Reproduction of <Emphasis Type="Italic">Amorpha canescens</Emphasis> (Fabaceae) and diversity of its bee community in a fragmented landscape

Loss of insect pollinators due to habitat fragmentation often results in negative effects on plant reproduction, but few studies have simultaneously examined variation in the bee community, site characteristics and plant community characteristics to evaluate their relative effects on plant reproduction in a fragmented habitat. We examined the reproduction of a common tallgrass prairie forb, Amorpha canescens (Fabaceae), in large (>40 ha) and small (<2 ha) prairie remnants in Iowa and Minnesota in relation to the diversity and abundance of its bee visitors, plant population size, and species density of the forb flowering community. We found significant positive effects of the diversity of bees visiting A. canescens on percent fruit set at a site in both years of the study and in 2002 an additional significant positive effect of plant species density. Abundance of bees visiting A. canescens had a significant positive effect on percent fruit set in 2002, but was only marginally significant in 2003. In 2003 but not 2002, the plant species density at the sites had a significant negative effect on the diversity and abundance of bees visiting A. canescens, indicating community-level characteristics can influence the bee community visiting any one species. Site size, a common predictor of plant reproduction in fragmented habitats did not contribute to any models of fruit set and was only marginally related to bee diversity one year. Andrena quintilis, one of the three oligolectic bee species associated with A. canescens, was abundant at all sites, suggesting it has not been significantly affected by fragmentation. Our results show that the diversity of bees visiting A. canescens is important for maintaining fruit set and that bee visitation is still sufficient for at least some fruit set in all populations, suggesting these small remnants act as floral resource oases for bees in landscapes often dominated by agriculture.     

Solitary and social bees as pollinators of Wahlenbergia (Campanulaceae): single-visit effectiveness, overnight sheltering and responses to flower colour

Solitary bees often form specialised mutualisms with particular plant species, while honeybees are considered to be relatively opportunistic foragers. Thus, it may be expected that solitary bees are more effective pollinators than honeybees when foraging on the same floral resource. To test this, we studied two Wahlenbergia species (Campanulaceae) in South Africa that are visited by both social honeybees and solitary bees, and which are shown here to be genetically self-incompatible and thus reliant on pollinator visits for seed production. Contrary to expectation, the solitary bee Lipotriches sp. (Halictidae) and social bee Apis mellifera (Apidae), which were the two most frequent visitors to flowers of the study species, were equally effective pollinators in terms of the consequences of single visits for fruit and seed set. Both bee species preferentially visited female phase flowers, which contain more nectar than male phase flowers. Male solitary bees of several genera frequently shelter overnight in flowers of both Wahlenbergia species, but temporal exclusion experiments showed that this behaviour makes little contribution to either seed production or pollen dispersal (estimated using a dye particle analogue). Manipulation of flower colour using a sunscreen that removed UV reflectance strongly reduced visits by both bee groups, while neither group responded to Wahlenbergia floral odour cues in choice tests. This study indicates that while flowers of Wahlenbergia cuspidata and W. krebsii are pollinated exclusively by bees, they are not under strong selection to specialise for pollination by any particular group of bees.     

Reproductive biology and pollinators of the invasive shrub Autumn olive (Elaeagnus umbellata Thunberg)

This study examined the reproductive biology of the invasive nitrogen-fixing shrub Elaeagnus umbellata. Hand-pollination experiments and pollinator-exclusion experiments were performed in four Illinois, U.S.A. populations to determine the breeding system of E. umbellata, and floral visitors were collected to determine pollinators in the invasive range. Although self-compatibility is a trait shown to confer invasiveness, our experiments revealed that E. umbellata is a mostly outcrossing species with a self-incompatible breeding system. Variation does exist in that a small percentage of individuals allow self-fertilization through autogamy. There is also variability among plants in the separation of male and female floral parts that may further affect selfing potential. The majority of floral visitors to E. umbellata were generalist pollinators, including bees, flies, and moths. Many of the larger insect visitors are pollinators of E. umbellata based on analysis of pollen on insect specimens, but smaller insects do not pollinate as frequently. Its ability to attract generalist pollinators means that E. umbellata will produce fruit wherever pollinators and mates occur; however, the low fruit set on open-pollinated branches contrasts with the idea of a prolifically fruiting plant. E. umbellata seems to serve as a reliable food source for many ecologically and economically significant insects, including native bumble bees (Bombus), the exotic honey bee (Apis mellifera), and armyworm (Mythimna unipuncta), a crop pest.     

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.     

Contribution of native bees and Africanized honey bees (Hymenoptera:Apoidea) to Solanaceae crop pollination in tropical México

In the tropics the contribution of bees as pollinators of important economic indigenous crops remains largely undocumented. We studied the diversity of bee species visiting indigenous tomato (Solanum lycopersicon) and habanero pepper (Capsicum chinense) in subtropical Yucatán, México. The contribution of two native bees, Exomalopsis (E) and Augochloropsis (AG) was compared with that of the introduced Africanized Apis mellífera (HB) for pollinating unvisited flowers in both crops. Apis mellífera and stingless bees were dominant in habanero pepper but solitary bee species were important visitors of tomato. In spite of both crops being autogamic, there was a significant contribution of native bees for pollination of both tomato and habanero pepper. The comparison of fruit weight, number of seeds, and a pollination index based on the latter showed that E and AG were more effective pollinators compared to HB in both crops (ca. Spear’s index of ca. 0.7 vs. 0.35 respectively). In tomato, a further evaluation of the contribution to pollination provided by the three bee species was made using the rate of visits to flowers. Although E and AG were the most efficient pollinators at single flower visits in tomato, none of the three species (including HB) were able to provide single visits to all flowers per unit time to the crop. Our results underline the importance of maintaining diverse assemblages and abundant populations of bee species that can synergically contribute to the productivity of tomato and hot pepper in the Neotropics.     

Pollination ecology of Yucca elata

The pollination biology of a population of 250 Yucca elata (Liliaceae) plants was studied in southern New Mexico. Yucca elata and the prodoxid yucca moth Tegeticula yuccasella have a mutualistic association that is essential for the successful sexual reproduction of both species. However, a wide range of other invertebrate species visit flowers during the day and at night. Our aim was to quantify the role of yucca moths and other invertebrate visitors in pollination and fruit set, using manipulative field experiments. Inflorescences were bagged during the day or night (N=12 inflorescences) to restrict flower visitors to either nocturnal or diurnal groups. Yucca moths were active exclusively nocturnally during the flowering period and thus did not visit inflorescences that were unbagged during the day. None of the 4022 flowers exposed only to diurnal visitors set fruit, whereas 4.6% of the 4974 flowers exposed only to nocturnal visitors (including yucca moths) produced mature fruit. The proportion of flowers producing fruit in the latter treatment was not significantly different from unbagged control inflorescences. In a series of experimental manipulations we also determined that: (1) flowers opened at dusk and were open for two days on average, but were only receptive to pollen on the first night of opening; (2) pollen must be pushed down the stigmatic tube to affect pollination; and (3) most plants require out-cross pollination to produce fruit. The combination of these results strongly suggests that yucca moths are the only species affecting pollination in Y. elata, and that if another species was to affect pollination, it would be a rare event.     

Reduced abundance and earlier collection of bumble bee workers under intensive cultivation of a mass‐flowering prairie crop

One of the most commonly seeded crops in Canada is canola, a cultivar of oilseed rape (Brassica napus). As a mass‐flowering crop grown intensively throughout the Canadian Prairies, canola has the potential to influence pollinator success across tens of thousands of square kilometers of cropland. Bumble bees (Bombus sp.) are efficient pollinators of many types of native and crop plants. We measured the influence of this mass‐flowering crop on the abundance and phenology of bumble bees, and on another species of social bee (a sweat bee; Halictus rubicundus), by continuously deploying traps at different levels of canola cultivation intensity, spanning the start and end of canola bloom. Queen bumble bees were more abundant in areas with more canola cover, indicating that this crop is attractive to queens. However, bumble bee workers were significantly fewer in these locations later in the season, suggesting reduced colony success. The median collection dates of workers of three bumble bee species were earlier near canola fields, suggesting a dynamic response of colonies to the increased floral resources. Different species experienced this shift to different extents. The sweat bee was not affected by canola cultivation intensity. Our findings suggest that mass‐flowering crops such as canola are attractive to bumble bee queens and therefore may lead to higher rates of colony establishment, but also that colonies established near this crop may be less successful. We propose that the effect on bumble bees can be mitigated by spacing the crop more evenly with respect to alternate floral resources.     

Pollination in Geonoma macrostachys and Three Congeners,G. acaulis,G. gracilis,and G. interrupta

A continuous 15 month study of the floral ecology of four syntopic understorey palm species of Genoma was conducted in Amazonian Peru lowland rainforest. The spicate inflorescences of G. macrostachys, G. acaulis and G. gracilis are strictly protandrous and the plants are functionally dioecious. Data suggest that in G. macrostachys and G. acaulis pollination is based on a mimicry system, the pistillate flowers mimicking the staminate ones in colour, shape and scent. Pollen-collecting meliponine bees (Hymenoptera, Apidae, Meliponinae) and pollen-feeding syrphid flies (Diptera, Syrphidae) which visit inflorescences during both sexual stages are the pollinators of G. macrostachys. Geonoma acaulis is pollinated by small pollen-feeding weevils (Coleoptera, Curculionidae, Derelomini) that visit male and female spikes. Additionally, in G. macrostachys another pollinator type, viz. euglossine bees (Hymenoptera, Apidae, Euglossinae), which are attracted and rewarded by both types of flowers may account for long-distance pollination. The palm G. gracilis shows a very distinct pollination system. Although opportunistic insect visitors are attracted to the inflorescences of this species it seems to be mainly anemophilous because pollen becomes powdery during an thesis. The branched inflorescences of G. interrupta are also protandrous, but unlike the other species of Geonoma observed, staminate and pistillate anthesis of individual flowers are, for the most, overlapping. A broad spectrum of visitors is attracted (bees, wasps, flies, and beetles), which all may act as pollinators. Outcrossing is especially encouraged during the purely female phase at the end of the flowering cycle when there are no more staminate flowers in the inflorescence. Effects on the reproductive biology and population structure of different pollination systems and breeding system are discussed.     

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.     

THRIPS-MEDIATED SELF-POLLINATION OF TWO FACULTATIVELY XENOGAMOUS WETLAND SPECIES

Thrips and/or aphids played an important role in the self-pollination of two facultatively xenogamous herbs that inhabit wetlands in northwestern Iowa. In both Ranunculus sceleratus and Potentilla rivalis the fruit set and/or successful pollination of plants that were sprayed with malathion to kill thrips and aphids and caged to exclude typical flower visitors was substantially and significantly lower than that of open-pollinated and caged plants. We observed pollenbearing thrips and aphids on the flowers. The high fruit sets of emasculated flowers of R. sceleratus showed that insects moved pollen between flowers, and our observations of bees collecting pollen and moving between plants suggest that cross-pollination can occur in both species.     

Pollination of Campomanesia phaea (Myrtaceae) by night‐active bees: a new nocturnal pollination system mediated by floral scent

• Bees are the most important diurnal pollinators of angiosperms. In several groups of bees a nocturnal/crepuscular habit developed, yet little is known about their role in pollination and whether some plants are adapted specifically to these bees. We used a multidisciplinary approach to investigate the reproductive biology and to understand the role of nocturnal/crepuscular bees in pollination of Campomanesia phaea (Myrtaceae), popularly named cambuci.
• We studied the floral biology and breeding system of C. phaea. We collected the floral visitors and tested the pollinators' effectiveness. We also determined the floral scents released at night and during daytime, and studied behavioural responses of crepuscular/nocturnal bees towards these scents.
• The flowers of cambuci were self‐incompatible and had pollen as the only resource for flower visitors. Anthesis lasted around 14 h, beginning at 04:30 h at night. The flowers released 14 volatile compounds, mainly aliphatic and aromatic compounds. We collected 52 species of floral visitors, mainly bees. Nocturnal and crepuscular bees (four species) were among the most frequent species and the only effective pollinators. In field bioassays performed at night, nocturnal/crepuscular bees were attracted by a synthetic scent blend consisting of the six most abundant compounds.
• This study describes the first scent‐mediated pollination system between a plant and its nocturnal bee pollinators. Further, C. phaea has several floral traits that do not allow classification into other nocturnal pollination syndromes (e.g. pollinator attraction already before sunrise, with pollen as the only reward), instead it is a plant specifically adapted to nocturnal bees.

     

Recognition of scent marks in solitary bees to avoid previously visited flowers

Knowing how floral visitors forage efficiently among flowers is important to understanding plant-pollinator interactions. When bees search for rewarding flowers, they use several visual cues to detect the available floral resources. In addition to these cues, bees can recognize scent marks, which are olfactory cues left on flowers foraged by previous visitors. This behavior is well known in social bees, such as honeybees and bumblebees. Although solitary bees do not need to give information about which flowers were foraged to conspecifics, several pieces of evidence have indicated the use of scent marks. However, it is unknown whether the behavior is widely used in many different bee species. We investigated whether four different solitary bees, Colletes patellatus (Colletidae), Andrena prostomias (Andrenidae), Osmia orientalis (Megachilidae), and Tetralonia mitsukurii (Apidae), can recognize flowers that have been foraged previously by visitors within 3 min. All four bees showed rejection responses to flowers foraged by conspecifics. However, our results showed that responses to foraged flowers varied among bee species. The tendency of A. prostomias and T. mitsukurii to reject the foraged flowers was pronounced, while in C. patellatus and O. orientalis it was weak. In both A. prostomias and T. mitsukurii, the rejection rate of flowers foraged by conspecifics decreased as the time lag after the last visit increased. Both bees visited the flowers from which pollen or nectar had been artificially removed. We suggest that A. prostomias and T. mitsukurii would recognize scent marks left by previous visitors, while the other two bees would not recognize them so strongly. It is likely that the decision to use scent marks is dependent either on the richness of resources or on the complexity of floral structure.     

Tailoring your bee sampling protocol: Comparing three methods reveals the best approaches to capturing bees

1. Bees are prolific, vital pollinators in agricultural and natural settings, but some taxa are declining. Surveying bees is crucial to understand the needs of these taxa; however, we lack a fine-grained understanding of assemblages associated with different sampling methods that would enable us to analyse data range-wide.
2. Here we examine the difference in abundance and richness of bees (bee bowls and vane traps only) and bumble bees (genus Bombus; bee bowls, blue vane traps and target netting) sampled with these methods from mixed-grass prairie to alpine habitats in Wyoming, USA.
3. We collected four times more bees and twice as many genera of bees in vane traps than bee bowls. Vane traps captured more individuals of abundant genera than bee bowls.
4. Bombus species abundance did not vary between vane traps and target netting; however, richness was higher in vane traps. Bee bowls captured few Bombus species.
5. Overall, we recommend using vane traps to sample most bees, and a combination of vane traps and target netting to collect bumble bees. We evaluated how three sampling techniques perform when surveying for wild bees, which will aid in identifying declining species as well as monitoring species of conservation concern.

     

Diversity of native bee visitors of cucurbit crops (Cucurbitaceae) in Yucatán, México

Native bees in Yucatán, México are treatened by agricultural land uses that limit their food resources, alter their reproductive habitats and increase their mortality. Various species may disappear before their importance for regional agricultural productivity and ecosystem maintenance is known. In order to assess their assemblage as visitors of cucurbit crops, we sampled more than 2000 bee specimens on fourteen fields of pumpkin, cucumber, melon and watermelon from five localities between 1995 and 1997; sample units consisted of all bees collected by net sweeping in a given field during 25–30 accumulated hours on separate days. The fourteen samples comprised bees of six families, 29 genera and 58 species. Composition per sample ranged between 10 and 27 species and abundance between 28 and 444 individuals. Seven species (six genera) of Apidae, Anthophoridae and Halictidae comprised around 80% of all the individuals collected. Yet, diversity measures indicated intermediate to high evenness in most sampled bee assemblages, i.e. despite the frequent abundance of some species of Augochlora, Partamona, Ceratina, Trigona or Peponapis, other bee visitors were also relatively important, particularly in small samples. Individual samples of pumpkin bee visitors had significantly different evenness among themselves and to other cucurbit crops. The percent similarity and number of shared species among the fourteen samples were both usually low; lumping data per crop and locality showed, however, higher evenness and more common species than individual samples. Results are discussed in terms of future research priorities: natural history of tropical native bees and strategies to monitor bee community changes for conservation purposes.     

Reproductive biology of Ferocactus recurvus (Mill.) Borg subsp. recurvus (Cactaceae) in the Tehuacán‐Cuicatlán Valley,Mexico

• Mexico has one of the highest diversities of barrel cacti species worldwide; however, all are threatened and require conservation policies. Information on their reproductive biology is crucial, but few studies are available. Ferocactus recurvus subsp. recurvus is a barrel cactus endemic to the Tehuacán‐Cuicatlán Valley. Our research aimed to characterise its floral and pollination biology. We hypothesised bee pollination, as suggested by its floral morphology and behaviour, and self‐incompatibility, like most barrel cacti studied.
• Three study sites were selected in the semiarid Zapotitlán Valley, Mexico. We examined 190 flowers from 180 plants to determine: morphometry and behaviour of flowers, flower visitors and probable pollinators, and breeding system.
• Flowers showed diurnal anthesis, lasting 2–5 days, the stigma being receptive on day 2 or 3 after the start of anthesis. Flowers produced scarce/no nectar and main visitors were bees (Apidae), followed by flies (Muscidae), ants (Formicidae), thrips (Thripidae) and hummingbirds (Throchilidae); however, only native bees and occasionally wasps contacted the stigma and anthers. Pollination experiments revealed that this species is self‐incompatible and xenogamous. In natural conditions, fruit set was 60% and cross‐pollination fruit set was 100%. Percentage seed germination resulting from cross‐pollination was higher than in the control treatment.
• Our results provide ecological information for conservation programmes to ensure a high probability of breeding and seed production in natural populations of F. recurvus.

     

Long Tongues and Loose Niches: Evolution of Euglossine Bees and Their Nectar Flowers1

I examined relationships between tongue length of orchid bees (Apidae: Euglossini) and nectar spur length of their flowers in the genera Calathea, Costus, and Dimerocostus using phylogenetically independent contrasts. Long‐tubed flowers have specialized on one or several species of long‐tongued euglossine bees, but long‐tongued bees have not specialized on long‐tubed flowers. Whereas long tongues may have evolved to provide access to a wider variety of nectar resources, long nectar spurs may be a mechanism for flowers to conserve nectar resources while remaining attractive to traplining bee visitors.     

Bee visitors of <Emphasis Type="Italic">Centaurea solstitialis</Emphasis> L. (Asteraceae) in an urban environment in northwestern Turkey

Information on the pollination ecology and floral visitors of the noxious weed Centaurea solstitialis is available for several populations in its invasive range, but limited information is available in its native range, with most studies conducted on the Greek island of Lesvos. Herein, we document the visitation pattern of bees and explore the relationship of bee body size and nectar availability in weedy populations of C. solstitialis from an urban environment within its native range in northwestern Turkey. Studies were conducted at patches of C. solstitialis in abandoned lots at the Uluda? University near the city of Bursa. A total of 41 species, including honey bees, belonging to five families and 19 genera were recorded. Small megachilid and halictid bee species were the most common visitors. Average nectar standing crop volume per floret was low (0.003–0.117 μL) and did not significantly vary throughout the day. Average bee head width significantly correlated with average nectar standing crop volume but did not significantly change throughout the day. Analyses of pollen loads as well as direct observations of bee foraging behavior indicate that a large number of bees visit C. solstitialis, primarily in search of nectar while carrying a large percentage of pollen grains of this plant species on their bodies. These results are similar to previous observations on a non-weedy population of C. solstitialis from the island of Lesvos.     

Wild bee diversity is enhanced by experimental removal of timber harvest residue within intensively managed conifer forest

The use of timber harvest residue as an energy source is thought to have environmental benefits relative to food‐based crops, yet the ecological impact of this practice remains largely unknown. We assessed whether the abundance and diversity of wild bees (Apoidea) were influenced by the removal of harvest residue and associated soil compaction within managed conifer forest in western Oregon, USA. We sampled bees over two years (2014–2015) on study plots that were subjected to five treatments representing gradients in removal of harvest residue and soil compaction. We collected >7,500 bee specimens from 92 distinct species/morphospecies that represented five of the seven bee families. We trapped 3x more individuals in the second year of the study despite identical sampling effort in both years, with most trapped bees classified as ground‐nesting species. Members of the sweat bee family (Halictidae) comprised more than half of all specimens, and the most abundant genus was composed of metallic green bees (Agapostemon, 33.6%), followed by long‐horned bees (Melissodes, 16.5%), sweat bees (Halictus, 15.9%), and bumble bees (Bombus, 13.6%). In both years, abundance and observed species richness were greatest in the most intensive harvest residue treatment, with other treatments having similar values for both measures. Our study indicates that early successional managed conifer forest that has experienced removal of harvest residue can harbor a surprising diversity of wild bees, which are likely to have important contributions to the broader ecological community through the pollination services they provide.     

Inflorescence Height Affects Visitation Behavior of Bees–A Case Study of an Aquatic Plant Community in Bolivia1

We studied the bee fauna visiting a plant community of 10 species of flowering aquatic plants in an inundated savanna region in Bolivia. In total we observed 36 bee species in 17 genera at the flowers. Cluster analysis of the similarities among the plant species in terms of their visitor spectra showed a division into two groups: plants with inflorescence heights shorter than the grass height and plants with inflorescences projecting out of the surrounding vegetation. Larger bees of the genera Apis, Melipona, Bombus, and Xylocopa were observed only at flowers above the surrounding vegetation. Smaller, mainly solitary bees (e.g., Augochlorella, Ancyloscelis) visited flowers in the dense vegetation near the water surface. Analyses of the pollen loads revealed that most individuals were highly flower constant. When bees carried different pollen types, it was generally pollen from flowers within a single stratum. We discuss specialization, flower constancy, competition, and different foraging strategies as possible reasons for stratum fidelity.     

Pollinator effectiveness of native and non‐native flower visitors to an apparently generalist Andean shrub,Duranta mandonii (Verbenaceae)

Not all visitors to flowers are pollinators and pollinating taxa can vary greatly in their effectiveness. Using a combination of observations and experiments we compared the effectiveness of introduced honeybees with that of hummingbirds, native bees and moths on both the male and female components of fitness of the Andean shrub Duranta mandonii (Verbenaceae). Our results demonstrated significant variation among flower visitors in rates of visitation, pollen removal ability and contribution to fruit set. This variation was not always correlated; that is, taxa that regularly visited flowers did not remove the most pollen or contribute to fruit set. Despite the taxonomic diversity of visitors, the main natural pollinators of this shrub are large native bees, such as Bombus spp. Introduced honeybees were found to be as effective as native bees at pollinating this species. Duranta mandonii has high apparent generalization, but low realized generalization and can be considered to be a moderate ecological generalist (a number of species of large bees provide pollination services), but a functional specialist (most pollinators belong to a single functional group). The present study has highlighted the importance of measuring efficiency components when documenting plant–pollinator interactions, and has also demonstrated that visitation rates may give little insight into the relative importance of flower visitors.