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Flowers exhibit great intra-specific variation in the rewards they offer. At any one time, a significant proportion of flowers often contain little or no reward. Hence, foraging profitably for floral rewards is problematic and any ability to discriminate between flowers and avoid those that are less rewarding will confer great advantages. In this study, we examine discrimination by foraging bees among flowers of nasturtium, Tropaeolum majus. Bee visitors included carpenter bees, Xylocopa violacea, which were primary nectar robbers; honeybees, Apis mellifera, which either acted as secondary nectar robbers or gathered pollen legitimately and bumblebees, Bombus hortorum, which were the only bees able to gather nectar legitimately. Many flowers were damaged by phytophagous insects. Nectar volume was markedly lower in flowers with damaged petals (which were also likely to be older) and in flowers that had nectar-robbing holes. We test whether bees exhibit selectivity with regards to the individual flowers, which they approach and enter, and whether this selectivity enhances foraging efficiency. The flowers approached (within 2 cm) by A. mellifera and B. hortorum were non-random when compared to the floral population; both species selectively approached un-blemished flowers. They both approached more yellow flowers than would be expected by chance, presumably a reflection of innate colour preferences, for nectar standing crop did not vary according to flower colour. Bees were also more likely to accept (land on) un-blemished flowers. A. mellifera gathering nectar exhibited selectivity with regards to the presence of robbing holes, being more likely to land on robbed flowers (they are not able to feed on un-robbed flowers). That they frequently approached un-robbed flowers suggests that they are not able to detect robbing holes at long-range, so that foraging efficiency may be limited by visual acuity. Nevertheless, by using a combination of long-range and short-range selectivity, nectar-gathering A. mellifera and B. hortorum greatly increased the average reward from the flowers on which they landed (by 68% and 48%, respectively) compared to the average standing crop in the flower population. Overall, our results demonstrate that bees use obvious floral cues (colour and petal blemishes) at long-range, but can switch to using more subtle cues (robbing holes) at close range. They also make many mistakes and some cues used do not correlate with floral rewards.

The global trade of species promotes diverse human activities but also facilitates the introduction of potentially invasive species into new environments. As species ignore national boundaries, unilateral national decisions concerning species trade set the stage for transnational species invasion with significant conservation, economic and political consequences. The need for a coordinated approach to species importation policies is demonstrated by the introduction of two bumblebee species into Chile for crop pollination, despite Argentina banning commercial importation of alien bumblebees based on expert opinion. The large garden bumblebee, Bombus ruderatus, was first introduced in 1982, and the buff‐tailed bumblebee, Bombus terrestris, has been continually introduced since 1997 as part of the burgeoning bumblebee trade. Both species have subsequently invaded southern South America. Today, the consequences of the growth of the bumblebee trade for agricultural pollination ranks among the top 15 emerging environmental issues likely to affect global diversity. Documented impacts of these invasions include the severe decline and local extinctions of the sole native Patagonian bumblebee, Bombus dahlbomii, pathogen transmission, flower damage and nectar robbing of native and cultivated plants. Policy implications. The South American bumblebee invasions portrayed here should alert governments to the unintended consequences of the booming international bee trade. More broadly, this case demonstrates that one country's importation decisions can have policy implications for its neighbours without consultation. Regrettably, coordinated international measures to prevent species invasions are seldom considered in South America or elsewhere, despite existing legal frameworks. The bumblebee case and others provide stark evidence of the pressing need for coordinated specific and general international policies concerning global species trade and their implementation.

Nectar robbers use a hole made in the perianth to extract nectar. Since robbers may modify plant fitness, they play an important role by driving evolution on floral traits, shaping population structure and influencing community dynamics. Although nectar robbing is widespread in angiosperms, the causes and ecological implications of this behaviour on large ecological scales are still unexplored. Our aim is to study the frequency of nectar robbing in plants of temperate and tropical regions and examine its association with plant traits. We characterised the levels of nectar robbing in 88 species of Mediterranean, Alpine, Antillean and Andean plant communities and identified the most important nectar robbers. We analysed associations between the levels of robbing and floral morphology, production and density of energy rewards, mechanisms of protection against nectar robbers, plant life form and geographic origin. Nectar robbing was present at all sampling sites. Within communities two patterns of robbing levels related to the diversity and specialization of robbers were detected. In most communities one plant species presented very high levels of robbing while other species had intermediate to low robbing levels. There, nectar robbers are opportunists, robbing highly rewarding plants. In the Andean community the high specialization of several co‐existing flowerpiercers produced an even pattern of robbing levels in the plant community. Plants with long flowers, abundant nectar and a high energy density are more likely to be robbed by both insects and birds. A high aggregation of the flowers within the plants and the presence of long calyxes and bracts are associated to low robbing rates by insects and to a lesser extent by birds. Besides the morphological constraints that operate on a single flower basis, nectar robbing is a phenomenon dependent upon the density of energy rewards reflecting the presence of mechanisms on higher ecological scales.

Florivory (flower consumption) occurs worldwide in modern angiosperms, associated with pollen and nectar consumption. However, florivory remains unrecorded from fossil flowers since their Early Cretaceous appearance. We test hypotheses that earliest angiosperms were pollinated by a diverse insect fauna by evaluating 7858 plants from eight localities of the latest Albian Dakota Formation from midcontinental North America, in which 645 specimens (8.2%) were flowers or inflorescences. Well-preserved specimens were categorized into 32 morphotypes, nine of which displayed 207 instances of damage from 11 insect damage types (DTs) by four functional-feeding groups of hole feeding, margin feeding, surface feeding and piercing-and-sucking. We assessed the same DTs inflicted by known florivores on modern flowers that also are their pollinators, and associated insect mouthpart types causing such damage. The diverse, Dakota florivore–pollinator community showed a local pattern at Braun’s Ranch of flower morphotypes 4 and 5 having piercing-and-sucking as dominant and margin feeding as minor interactions, whereas Dakotanthus cordiformis at Rose Creek I and II had an opposite pattern. We found no evidence for nectar robbing. These data support the rapid emergence of early angiosperms of florivore and associated pollinator guilds expressed at both the local and regional community levels.

Not all floral visitors attracted to flowers are pollinators. Instead, some visitors circumvent the floral opening, usually removing nectar without contacting the anthers and or stigma. Here we review the evolutionary ecology of nectar robbing from both the plant and animal perspective. Effects of robbing on female and male components of plant reproduction range from negative to positive. Their underlying mechanisms are diverse, including direct effects and indirect effects mediated through changes in pollination. We detail how plants may be able to deter robbers through morphological and chemical traits. For the evolutionary ecology of robbing to move beyond a phytocentric perspective, studies must also address the causes of robbing and the consequences for both robbers and pollinators. We use an energetics approach to evaluate these causes and consequences. Finally, we highlight unanswered questions in need of further research.

Invasive pollinators can disrupt native pollination mutualisms. We investigated the impact of the invasion of the European bumble bee Bombus terrestris in NW Patagonia, Argentina, on the pollination mutualism between the native legume Vicia nigricans and its main pollinator, the native bumble bee B. dahlbomii, and its consequences on plant reproduction. We assessed visitation frequency by both bumble bees and reproductive output of V. nigricans across space (in 12 sites) and time (over five seasons, from 1999 to 2012), before and after invasion in 2006. In 2012, we studied the behavior, visitation frequency, and nectar consumption by both bumble bees, the nectar consumed, the quantity and quality of pollen deposited and the reproductive output of V. nigricans in a subset of five sites across a gradient of B. terrestris invasion. Six years after invasion, B. terrestris became the most frequent visitor and nectar robber of V. nigricans flowers, while visits by B. dahlbomii dropped by 50%, fruit set by 43% and seeds per fruit by 32%. This detrimental effect on plant reproduction resulted from the high frequency of nectar robbing by B. terrestris, the nectar depletion, and the concomitant reduction of legitimate visits by the native bumble bee, which in turn lead to a decreased deposition of high quality pollen. Our study demonstrates that biological invasions can alter ecological interactions by replacing a plant-pollinator mutualism by a plant-nectar robber antagonism, hence disrupting plant reproduction and undermining long-term population viability. This conclusion raises the urgent need to regulate the international trade of non-native pollinators.

It has been suggested that the dynamics of nectar replenishment could differ for flowers after being nectar robbed or visited legitimately, but further experimental work is needed to investigate this hypothesis. This study aimed to assess the role of nectar replenishment in mediating the effects of nectar robbing on pollinator behaviour and plant reproduction. Plant-robber-pollinator interactions in an alpine plant, Salvia przewalskii , were studied. It is pollinated by long-tongued Bombus religiosus and short-tongued B. friseanus , but robbed by B. friseanus . Nectar production rates for flowers after they were either robbed or legitimately visited were compared, and three levels of nectar robbing were created to detect the effects of nectar robbing on pollinator behaviour and plant reproduction. Nectar replenishment did not differ between flowers that had been robbed or legitimately visited. Neither fruit set nor seed set was significantly affected by nectar robbing. In addition, nectar robbing did not significantly affect visitation rate, flowers visited within a plant per foraging bout, or flower handling time of the legitimate pollinators. However, a tendency for a decrease in relative abundance of the pollinator B. religiosus with an increase of nectar robbing was found. Nectar robbing did not affect female reproductive success because nectar replenishment ensures that pollinators maintain their visiting activity to nectar-robbed flowers. Nectar replenishment might be a defence mechanism against nectar robbing to enhance reproductive fitness by maintaining attractiveness to pollinators. Further studies are needed to reveal the potential for interference competition among bumble bees foraging as robbers and legitimate visitors, and to investigate variation of nectar robbing in communities with different bumble bee species composition.

We documented the diurnal pattern of nectar volumes in flowers of seven Neotropical hummingbird-pollinated plant species that were open to flower visitors and compared these standing crop data to nectar volumes in flowers protected from visitors. Standing crop of nectar bore little relationship to nectar in bagged flowers either in terms of volume or temporal pattern of availability. There was almost no nectar in open flowers except in those collected at dawn and those of Aphelandra sinclairiana; these were apparently too abundant to be depleted by visitors. Nectar volumes in open flowers were even more variable than in bagged flowers. We argue that understanding the evolution of plant-pollinator interactions requires understanding the relationship between nectar production and standing crop, as well as the impact of high variability on decisions by foraging animals. We conducted experiments to determine the effect of nectar removal on nectar production. Nectar removal via simulated legitimate visits had no impact on total production in flowers of Pavonia, Isertia, and Palicourea. For A. sinclairiana and Pentagonia, total nectar production in visited flowers was reduced compared to unvisited flowers. Data from individuals of these last two species indicated that the population-level pattern was assembled from individuals that responded differently to nectar removal; clearly, understanding the evolution of nectar traits demands data from individuals. We argue that detecting patterns of plant responses to nectar removal requires the context of floral characteristics (e.g., longevity, ovule number, or pollinators). Nectar removal via simulated nectar-robbing visits had no impact on total nectar production in A. sinclairiana but reduced total production in Isertia. Nectar robbing did not cause plants to invest more energy in nectar than they would have the absence of robbing. Finally, we found no difference in seed set by robbed and unrobbed flowers of A. sinclairiana. Our results add to a growing body of literature suggesting that nectar robbers are not always detrimental to plant fitness. /// Documentamos los patrones diurnos de volúmenes de néctar en flores que estaban disponibles para sus visitantes florales y los comparamos con los volúmenes de néctar de flores protegidas de visitantes, en siete especies de plantas neotropicales polinizadas por colibríes. Los volúmenes de néctar disponibles (standing crop) tuvieron poca relación con los volúmenes de néctar y sus patrones de disponibilidad en flores embolsadas. Las flores abiertas casi no presentaron nectar, con la excepción de las flores colectadas al amanecer y las flores de Aphekndra sinclariana; las cuales aparentemente eran demasiado abundantes para ser vaciadas por visitantes. Los volúmenes de nectar fueron aun más variables en las flores abiertas que en las flores embolsadas. Argumentamos que para entender la evolución de las interacciones planta-polinizador requiere tanto entender la relación entre producción de néctar y volúmenes de néctar disponibles, como el impacto que la alta variabilidad de producción de nectar tiene sobre las decisiones de forrajeo de los animales. Por lo tanto, llevamos a cabo experimentos para determinar el efecto que la remoción de néctar tiene sobre sus patrones de producción. La remoción de néctar, por medios que simulan las visitas legítimas, no tuvo impacto en la producción total de néctar de las flores de Pavonia, Isertia, y Palicourea. En A. sinclariana y Pentagonia, la producción total de néctar en flores visitadas fue menor que en las que no lo fueron. Datos de diferentes individuos de estas dos especies indican que el patrón a nivel poblacional esta formado por individuos que responden de manera diferente a la remoción de néctar; claramente, el entender la evolución de las características del néctar requiere datos a nivel de individuos. Argumentamos que detectar patrones de respuesta de las plantas a la remoción de néctar requiere conocer las características florales (e.g., longevidad, número de óvulos, polinizadores). La remoción de néctar, por medios que simular visitas de robadores de néctar, no afectó la producción de nectar de A. sinchiriana, pero redujo la producción total en Isertia. El robo de néctar no provocó que las plantas invirtieran más energía en nectar que la que hubieran utilizado en ausencia de robo. Finalmente, no encontramos diferencias en la producción de semillas de flores robadas o no robadas de A. sinclairiana. Nuestros resultados se suman a los de otros trabajos que sugieren que los robadores florales no siempre tienen efectos negativos sobre la adecuación de las plantas.

Fruit bats provide valuable pollination services to humans through a unique coevolutionary relationship with chiropterophilous plants. However, chiropterophily in the Old World and the pollination roles of large bats, such as flying foxes (Pteropus spp., Acerodon spp., Desmalopex spp.), are still poorly understood and require further elucidation. Efforts to protect these bats have been hampered by a lack of basic quantitative information on their role as ecosystem service providers. Here, we investigate the role of the locally endangered island flying fox Pteropus hypomelanus in the pollination ecology of durian (Durio zibethinus), an economically important crop in Southeast Asia. On Tioman Island, Peninsular Malaysia, we deployed 19 stations of paired infrared camera and video traps across varying heights at four individual flowering trees in a durian orchard. We detected at least nine species of animal visitors, but only bats had mutualistic interactions with durian flowers. There was a clear vertical stratification in the feeding niches of flying foxes and nectar bats, with flying foxes feeding at greater heights in the trees. Flying foxes had a positive effect on mature fruit set and therefore serve as important pollinators for durian trees. As such, semi‐wild durian trees—particularly tall ones—may be dependent on flying foxes for enhancing reproductive success. Our study is the first to quantify the role of flying foxes in durian pollination, demonstrating that these giant fruit bats may have far more important ecological, evolutionary, and economic roles than previously thought. This has important implications and can aid efforts to promote flying fox conservation, especially in Southeast Asian countries. Camera‐trapping shows that flying foxes (Pteropus hypomelanus) contribute to reproductive success of the durian (Durio zibethinus) tree. This new evidence of chiropterophily in the Palaeotropics shows how large fruit bats can also play a role in the production of economically important fruit.