird-pollinated plants, and the tubular flowers of F. excorticata change colour from green to red. The purpose of the present study was to describe the timing of the colour change, dropping of the floral tube, and nectar production of F. excorticata and to determine how bellbirds (Anthornis melanura) and two introduced species of nectar robbers (Zosterops lateralis and Bombus sp.) respond to the different colour phases.

Floral tubes fell off about 11 days after anthesis in both sexes, with colour change occurring on about Day-4 for female trees and on about Day-5 for hermaphrodite trees. Green-phase hermaphrodite flowers produced significantly more nectar/day than did green-phase female flowers, while red-phase flowers did not produce nectar in either sex. All three floral visitors studied preferentially visited green-phase flowers and virtually ignored the nectarless flowers in the red phase. These results contrast with the general association between red, bird-pollinated flowers and the presence of a nectar reward. We suggest that the non-migratory habit of the New Zealand honeyeaters and the lack of native insect visitors to this species may account for this anomalous green-to-red colour change.     

Reproductive biology of two Himalayan alpine gingers (Roscoea spp., Zingiberaceae) in China: pollination syndrome and compensatory floral mechanisms

According to the concept of pollination syndromes, floral traits reflect specialisation to a particular pollinator or set of pollinators. However, the reproductive biology of endemic, and often specialised, plants may require increased attention as climate change accelerates worldwide. Species of Roscoea endemic to the Himalayan region have striking orchid-like flowers with long corolla tubes, suggesting pollination by long-tongued insects. Until now, the reproductive biology of species of Roscoea has been poorly documented. We investigated the floral biology, breeding system and pollination ecology of R. cautleoides and R. humeana, from Hengduan Mountains, a global biodiversity hotspot in southwest China. We also tested whether floral longevity increases pollination success. Pollination experiments showed that the two species were self-compatible and depended on insects for fruit production. Over several flowering seasons we did not observe any potential pollinators with long tongues that matched the corolla tube visiting flowers in centres of distribution. The principal pollinators observed were pollen-collecting generalist bees, with low visitation frequencies. In general, members of the ginger family are characterised by short-lived (usually 1 day) flowers, but flowers of R. cautleoides and R. humeana last 8 and 6 days, respectively. Removing stigmas decreased fruit set in both study populations. Our results suggest that the original pollinators may have been long-tongued insects that are now absent from the Chinese Himalayas because habitats have responded to climate change. However, long-lived and self-compatible flowers, coupled with the presence of generalist pollinators, are traits that have allowed these gingers to reproduce and continue to persist in the alpine habitats.     

First confirmation of a native bird-pollinated plant in Europe

The pollination of Anagyris foetida L. (Fabaceae), a Mediterranean species that is a relict of the Tertiary, was studied in two populations of SW Spain over a three-year period. Numerous censuses of birds and insects were carried out, the floral nectar was quantified, and specific tests were performed to determine the pollinators' pollen load, the pollen's effective transfer to the pistil, and spontaneous self-pollination. The most important pollinators were three species of passeriforms – Phylloscopus collybita Vieillot, Sylvia atricapilla L. and S. melanocephala Gmelin– a result coherent with findings in populations of S and E Spain. The negligible existence of insect visitors and pollinators of A. foetida flowers could be explained by the early flowering of this species during the autumn–winter, coinciding with the coolest and wettest months of the year (cold, high winds, almost daily mists that persist until nightfall, and above all, abundant rainfall). The pollen loads carried by the birds were high, as were also the loads transferred to the pistil. The fruit-set of bagged flowers was very low, evidence of the plant's need for the birds as pollinators. This is the first proof of the existence of a native European bird-pollinated plant, since besides its peculaliarities (flowers odourless, pseudotubular, with no landing platform, pendulous, diurnal populations were mainly pollinated by three passeriform species.     

The relative importance of birds and bees in the pollination of Metrosideros excelsa (Myrtaceae)

Exclusion experiments were used to assess the effect of different pollinator groups on outcrossing and seed production in Metrosideros excelsa. The main study site was Little Barrier Island, New Zealand where indigenous bird and native solitary bees are the main flower visitors. Our results showed that native birds were more important pollinators of M. excelsa than native bees. Seed production was much higher in open pollination than in two exclusion experiments where either birds were excluded and native bees only had access to flowers, or where all pollinators had been excluded. The number of fertile seeds per capsule was 45% higher after open pollination than in treatments with bee visitation only and 28% higher than in treatments where all flower visitors were excluded. Estimated outcrossing rates were significantly higher (t_m = 0.71) for open pollination in the upper canopy (>4 m above‐ground level) where bird visitation is presumed to be more frequent than for a treatment with native bee access only (t_m = 0.40). Our results also suggest that a large proportion of seeds (66%) arise from autonomous self‐pollination when all pollinators are excluded. In four trees of a modified mainland population with predominantly introduced birds and a mixture of introduced and native bees there was no decrease in seed production for the treatment allowing bee access only, indicating that – in contrast to native bees – honeybees may be more efficient pollinators of M. excelsa. Observation of the foraging behaviour of both groups of bees showed that native bees contact the stigma of flowers less frequently than honeybees. This is likely to be a consequence of their smaller body size relative to honeybees.     

Intraseasonal variation in pollination intensity and seed set in an alpine population of Ranunculus acris in southwestern Norway

I studied aspects of the pollination and reproduction ecology of an alpine population of the circurnpolar Ranunculus acris (Ranunculaceae) at Hardangervidda, southwest Norway Dipteran families, mainly Muscidae and Anthomyudae, were the most frequent flower visitors and pollinators A single visit by these insects resulted in a seed set of c 18% of the total potential Visitation rates were highest early m the flowering season The longevity of individual flowers of early flowering plants was c 3 d shorter than that of mid-season flowering individuals Insect pollinators moved short distances between flowers and they mostly visited near neighbour plants Expenments showed that Ranunculus acris was self-incompatible and thus dependent on insect visitation for seed production Early flowering individuals had a very high seed set relative to individuals flowering in mid- and late season, suggesting a strong selection pressure for early flowering in the population Seed production in this Ranunculus acris population seems to be limited by severe climatic conditions and a low pollination intensity     

Forest fragments influence pollination and yield of soybean crops in Chaco landscapes

Habitat remnants act as a source of pollinators potentially relevant for crop pollination and yield. This work analyzes how habitat loss influences pollinators, effective pollination and yield of soybean crops. The study area comprises ten sites adjacent to forest patches surrounded by a soybean matrix in central Argentina (eight sites in the season 2014–2015 and two sites in the season 2015–2016). Pollination was estimated by pollen deposition and frequency of flower visitors. Pollen deposition on stigmas and seed set were measured comparing open plants and plants with pollinator exclusion. These response variables were compared considering increasing distance to the forest edge and an increasing gradient of forest patch size. Bees were the most frequent visitors of soybean flowers, especially honeybees, but also at least three native bee species were recorded. Open plants showed higher rates of stigmatic pollen deposition than plants with pollinator exclusion, but seed set was similar. Total insect visitation rates, especially of native insects, decreased with distance to the forest edge and so did pollen deposition. Pollen deposition and seed set increased with increasing forest patch size for plants located near and far from the forest edge, respectively. Overall, our results suggest that the contribution of native pollinators from local forest patches is important for effective pollination across the landscape. Small patches of forest (approximately 1 ha.) guarantee pollinators to ensure plant yields similar to the yields of plants growing close to large patches, but only at short distances; while larger forest patches provide better pollination services for the crop at larger distances from the forest edge. However, we encourage further studies because results suggest that other factors may also influence soybean pollination and production.     

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.     

Flowering phenology,seed set and bird pollination of five Western Australian Banksia species

Flowering phenology and seed set characteristics of five species of Banksia were studied in relation to the nectarivorous birds which feed at their inflorescences. Within the Banksia woodland at the study site near Perth, the flowering seasons of the Banksia species were sequential and only slightly overlapping, providing a year-round nectar source. Although honeyeaters visited alt five species, seed set was very low in each case. Caging experiments indicated that, in B. attenuata at least, alternative pollinators may play a more important role in pollination than do nectar-feeding birds. It is suggested that non-avian pollinators, predatory insects, and characteristics of the breeding system may also have been important in the evolution of the observed flowering phenology and patterns of seed set.     

Reproductive biology of Echinopsis terscheckii (Cactaceae): the role of nocturnal and diurnal pollinators

The aim of this study was to analyse the reproductive biology of Echinopsis terscheckii, a species endemic to northwest Argentina that has nocturnal flowers. We expected that this species had a generalised pollination system, with moths and diurnal visitors as the primary pollinators. To test this, we studied the floral biology, breeding system and floral visitors of this species and the effectiveness of nocturnal and diurnal visitors. Floral biology was defined based on floral morphology, floral cycle and nectar production of the flowers. The breeding system and relative contributions of diurnal and nocturnal visitors to fruit and seed set were analysed through field experiments. E.?terscheckii flowers opened at sunset and closed the following day. The peak of nectar production occurred at midnight. Flowers were determined to be self-incompatible. Moths, bees and birds were identified as floral visitors. Moths were the most frequent visitors at night, whereas bees were the most frequent visitors during the day. Fruit production by diurnal pollinators was less than that by nocturnal pollinators; among all floral visitors, moths were the most effective pollinators. We have demonstrated for the first time that moths are the primary pollinators of columnar cacti of the genus Echinopsis. Our results suggest that moths might be important pollinators of columnar cactus species with nocturnal flowers in the extra-tropical deserts of South America.     

Positive effects of forest edges on plant reproduction: literature review and a case study of bee visitation to flowers of

Positive effects of fragmentation on plant reproduction are uncommon; in a literature review we found significant negative effects on fruit or seed set for 50 plant species, compared to 26 species showing no effect, and only nine affected positively. One of these is the declining New Zealand mistletoe Peraxilla tetrapetala (Loranthaceae), and here we investigate the mechanism of this positive effect. P. tetrapetala requires visits from native bird or bee pollinators to produce fruit. Fruit set was consistently pollen limited at several South Island sites because of a shortage of pollinators, but within a site at Lake Ohau, plants on forest edges had higher fruit set than those in the forest interior. Previous work showed that this difference was not caused by a shortage of resources in interior plants, but was associated with higher bird visitation rates to flowers on edges. In this study, we tested whether native bees also show a preference for edge flowers. At two sites (Ohau and Craigieburn) edge mistletoes had higher visitation by native bees (Hylaeus agilis and Leioproctus sp.) and higher fruit set. Some, but not all, of the higher visitation to edge flowers was explained by a preference amongst bees for flowers in direct sunshine. Therefore, P. tetrapetala experiences higher fruit set on edges because both of its main groups of pollinators (endemic birds and bees) visit edge flowers more often. The other eight published cases of positive effects of fragmentation on fruit set also all reported increased visitation rates by pollinators.     

In a world of white,flower colour matters: A white–purple transition signals lack of reward in an alpine Euphrasia

The New Zealand alpine flora displays a range of unusual characteristics compared with other alpine floras, in particular the high frequency of species with small white flowers. The presence of both white and bright purple flowers on the same plant in the New Zealand alpine annual creeping eyebright (Euphrasia dyeri Wettst.) provides an ideal opportunity to investigate the significance of flower colour in an environment where coloured flowers are rare. The relationships among flower age, gender phase, reward availability and petal colour were assessed in natural populations of E. dyeri. The effect of pollination on flower colour was tested using hand pollination of bagged flowers. Direct observations and videos of flowers were used to assess patterns of flower visitation by native and introduced pollinators. Unpollinated white E. dyeri flowers changed from white to purple within 6 days. However, pollination of white flowers triggered a significantly faster colour change, typically within 1–2 days. White flowers had receptive stigmas, large amounts of lipid‐rich pollen and small amounts of nectar, whereas stigmas of purple flowers are not receptive and flowers did not provide pollen or nectar rewards. Flowers were mainly visited by native syrphid flies. Both native syrphids and introduced Bombus bees showed a marked avoidance of purple flowers, tending to preferentially visit white flowers. Our study suggests that flower colour change from white to bright purple in E. dyeri functions to direct pollinators to rewarding, receptive flowers. As many Euphrasia L. species are described as having variably coloured flowers, this mechanism may be more widespread in the genus. Furthermore, our results add to the growing evidence that the dominance of white flowers in the New Zealand alpine is not simply due to a lack of colour discrimination among pollinators.     

Opportunistic nectar-feeding birds are effective pollinators of bird-flowers from Canary Islands: experimental evidence from Isoplexis canariensis (Scrophulariaceae)

Insular floras, characterized by simple pollination networks, sometimes include novel mutualistic agents such as nonspecialist nectarivores. In this study we confirmed the effective pollination of Isoplexis canariensis by opportunistic nectar-feeding birds in Tenerife, Canary Islands, Spain. This plant is among the ornithophilous species of the Canarian flora that lack past and present specialist nectarivorous birds. Experimental hand pollinations revealed self-compatibility, but cross-pollinated flowers produced a greater percentage of viable seeds than self-pollinated ones. Flowers were visited by five species of birds (Phylloscopus canariensis, Parus caeruleus, Sylvia melanocephala, Serinus canarius, and Fringilla coelebs) and by the endemic lizard (Gallotia galloti, Lacertidae). Insect pollination was absent, and the few insect visitors acted as nectar thieves or secondary nectar robbers. Birds represented 93.1% of total visits, with the Canarian Chiffchaff, Ph. canariensis, being the most frequent visitor. Flowers visited by birds set more, larger, and heavier fruit than flowers from which birds were excluded. Bird visitation also enhanced seed viability. These results demonstrate the active role of these opportunistic birds as effective pollinators of this Canarian bird-flower species. Further, the results reveal the need to consider the effect of these birds on the evolution of ornithophilous floral traits in absence of specialist nectarivores.