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Simple Summary: Pollinators play a crucial role in the survival and reproduction of flowering plants, and different flowering plants rely on specific types of pollinators. This study focuses on Hibiscus syringae and explores the effect of pollinator size on pollination efficiency. The research results indicate that although the size of pollinators is an important factor, it is not the only variable that determines pollination efficiency. In fact, the behavior patterns of pollinators and the characteristics of plant flowers themselves also have a significant impact on the reproductive process of plants. These findings provide valuable scientific reference for understanding the reproductive mechanism of hibiscus. To understand the reproductive strategies of the typically introduced plant Hibiscus mutabilis and to compare the pollination efficiency of its different pollinators, we observed, measured, and recorded the flowering dynamics, floral traits, and visiting insects of H. mutabilis. Furthermore, we compared the body size, visitation rate, and pollination efficiency of the pollination insects of H. mutabilis. The results indicated that, despite exhibiting specialized moth pollination characteristics based on similarities in flower features to other moth-pollinated species, H. mutabilis actually presented a generalized pollination system. The nectar of H. mutabilis attracted a variety of insects to provide pollination services, a total of five flower visitors, one moth species (Macroglossum pyrrhosticta), and four bee species (Xylocopa appendiculata, Xylocopa dissimilis, Bombus breviceps, and Apis mellifera), were found to provide pollination services for H. mutabilis. The pollination efficiency of these pollinators was related to the parts of their body in contact with the stamens and stigmas of flowers. Although M. pyrrhosticta was larger in size and its visitation frequency in our field observations was higher, its pollination efficiency was lower. This was due to the small part of its body (proboscis) contacting the two sexual organs of H. mutabilis while visiting flowers, resulting in a low amount of pollen being transferred and deposited. In contrast, the bee pollinators' proboscis was significantly shorter than that of M. pyrrhosticta, and it must enter the flower to suck the nectar that is hidden deeply inside the base of the flower. Therefore, the body parts of bee pollinators in contact with the two sexual organs of H. mutabilis were larger than M. pyrrhosticta in the process of visiting flowers, and the pollination efficiencies were significantly higher than those of M. pyrrhosticta. In addition, larger bee pollinators have higher pollination efficiency. As a result, H. mutabilis suffered from pollen limitation due to the pollination efficiencies of the moth pollinators in the introduced habitats, but it compensated by attracting more species of bee pollinators. [ABSTRACT FROM AUTHOR]

Pesticides and the lack of floral resources are key drivers of insect decline in agricultural areas. Both land‐use stressors can have a variety of synergistic and sublethal effects on pollinators, affecting their health and foraging behaviour. Pollinating insects include species with vastly different life histories, giving them potentially different vulnerability and resilience to stressors. However, most research has generally focused on bees. Here, we contrast synergistic effects of nutritional stress and pesticide use on social bumblebees and solitary hoverflies.We experimentally tested the effects of the neonicotinoid acetamiprid and low‐quality food on health traits of Bombus terrestris workers and Episyrphus balteatus adults (ovarian development, body size and colony development or survival). The foraging behaviour of treated pollinators was recorded in a semi‐field setup and, for B. terrestris, we measured the pollen amount on the body surface and the pollen deposited on stigmata after a single floral visit.Both stressors affected bumblebee health. Additionally, insecticide‐treated workers showed increased flower handling times and flight durations, while low‐quality food reduced the amount of pollen on the surface of bumblebees and the pollen deposited on stigmata. Syrphids were mostly affected by low‐quality food, which decreased their survival probability and changed their foraging behaviour. Furthermore, we found an interactive effect between the two stressors, reducing E. balteatus ovary development.Synthesis and applications. Insecticide and food stress affected fitness traits of both bumblebees and syrphid flies, possibly reducing pollinator populations under natural conditions. Especially for bumblebees, long‐term exposure led to a reduction in the provision of pollination services, both by changing their behaviour and reducing pollen transfer. We found differences between the two pollinator groups, showing that results gained from single groups like bees should not be extrapolated to all pollinators. Interactive effects indicate potential buffering effects of high‐quality food against other stressors and highlight the importance of considering synergies between multiple stressors in risk assessments. This further emphasizes the relevance of floral resources such as wild flower strips in agricultural areas to conserve pollinators and pollination services. [ABSTRACT FROM AUTHOR]

Background and Aims Pollination failure occurs from insufficient pollen quantity or quality. However, the relative contributions of pollen quantity vs. quality to overall pollen limitation, and how this is affected by the co-flowering context, remain unknown for most plant populations. Here, we studied patterns of pollen deposition and pollen tube formation across populations of four predominately outcrossing species in the genus Clarkia to evaluate how the richness of co-flowering congeners affects the contribution of pollen quantity and quality to pollen limitation. Methods We partition variation in pollen deposition and pollen tube production across individuals, populations and species to identify the main sources of variation in components of reproductive success. We further quantify the relative contribution of pollen quantity and quality limitation to the reproductive success of the four Clarkia species using piecewise regression analyses. Finally, we evaluate how variation in the number of co-flowering Clarkia species in the community affects the strength of pollen quality and quality limitation. Results Across all contexts, pollen deposition and the proportion of pollen tubes produced varied greatly among individuals, populations and species, and these were not always correlated. For instance, C. xantiana received the smallest pollen loads yet produced the highest proportion of pollen tubes, while C. speciosa exhibited the opposite pattern. Yet, co-flowering richness had variable effects on the strength of pollen quantity and quality limitation among populations. Specifically, breakpoint values, which are an indicator of overall pollen limitation, were two-fold higher in the four-species community compared with one- and two-species communities for two Clarkia species, suggesting that pollen limitation can increase with increasing richness of co-flowering congeners. Conclusions Our results reveal a complex interplay between the quantity and quality of pollen limitation and co-flowering context that may have different evolutionary outcomes across species and populations. [ABSTRACT FROM AUTHOR]

Longer stigmas in short‐styled morphs of distylous plants have been considered an adaptive characteristic that increases intermorph pollen deposition. The greater pollen deposition in short‐styled stigmas may be a by‐product of their longer length, making deposition effectiveness comparison between morphs unfeasible. Thus, investigating which morph has the relatively most efficient stigma (i.e., pollen deposition per unit length) can boost our understanding of the adaptive significance of longer stigmas.Here, we compared pollen deposition between morphs relative to stigma length and assessed whether short‐styled stigmas are more, less, or equally effective in receiving pollen grains per unit length. We reviewed the literature to characterize the extent of sigma length differences between morphs using the two most speciose distylous genera as model systems: Palicourea and Psychotria (Rubiaceae). Then, we conducted a between‐morph comparison of raw and relative pollen depositions in a Palicourea rigida population.We confirmed that short‐styled stigmas were longer than long‐styled stigmas in both Palicourea (194.31% longer) and Psychotria (52.59% longer) flowers. Furthermore, in the focal Pal. rigida, although short‐styled stigmas were 268.04% longer and received 97.04% more pollen grains than long‐styled stigmas, the relative pollen deposition had a reverse pattern, with short‐styled stigmas being two‐times less efficient in receiving pollen.Our results indicate that the longer length of the short‐styled stigmas may have a compensatory effect, increasing the chances of pollen grains reaching the stigma and probably maintaining disassortative intermorph pollination in distylous plants. [ABSTRACT FROM AUTHOR]

Heterospecific pollen (HP) deposition varies widely among species in communities, which has been explicated by two adaptation strategies: HP avoidance and HP tolerance. Studies of the plant–pollinator network have uncovered that oceanic island communities are highly generalized and strongly connected. It remains unclear, however, which strategy prevails in such communities. We examined stigma pollen deposition on 29 plant species, and assessed patterns of HP load size and diversity in the Yongxing Island community. We assessed the effects of phenotypic specialization and species‐level network structural properties of plant species on pollen deposition among species. The hypothesis of three accrual patterns of HP within species was tested by illustrating the relationship between conspecific pollen (CP) and HP receipt. Extensive variation occurred among species in HP receipt, while 75.9% of species received less than 10% HP and one species received more than 40% HP throughout the community. Flower size strongly drives the variation of HP receipt, while network structural properties had no effect on the pollen receipt. Nineteen species showed no relationship between the number of HP and CP loads, and they received smaller HP load sizes and lower HP proportions. Most plant species evolved HP avoidance strategy, and HP receipt was an occasional event for most plant species in the generalized community. HP and CP receipts are independent of each other in plant species with the HP avoidance mechanism. Our results highlight that plants in the generalized pollination system may preferentially select to minimize the HP load on stigmas. [ABSTRACT FROM AUTHOR]

Pollination services are affected by landscape context, farming management and pollinator community structure, all of which impact flower visitation rates, pollen deposition and final production. We studied these processes in Argentina for highbush blueberry crops, which depend on pollinators to produce marketable yields.We studied how land cover and honeybee stocking influence the abundance of wild and managed pollinators in blueberry crops, using structural equation modelling to disentangle the cascading effects through which pollinators contribute to blueberry fruit number, size, nutritional content and overall yield.All pollinator functional groups responded to landscape changes at a spatial scale under 1000 m, and the significance or direction of the effects were modulated by the field‐level deployment of honeybee hives.Fruit diameter increased with pollen deposited, but decreased with honeybee abundance, which, had indirect effects on fruit acidity. Honeybees had a positive effect on the number of fruit produced by the plants and also benefited the overall yield (kg plant−1) through independent effects on both the quality and quantity components of fruit production.Synthesis and applications. Deployment of beehives in blueberry fields can buffer, but not compensate for the negative effects on honeybee abundance produced by surrounding large scale none‐flowering crops. Such compensation would require high‐quality beehives by monitoring their health and strength. The contribution of honeybees to crop production is not equal across production metrics. That is, higher abundance of honeybees increases the number of berries produced but at the cost of smaller and more acidic fruits, potentially reducing their market value. Growers must consider this trade‐off between fruit quantity and quality when actively managing honeybee abundance. [ABSTRACT FROM AUTHOR]

Insect pollinators affect pollen transfer dynamics, with consequences for pollen movement and the genetic structure of plant populations. Pollen transfer dynamics has not been previously examined in flowers with a tripping mechanism. Here we examine whether pollen accumulated on a bee’s body increases with the number of Medicago sativa L. flowers tripped by Bombus impatiens Cresson during a foraging bout, while controlling for bee body size and number of visited flowers. In a second experiment, we determine whether the number of revisits to a tripped flower increases pollen deposition onto the stigmas. We set up three M. sativa plants with a controlled number of racemes in a greenhouse room, and followed individual bees as they foraged, recording each plant, raceme, and flower visited. For pollen accumulated, we collected bees at the end of their foraging bout and counted pollen grains on their body. For pollen deposition, we collected flowers with between 0 and 6 revisits and counted the pollen grains on the stigmas. The number of pollen grains on a bee’s body increased with the number of flowers tripped in a foraging bout, but was not affected by the number of flowers visited or the size of individual bees. The number of pollen grains deposited on a stigma did not increase with the number of revisits to a tripped flower. This latter result contrasts with plants without a tripping mechanism where the number of visits increases pollen deposition and seed set. Tripping affects pollen transfer dynamics and we discuss how its effect may vary with the mode of tripping.

Pollen contains vegetative and generative cells that influence the seed set. Accurate pollen assessments help understand the breeding biology of oilseed rape. In order to evaluate the number of pollen grains in a large number of samples, an effective method should be designed. A new method was established to evaluate the pollen counts of five oilseed rape cultivars. This method mainly relies on 5% sucrose + 0.1% agar solution to suspend the pollen and uses a standard curve corresponding to the absorbance and the number of pollen grains to estimate the number of pollen grains. The linear fit formula of this standard curve was precision, and the R2 value between the pollen count and absorbance reached 0.998. Furthermore, the variation in the pollen counts at three flowering stages and on two kinds of stamens was assessed. The pollen count per flower varied significantly among oilseed rape cultivars and flowering stages (GLM: p

Seed production can be affected by water availability and also depend on the amount (pollen intensity) and quality of pollen deposited. The way pollen receipt on the stigma translates into seeds produced follows that of a saturating dose-response. Not only can water availability and pollen intensity each influence seed production, these factors could interact in their effects on seed production. Changes to the relationship between seed production and pollen intensity can in turn influence pollinator effectiveness and pollinator-mediated selection. We asked how water availability affected indices of plant fitness (seed set, fruit set and seed mass) and the relationship between pollen intensity and seed production in Phacelia parryi. We conducted a greenhouse experiment where we manipulated water availability (either high- or low-water) to pollen recipient plants and hand-pollinated each plant with a range of pollen intensities. We conducted 703 hand-pollinations on 30 plants. For each hand-pollinated flower we measured pollen deposited, seed production and seed mass. We then generated a piecewise regression of the relationship between pollen intensity and seed production, and determined average effects of water on plant fitness measures. This experiment was paired with a field observational study aimed to document natural variation in pollen deposition. Average seed production per fruit was 21 % higher in the high-watered plants. The relationship between pollen intensity and seed production differed between the two water treatments. Plants under high-water exhibited a wider range in which pollen deposition increased seed production. Average natural pollen intensities fell within different regions of the piecewise regression for low- and high-water plants. Water availability can alter the efficiency by which pollen received is translated into seeds produced. Our greenhouse data suggest that only under certain pollen intensity environments will water availability affect how pollen received is translated into seeds produced.

Several barriers contribute to reproductive isolation between plant species, which can be classified as pre- or post-pollination. Understanding the strength of these barriers could clarify the factors that maintain reproductive isolation and thus species integrity. In this study, we quantified reproductive isolation between two bat-pollinated co-occurring Bauhinia species (B. acuruana and B. pentandra) with similar flower morphology. Over the course of 18 months, we assessed reproductive isolation between these two Bauhinia species by quantifying the individual strengths and absolute contributions of five pre- and post- pollination barriers. Our data showed that both species are completely isolated in their reproduction by a combination of several barriers. Although they co-occur in a few populations, we found a high degree of geographic isolation between them. And although their flowering periods overlap, there is a significant difference in flowering peaks. Both species have the same pollinating bats, but the interspecific transfer of pollen between the plant species may be reduced due to the different length of the flower stamens, resulting in different pollen deposition on the bats' bodies. We have documented complete incompatibility between taxa and conclude that pre- and post-pollination barriers are important factors in preventing gene flow, even in contact zones between these two species of Bauhinia. We highlight that our work is the first study to use methods to estimate the strength of reproductive isolation barriers between bat-pollinated species. [ABSTRACT FROM AUTHOR]

Invasive plant species severely threaten natural plant communities around the world, especially for islands. As introduction rates rise, novel species interactions appear within ecosystems. Studies that focus on invasive plant impacts on native plants, especially on native communities, remain rare and their conclusions are mixed. We constructed ten quantitative plant-pollinator interaction networks and calculated five network-level structure metrics (interaction evenness, linkage density, specialization, weighted connectance, and weighted nestedness) along an Asteraceae invasion gradient in the Yongxing Island community. We calculated the species-level nestedness contribution of each plant species in each network, and compared the nestedness contribution differences between invasive Asteraceae and non-Asteraceae species. Stigmas of three native and four invasive Asteraceae species were collected, and their pollen grains were identified. We analyzed invasive Asteraceae species impacts on native pollination network structure and the pollen deposition of native plants. Both weighted nestedness and weighted connectance increased significantly as invasive Asteraceae became increasingly dominant. Invasive Asteraceae plants had higher nestedness contribution compared to native plants in most sites, and this difference increased as the Asteraceae proportion increased. Furthermore, in native plant species, the proportion of conspecific pollen grains on stigmas decreased significantly, while the proportion of Asteraceae pollen grains on stigmas increased significantly as Asteraceae invasion level increased. For the four Asteraceae species, the proportion of conspecific pollen grains was significantly higher than heterospecific and other Asteraceae pollen grains on the stigmas. These results significantly add to our understanding of how the structure of plant-pollinator interaction networks changes concomitantly with plant invasion intensity. Invasive Asteraceae increase community stability and persistence, and increase the heterospecific pollen deposition on stigmas of native plants as invasion level increases. Invasive plants may greatly shape network structure and maintain community stability in oceanic island systems. Heterospecific pollen avoidance may be crucial mechanism facilitating Asteraceae invasion success within native communities, together with their 'integration', into plant-pollinator interactions on the Yongxing Island. [ABSTRACT FROM AUTHOR]

AbstractTeak is an insect-pollinated species, and seed production depends on pollinators. The objectives of this study were to determine potential pollinators of teak and their foraging behavior in obtaining alternate food sources as the basis for management recommendations. Four traps, i.e. Moczarsky-Winkler selector traps, sticky traps, yellow-pan traps, and manual traps (insect net), were put up among blooming inflorescences during the flowering period of March to May. Insects were collected and counted weekly and identified. The presence and location of the pollen on their bodies were observed. The time and duration of foraging behavior, the duration of a single visit, the number of visits in an hour, and the landing position when approaching the teak flower as well as the understory were also observed. The result showed Ceratina sp., and Braunsapis sp. (Apidae), Nomia sp. (Halictidae) were potential teak pollinators in the CSO in East Java. The insect foraging behavior supports the ability to deposit pollen onto the stigma. The presence of Mimosa pudica in the understory plays as an alternate food source for pollinators. Intensive weeding and trimming of old or dead branches should be less practiced to enhance pollinators’ populations and nesting sites.

Staminal hairs are the particular appendages of stamens, which may affect pollinator foraging behaviour and pollen transfer. However, experimental evidence of the functions of staminal hairs in pollination remains scarce. Here, we conducted staminal hair manipulation experiments in Tradescantia fluminensis (Commelinaceae) to investigate their effects on visitation and pollen transfer by bees. Our observations revealed that both visitation rates and visit duration of honeybees (Apis cerana) to control flowers were significantly higher than that of hairless flowers. Moreover, removing the staminal hairs significantly decreased pollen deposition by honeybees (A. cerana), but did not affect pollen removal. The staminal hair was similar in length to the stamen and the pistil of T. fluminensis. The staminal hairs provide more footholds for honeybees, and they lay prone on the staminal hairs to collect pollen, which increased the accuracy of pollination through the consistent pollen placement and pick-up on the ventral surface of honeybees. These results showed that the staminal hairs in T. fluminensis may represent an adaptation to attract pollinators and enhance pollination accuracy. [ABSTRACT FROM AUTHOR]

Body size is a trait that can affect plant–pollinator interaction efficiency and plant reproductive success. We explored the impact of intraspecific size shifts on the interactions between pollinators and flowering plants under controlled conditions. We considered two development conditions leading to the production of large and small individual flowers of Borago officinalis and Echium plantagineum. We also used the natural variability of worker size within bumblebee colonies to isolate small and large workers. We performed a fully crossed experiment with the two flower sizes of each plant species and the two sizes of bumblebee workers. Our results show that the size of both partners did not affect bee foraging behavior in most of the evaluated parameters and both bee sizes were equally efficient in depositing pollen. Significant differences were found only in pollen deposition across the life of a flower in small flowers of B. officinalis, with the greatest quantity of pollen deposited by small bees. We did not find a relationship between pollinator size and plant fitness. Our results suggest that generalist plant–pollinator interactions may be resilient to future potential mismatches in the size of the partners but remain to be tested if they are still resilient under the new environmental conditions resulting from global changes. [ABSTRACT FROM AUTHOR]

The lack of pollinators in the oil tree peony field was a serious problem for the seed yield. In the preliminary studies, we found that the seed rate of oil tree peonies was significantly improved by supplementing bees during the flowering stages in the pollination net room. In addition, the performance of Apis mellifera L. was better than Bombus terrestris L. To understand the interaction relationship between flowering characteristics and the managed bees, and the pollen-collecting ability of different species of bees, the flowering traits and the pollen loaded on bees were measured in this study. We found that the bees visited flowers with preference and they prefer to forage the flowers having pollen with higher viability. The B. terrestris carried more pollen (27,000.00 ± 5613.70 grains) on the body surface than that of the A. mellifera (7690.00 ± 2873.26 grains). The A. mellifera outperformed B. terrestris both in pollen deposition per visit on the stigma and on the pollen transfer efficiency. The viability of pollen on the body surface (67.77% ± 19.06%) and hind legs (92.02% ± 10.74%) of A. mellifera were both significantly higher than that of B. terrestris (31.84% ± 4.84% and 83.77% ± 6.40%). Our study indicated that the quantity and quality of pollen loaded on stigma by A. mellifera were both better than B. terrestris, which provided evidence that the A. mellifera was the effective pollinator pollinating for the oil tree peony in the pollination net room. [ABSTRACT FROM AUTHOR]

Pollinator availability and effectiveness are important considerations in plant systems that depend on insect transfer of pollen. In mixed-flower systems (such as dioecious or gynodioecious systems), pollinators may distinguish between morphs, a behaviour which could have negative implications if it leads to reduced cross-pollination. We examined pollinator visitation, response, and effectiveness in hybrid canola seed production, a gynodioecious crop, to understand how pollinator behaviour contributes to cross-pollination between ‘male’ (hermaphroditic) and ‘female’ (male-sterile) morphs. The pollinator types found in these fields differ in visitation rate, size, and pollen load, factors that may affect pollen transfer between plants. The willingness of pollinators to move between male and female flowers can also affect pollen deposition. We used an interview bouquet to present unvisited female inflorescences to different pollinator types visiting male and female flowers to understand behavioural responses to floral morphs and the factors that contribute to better pollination effectiveness. Managed pollinators (honey and leafcutter bees) were far more abundant than wild pollinators in this system. Bees foraging on male flowers were less likely to accept a proffered female flower than those foraging on female flowers. Pollen deposition on stigmas was influenced by pollinator type (female leafcutter bees were the most effective) and increased with time spent on a flower. Pollinators transferring from a male flower to a female flower deposited more pollen than those that originated on female flowers, emphasizing the importance of transfer between male and female morphs. Surprisingly, pollinators carrying more pollen transferred less pollen to recipient stigmas.

Abstract The brown honeyeater (Lichmera indistincta) is a common bird species in Australia and is a pollinator of many native plant species but there are no records demonstrating evidence of effective pollination by honeyeaters in commercial cropping systems. We observed L. indistincta visiting rabbiteye blueberry flowers at a commercial berry orchard on the Mid North Coast of New South Wales and evaluated their capacity to transfer pollen. We did this by bagging flowers to prevent visitation prior to anthesis; after anthesis, we unbagged the flowers and waited for L. indistincta visits. After a single visit, we collected the stigma and mounted it on a slide to evaluate stigmatic pollen load. We observed the birds visiting blueberry flowers and foraging on nectar. We also found that L. indistincta deposited similar amounts of pollen to other common insect pollinator species, such as honeybees and stingless bees. As the commercial berry orchard blocks are surrounded by diverse remnant vegetation, we hypothesize that the vegetation is likely providing habitat for these birds. Our results indicate that berry growers with management practices that protect and support remnant vegetation surrounding blueberry orchard blocks may benefit from higher blueberry pollination services by supporting diverse pollinators within fields.

Introduced species can have cascading effects on ecological communities, but indirect effects of species introductions are rarely the focus of ecological studies. For example, managed honey bees (Apis mellifera) have been widely introduced outside their native range and are increasingly dominant floral visitors. Multiple studies have documented how honey bees impact native bee communities through floral resource competition, but few have quantified how these competitive interactions indirectly affect pollination and plant reproduction. Such indirect effects are hard to detect because honey bees are themselves pollinators and may directly impact pollination through their own floral visits. The potentially huge but poorly understood impacts that non‐native honey bees have on native plant populations combined with increased pressure from beekeepers to place hives in U.S. National Parks and Forests makes exploring impacts of honey bee introductions on native plant pollination of pressing concern. In this study, we used experimental hive additions, field observations, as well as single‐visit and multiple‐visit pollination effectiveness trials across multiple years to untangle the direct and indirect impacts of increasing honey bee abundance on the pollination of an ecologically important wildflower, Camassia quamash. We found compelling evidence that honey bee introductions indirectly decrease pollination by reducing nectar and pollen availability and competitively excluding visits from more effective native bees. In contrast, the direct impact of honey bee visits on pollination was negligible, and, if anything, negative. Honey bees were ineffective pollinators, and increasing visit quantity could not compensate for inferior visit quality. Indeed, although the effect was not statistically significant, increased honey bee visits had a marginally negative impact on seed production. Thus, honey bee introductions may erode longstanding plant‐pollinator mutualisms, with negative consequences for plant reproduction. Our study calls for a more thorough understanding of the indirect effects of species introductions and more careful coordination of hive placements. [ABSTRACT FROM AUTHOR]

Insects provide key pollination services in most terrestrial biomes, but this service depends on a multistep interaction between insect and plant. An insect needs to visit a flower, receive pollen from the anthers, move to another conspecific flower, and finally deposit the pollen on a receptive stigma. Each of these steps may be affected by climate change, and focusing on only one of them (e.g., flower visitation) may miss important signals of change in service provision. In this study, we combine data on visitation, pollen transport, and single‐visit pollen deposition to estimate functional outcomes in the high Arctic plant‐pollinator network of Zackenberg, Northeast Greenland, a model system for global warming–associated impacts in pollination services. Over two decades of rapid climate warming, we sampled the network repeatedly: in 1996, 1997, 2010, 2011, and 2016. Although the flowering plant and insect communities and their interactions varied substantially between years, as expected based on highly variable Arctic weather, there was no detectable directional change in either the structure of flower‐visitor networks or estimated pollen deposition. For flower‐visitor networks compiled over a single week, species phenologies caused major within‐year variation in network structure despite consistency across years. Weekly networks for the middle of the flowering season emerged as especially important because most pollination service can be expected to be provided by these large, highly nested networks. Our findings suggest that pollination ecosystem service in the high Arctic is remarkably resilient. This resilience may reflect the plasticity of Arctic biota as an adaptation to extreme and unpredictable weather. However, most pollination service was contributed by relatively few fly taxa (Diptera: Spilogona sanctipauli and Drymeia segnis [Muscidae] and species of Rhamphomyia [Empididae]). If these key pollinators are negatively affected by climate change, network structure and the pollination service that depends on it would be seriously compromised. [ABSTRACT FROM AUTHOR]

• Managing pollination services requires specific targets to maximize production. • Protocols for hive management in crops are not based on ecological knowledge. • Quality of beehive for crop pollination affects productivity and optimal colonies ha−1. • Maximizing blueberry production requires 7 high-quality honeybee hives ha−1. • Reaching similar levels of production with low-quality hives requires 20 colonies ha−1. Animal pollination is essential to guarantee the economic viability of pollination-dependent crops, and honeybees (Apis mellifera L.) play a central role as the most used species worldwide for pollination service management. Despite its importance, recommendations on honeybee hive stocking density are based on rules of thumb that assume hives as standardized units and do not consider the contingencies of the crop's pollen deposition demand. We developed a mechanistic simulation model to assess the consequences of variant hive quality and stocking density scenarios for blueberry productivity per hectare. To do so, we used Bayesian models, field experiments and secondary information to parametrize the simulation and estimate flower visitation rate, pollen deposition, and fruit production at the crop level. We found that maximizing pollen deposition at the crop level can be achieved with seven high quality-hives ha−1 (20000 bees colony−1), whereas reaching similar levels of pollination with conventional hives (10000 bees colony−1) would require 20 hives ha−1. Also, optimal hive stocking densities to maximize blueberry yield ha−1 needs four high quality-hives ha−1, whilst similar levels of productivity could be reached with 20 conventional colonies ha−1. From an economic and productive perspective, a lower unit rental price for conventional hives compensates for the use of less, but more expensive, high quality hives. Therefore, deciding using either low or high-quality hives should be based on, for instance, the logistic implications of using ∼2.5 more hives ha−1 and the consequences of using colonies with a poorer sanitation state for pollination service stability. Our work set the basis for a more biological and evidence-based protocol for honeybee hive management in blueberry crops. Indeed, integrating honeybee and blueberry pollination ecology, we provide a pragmatic approach to maximize crop productivity based on the minimum beehive stocking densities that optimize pollen deposition and crop yield ha−1 depending on hive's quality. Knowing such a minimum allows for reduced operation costs for farmers, lower uncertainty of pollinators contribution to crop productivity and the risk of undesirable pollination scenarios, and helps to limit the potential negative impacts of saturating ecosystems with honeybees. [ABSTRACT FROM AUTHOR]

Background: The frequency and intensity of droughts are expected to increase under global change, driven by anthropogenic climate change and water diversion. Precipitation is expected to become more episodic under climate change, with longer and warmer dry spells, although some areas might become wetter. Diversion of freshwater from lakes and rivers and groundwater pumping for irrigation of agricultural fields are lowering water availability to wild plant populations, increasing the frequency and intensity of drought. Given the importance of seasonal changes and extremes in soil moisture to influence plant reproduction, and because the majority of plants are flowering plants and most of them depend on pollinators for seed production, this review focuses on the consequences of drought on different aspects of reproduction in animal-pollinated angiosperms, emphasizing interactions among drought, flowering and pollination., Scope: Visual and olfactory traits play crucial roles in attracting pollinators. Drought-induced floral changes can influence pollinator attraction and visitation, together with pollinator networks and flowering phenology, with subsequent effects on plant reproduction. Here, we review how drought influences these different aspects of plant reproduction. We identify knowledge gaps and highlight areas that would benefit from additional research., Conclusions: Visual and olfactory traits are affected by drought, but their phenotypic responses can vary with floral sex, plant sex, population and species. Ample phenotypic plasticity to drought exists for these traits, providing an ability for a rapid response to a change in drought frequency and intensity engendered by global change. The impact of these drought-induced changes in floral traits on pollinator attraction, pollen deposition and plant reproductive success does not show a clear pattern. Drought affects the structure of plant-pollinator networks and can modify plant phenology. The impact of drought on plant reproduction is not always negative, and we need to identify plant characteristics associated with these more positive responses., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Premise: Floral orientation is central to plant–pollinator interactions and is commonly associated with floral symmetry. Bilaterally symmetrical flowers are often oriented horizontally for optimal pollinator positioning and pollen transfer efficiency, while the orientation of radially symmetrical flowers is variable. Buzz‐pollinated species (pollinated by vibration‐producing bees) include bilateral, horizontally oriented flowers, and radial, pendant flowers. The effect of floral orientation on pollen transfer has never been tested in buzz‐pollinated species. Methods: Here, we examined the effect of floral orientation on bumblebee‐mediated pollen deposition in three buzz‐pollinated Solanum species with different floral symmetry and natural orientations: S. lycopersicum and S. seaforthianum (radial, pendant), and S. rostratum (bilateral, horizontal). We tested whether orientation affects total stigmatic pollen deposition (both self and outcross pollen) when all flowers have the same orientation (either pendant or horizontal). In a second experiment, we evaluated whether different orientations of donor and recipient flowers affects the receipt of outcross pollen by S. rostratum. Results: For the three Solanum species studied, there was no effect of floral orientation on total pollen deposition (both self and outcross) when flowers shared the same orientation. In contrast, in our experiment with S. rostratum, we found that pendant flowers received fewer outcross‐pollen grains when paired with pendant donors. Conclusions: We suggest that floral orientation influences the quality of pollen transferred, with more outcross pollen transferred to horizontally oriented recipients in the bilaterally symmetrical S. rostratum. Whether other bilaterally symmetrical, buzz‐pollinated flowers also benefit from increased cross‐pollination when presented horizontally remains to be established. [ABSTRACT FROM AUTHOR]

Numerous studies have identified traits associated with anther mimicry; however, the processes underlying floral deception remain poorly documented for these structures. We studied the importance of pollinator attraction and mechanical fit of anther mimics in Tritonia laxifolia (Iridaceae) and their relative contributions to reproductive success. To determine anther mimics role in attraction, we offered bees' binary choices to flowers painted with UV‐absorbent and UV‐reflecting paints. We also conducted preference experiments between flowers with excised anther mimics and unmanipulated controls, from which mechanical fit was assessed by allowing single visits. Anther mimics' effects on female reproductive success were determined using similar treatments, but on rooted plants. Bees preferred UV‐absorbent over UV‐reflecting anther mimics. Bees did not discriminate between flowers with and without three‐dimensional anther mimics. Single visits resulted in more pollen deposition on unmanipulated controls over flowers with their anther mimics excised, which was directly linked to pollen‐collecting behavior. Controls with unmanipulated anther mimics had higher seed set than those with their anther mimics excised. This study provides insights into pollinator‐mediated selection on deceptive floral signals and shows that three‐dimensional anther mimics increases reproductive success through both attraction and pollen‐collecting behaviors. [ABSTRACT FROM AUTHOR]

Open top chambers (OTCs) are a popular method for studying the biological effects of climate change through passive heating, but their effects on biotic interactions are poorly understood, especially for pollination. Here we use the subalpine plants Delphinium nuttallianum and Potentilla pulcherrima to examine the possibility that the effects of OTCs on plant reproduction are not the result of warming but rather OTCs acting as barriers to pollinator movement. Pollinator observations were conducted and stigmas collected from plants inside and outside of OTCs in a meadow in the Rocky Mountains of Colorado, USA. Very few visitors were observed inside of OTCs, which led to severe reductions in visitation rates, by 92% in Delphinium and 85% in Potentilla. The number of conspecific pollen grains on stigmas was 73% lower in OTCs for Delphinium but not Potentilla, likely because it is capable of autogamous self-pollination. This study clearly shows that OTCs can reduce animal pollination, which is also likely to reduce plant reproductive output of outcrossing plants via decreases in the quantity or quality of pollen. OTCs may therefore confound effects of warming on plant reproduction with pollination effects. Although the unintended effects of OTCs on abiotic conditions are well-studied, this study highlights that their effects on biotic interactions require further investigation.

Abstract Pollination services from insects are important for higher yield and better fruit quality in avocado (Persea americana Mill.). Measuring pollinator effectiveness is significant for capturing the relative contributions of different insect taxa to pollination services and for identification of the most important pollinators of this globally important crop. In the present study, we tested pollinator efficiency of avocado in Kenya based on pollen deposition after single visits of flowers by different pollinator species and visitation frequency. We monitored the pollination frequency during the flowering period replicated across six farms. Three trees were selected per farm, each with five flower panicles. Out of the 14 observed insect flower visitor species, pollen deposition efficiency was highest in the Western honey bee (Apis mellifera L.), followed by the hover fly species (Phytomia incisa W.). These two species had both the highest pollen deposition and pollen grain loads on their bodies. Furthermore, A. mellifera was the most frequent avocado flower visitor followed by Diptera except hoverflies. Our results imply that A. mellifera can be managed to achieve adequate pollination services for avocado, particularly in areas lacking efficient wild pollinators.

The lack of pollinators in the oil tree peony field was a serious problem for the seed yield. In the preliminary studies, we found that the seed rate of oil tree peonies was significantly improved by supplementing bees during the flowering stages in the pollination net room. In addition, the performance of Apis mellifera L. was better than Bombus terrestris L. To understand the interaction relationship between flowering characteristics and the managed bees, and the pollen-collecting ability of different species of bees, the flowering traits and the pollen loaded on bees were measured in this study. We found that the bees visited flowers with preference and they prefer to forage the flowers having pollen with higher viability. The B. terrestris carried more pollen (27,000.00 ± 5613.70 grains) on the body surface than that of the A. mellifera (7690.00 ± 2873.26 grains). The A. mellifera outperformed B. terrestris both in pollen deposition per visit on the stigma and on the pollen transfer efficiency. The viability of pollen on the body surface (67.77% ± 19.06%) and hind legs (92.02% ± 10.74%) of A. mellifera were both significantly higher than that of B. terrestris (31.84% ± 4.84% and 83.77% ± 6.40%). Our study indicated that the quantity and quality of pollen loaded on stigma by A. mellifera were both better than B. terrestris, which provided evidence that the A. mellifera was the effective pollinator pollinating for the oil tree peony in the pollination net room.

Context: Landscape simplification is a main driver of insect decline, threatening crop pollination services. Changes in functional features in simplified agroecosystems may impact the abundance of wild pollinators. Objectives: Here, we studied whether different pollinator groups based on life-history are differentially associated to landscape features, and how this affects crop pollination service delivery. Methods: Using window traps in a highly simplified agroecosystem, we surveyed pollinator abundances and diversity associated with: (1) bare fence-lines separating pastures (control), (2) conifer hedgerows (3) farm gardens of diverse exotic plant species (4) effluent-ponds, (5) newly established native-plantings, (6) gorse (Ulex europaeus) hedgerows and (7) open water channels across six to twelve dairy farms. We also measured pollination service delivery to potted pak choi (Brassica rapa) plots near features 1–5 on six farms. Results: Pollinators at gardens, native-plantings, and effluent-ponds delivered significantly more pollination service than at bare fence-lines, with flies being more effective pollinators than bees at all features assessed. Taxa delivering the service also differed across features. The native bee Lasioglossum sordidum delivered more pollination at garden and native-planting features than at other features, drone flies (Eristalis tenax) contributed the majority of pollination service at effluent-ponds and bare fence-lines, while calliphorid flies contributed most pollination at conifer hedgerows. Conclusions: Conversion of functional features to bare fence-lines negatively affects on-farm pollinator diversity and its service to crop plants. However, farmers can benefit from enhancing features containing diverse plant species that support non-bee and bee species proven to deliver measurable crop pollination services. [ABSTRACT FROM AUTHOR]

Floral traits mediate the roles of distinct animals as effective pollinators along a generalization/specialization continuum. Many plant species are visited by different pollinator functional groups and the specific contribution of each group is expected to reflect the set of floral characteristics defined by pollination syndromes. Although considered a highly specialized nectarivorous group, hummingbirds frequently visit flowers lacking apparent specialization to bird pollination. How they contribute to the reproduction of these plants, however, has not been evaluated through field experiments considering multiple non-related plant species simultaneously. Here, we investigated hummingbirds' contributions to the pollination of ten plant species comprising a gradient of adaptation to bird pollination in the Brazilian rupestrian grasslands. We excluded hummingbirds from flowers and evaluated their relative contribution in comparison to insects (mainly bees) on conspecific/heterospecific pollen deposition and fruit set. Floral traits that are typically associated with bird pollination were associated with increased pollen deposition, but not with fruit set in the presence of hummingbirds. With hummingbirds, conspecific and heterospecific pollen deposition increased in most species, while fruit set increased in four plant species with varying degrees of fit to ornithophily. Our results show that assessing the relative contribution of specific pollinator groups may depend on when this contribution is measured, i.e. pollen deposition or fruit set. Considering fruit set, our results indicate that hummingbirds contributed to plant reproduction independently of the fit to bird pollination syndrome. This emphasizes their importance as under-appreciated generalized pollinators in some communities. [ABSTRACT FROM AUTHOR]

Premise of the studyOne proposed function of long styles is to intensify selection among male gametophytes relative to short styles. If so, given sufficient competition, longer styles will have higher rates of pollen tube attrition (failure to reach the style base) within the style than shorter ones. Alternatively, style length may influence pollen receipt, which itself may affect attrition rates.MethodsWe tested these predictions by collecting senescing styles from wild populations of two insect-pollinated Clarkia species. We examined the number of pollen grains adhering to the stigma, length of styles, and rates of attrition from the stigma surface to the stigma-style junction (SSJ), from the SSJ to the style base, and from the stigma surface to the style base. Multivariate analyses estimated the independent effects of pollen grains per stigma, the number of pollen tubes at the SSJ, and style length on attrition.Key resultsStyle length was generally positively correlated with pollen receipt, and the number of pollen grains per stigma was positively correlated with all three attrition rates. In neither species was any attrition rate affected by style length independent of the number of pollen grains per stigma.ConclusionsPollen attrition was mediated by style length, but the function of style length was primarily to increase the number of germinating pollen grains, which affected attrition rates either through stigma clogging or pollen-pollen interactions. Style length may have a direct effect on pollen receipt due to the stigma's position relative to pollinator body parts, but traits correlated with style length may also directly affect pollen receipt.

Premise: Many animals provide ecosystem services in the form of pollination including honeybees, which have become globally dominant floral visitors. A rich literature documents considerable variation in single visit pollination effectiveness, but this literature has yet to be extensively synthesized to address whether honeybees are effective pollinators. Methods: We conducted a hierarchical meta‐analysis of 168 studies and extracted 1564 single visit effectiveness (SVE) measures for 240 plant species. We paired SVE data with visitation frequency data for 69 of these studies. We used these data to ask three questions: (1) Do honeybees (Apis mellifera) and other floral visitors differ in their SVE? (2) To what extent do plant and pollinator attributes predict differences in SVE between honeybees and other visitors? (3) Is there a correlation between visitation frequency and SVE? Results: Honeybees were significantly less effective than the most effective non‐honeybee pollinators but were as effective as the average pollinator. The type of pollinator moderated these effects. Honeybees were less effective compared to the most effective and average bird and bee pollinators but were as effective as other taxa. Visitation frequency and SVE were positively correlated, but this trend was largely driven by data from communities where honeybees were absent. Conclusions: Although high visitation frequencies make honeybees important pollinators, they were less effective than the average bee and rarely the most effective pollinator of the plants they visit. As such, honeybees may be imperfect substitutes for the loss of wild pollinators, and safeguarding pollination will benefit from conservation of non‐honeybee taxa. [ABSTRACT FROM AUTHOR]

The function of the reciprocal position of anthers and stigmas of the floral morphs in distylous flowers is to promote cross-pollination between morphs (legitimate pollination). Deviations from reciprocity can negatively affect the rates of legitimate pollen deposition, but other floral traits or the pollination environment might contribute to the function of distyly. In populations of four species of Palicourea and Psychotria , we quantified reciprocity using adaptive inaccuracy and measured the stigmatic lobe length to estimate how these traits influenced legitimate pollen deposition. We described the functional groups of pollinators and compared legitimate pollen flow between morphs in populations visited by different groups. Variations in reciprocity and stigmatic lobe length correlated with the rates of legitimate pollen depositions, with more reciprocal stigmas and longer stigmatic lobes presenting proportionally more legitimate pollen. Populations most frequently visited by bees or with generalized pollination displayed asymmetries in pollen flow between morphs, but with higher legitimate pollination in the S-morph. In contrast, L- and S-flowers showed similar legitimate pollen deposition in the population predominantly visited by hummingbirds. Our results suggest that reciprocity affects the function of distyly; however, floral traits such as stigmatic lobe length and the pollination environment can also influence the rates of legitimate pollen. [ABSTRACT FROM AUTHOR]

Pollination management for highbush blueberry crops (Vaccinium spp.) generally depends on beehives stocked at variable densities, with little consideration given to optimal pollination levels dictated by the mating system of the crop. This approach limits our capability to accurately forecast the consequences of animal pollination on crop productivity and can result in pollination shortfalls. Using experimental and observational data, we estimated optimal pollination thresholds for blueberry crops that maximize fruit diameter. We manipulated stigmatic pollen loads and used Bayesian models to evaluate the effects on fruit diameter. In this way, we were able to define thresholds for deficient, optimal and supraoptimal pollen deposition in blueberries. These thresholds were then evaluated under field conditions in blueberry farms, and used simulations to estimate the minimum number of honeybee visits required for optimal blueberry pollen deposition. A quadratic relationship described fruit diameter in response to stigmatic pollen load, with optimal pollen deposition peaking at 192 pollen tetrads and ranging between 112 and 274. Our simulations showed that a flower visitation rate guaranteeing, on average, six to seven honeybee visits per flower (i.e. flower visitation rate of 0.6 visits per 100 flowers h−1) would result in 60% of the plant flowers receiving optimum stigmatic pollen deposition. Higher numbers of honeybee visits increased the probability that blueberry stigmatic pollen loads were below the optimum and the probability that smaller berries were produced. We show that adverse pollination scenarios in blueberries can occur through different pathways, either because of a deficit or an excess of pollination that directly impacts the quality of the fruits produced. By identifying thresholds, we provide a pragmatic basis for adaptive management of honeybees based on average visitation rates that are most suitable for growers to manipulate. Our study provides new insights into the mechanisms behind pollination, fruit production, and the contribution of honeybee to blueberry crops. We highlight that systematic pollination management through flower visitation monitoring and clear optimal pollination targets can help prevent detrimental pollination scenarios. [Display omitted] • Pollination shortfall risk blueberry production through different pathways. • Optimal pollen deposition ranges between 112 and 274 pollen grains. • Reaching optimal pollination for highbush blueberry requires 0.6 honeybee floral visits per 100 flower h.−1 • Excess of honeybee visits result in reduced stigmatic pollen loads and production. • Pollination management based on target values can optimize highbush blueberry productivity. [ABSTRACT FROM AUTHOR]

Anthropogenic activity can modify the distribution of species abundance in a community leading to the appearance of new dominant species. While many studies report that an alien plant species which becomes increasingly dominant can change species composition, plant–pollinator network structure and the reproductive output of native plant species, much less is known about native plant species which become dominant in their communities.Euphorbia jolkinii Boissier (Euphorbia, hereafter) has become a dominant native plant in the over‐grazed meadows of Shangri‐La, SW China. During the flowering season of Euphorbia and over 2 years, we quantified the impact of Euphorbia on plant richness and flower visitor richness in 12 subalpine meadows along a gradient of Euphorbia dominance. We also evaluated the floral preferences of flower visitors, interaction evenness of plant–flower visitor networks and the deposition of pollen on the stigmas of two co‐flowering plant species (Gentiana chungtienensis and Anemone rupestris) in each meadow.The species richness of flower visitors to non‐Euphorbia plants was negatively correlated with Euphorbia dominance. As the proportion of Euphorbia increases, flower visitors to Euphorbia decreased, while flower visitors to other co‐flowering plants increased. Interaction evenness decreased as the proportion of Euphorbia increased. Furthermore, the conspecific pollen deposition of one of the two co‐flowering plant species studied, G. chungtienensis, decreased as the proportion of Euphorbia increased.Synthesis. There appears to be little substantive difference between the impact of a newly dominant native plant and the impacts reported for many alien plants on native plant–pollinator communities. This lack of difference suggests that dominance, in addition to plant origin (alien vs. native), could play an important role in influencing the structure and functioning of native communities. This finding has considerable implications for restoration ecology. Thus, communities where natural dominance order has been changed due to anthropogenic activity may not be considered a problem as all the species are native—in reality though, they may be as damaged as communities invaded by alien species. [ABSTRACT FROM AUTHOR]

Many insect species provide essential pollination services. However, the amount of pollen deposited onto a stigma when visiting a flower ('single visit pollen deposition', SVD) can vary greatly among taxa depending on morphological traits of pollinators. Further, SVD is commonly measured using one of two methods ('static': waiting for an insect to visit a flower present on plant, and 'active': removing the flower and presenting it to a flower visitor) that may also differ in their effectiveness.To gain a more comprehensive understanding of how SVD compares among pollinators, we conducted a hierarchical meta‐analysis using data from 28 studies identified by a systematic review. These contained SVD data for 94 bee and 33 fly taxa (hereafter 'wild pollinators'), across 30 plant species from which we included 127 observations. In the analysis of each study, we used the western honey bee Apis mellifera as a comparator species.Wild pollinators deposited more pollen onto stigmas per single visit than honeybees, and those with larger body deposited significantly more pollen than smaller ones. Of the two methodological approaches to assess SVD, 'static' versus 'active', we found no significant difference regarding the amount of deposited pollen.Synthesis and applications. Our meta‐analysis highlights the breadth of wild pollinators that contribute to pollination effectiveness via their delivery of pollen to many crop and non‐crop plant species. However, just 25% of the observations assessed the amount of pollen deposited by fly species. Our findings point to the need to further quantify the pollination effectiveness of non‐bee pollinators as studies have largely focused on managed and wild bee species. [ABSTRACT FROM AUTHOR]

Plants often interact with a wide range of animal floral visitors that can vary in their pollination effectiveness. Flowers of the African sausage tree Kigelia africana are visited by bats and bush babies during the night and by birds during the day. We studied floral traits (phenophases, scent, color, and nectar chemistry) and the visitation frequency and pollination effectiveness of different flower visitors to determine whether K. africana is functionally specialized for bat pollination. We found that flower opening corresponds with bat activity, flowers emit scent dominated by aliphatic esters and alcohols, and that nectar is produced in copious amounts accessible to bats. Pollen deposition on stigmas was twenty‐fold greater per visit by bats than it was per visit by birds, likely a result of the close morphological fit between snouts of bats and the flowers. However, bat visits appear to be rare at some sites and the delayed senescence of flowers that are open throughout the morning provides an opportunity for additional pollination by birds. We conclude that K. africana is primarily adapted for bat pollination, but is also able to exploit other animals for pollination. [ABSTRACT FROM AUTHOR]

Annual pollen accumulation rates of the main tree and shrub taxa of European Russia (Picea, Pinus, Betula, Alnus, Quercus, Tilia, Fraxinus, Ulmus and Corylus), as well as several herbaceous taxa (Poaceae, Cyperaceae, Chenopodiaceae and Artemisia), were obtained using Tauber pollen traps which were placed along a northwest to southeast transect in European Russia. The work was carried out within the framework of the Pollen Monitoring Programme (PMP). The data were analysed using both traditional interpretations of PAR (pollen accumulation rate) values and numerical methods (linear regressions and canonical correspondence analysis, CCA). The various vegetation zones: broadleaved-coniferous forest, broadleaved forest and forest-steppe, differ from each other by the absolute pollen values (PARs) of forest-forming taxa and several wind-pollinated herbs. However, no statistical support for zonal differentiation based on these PARs has been found. The only obvious difference was observed between the forest zone and the forest-steppe. The climatic gradient along the NW–SE transect is reflected by changes in pollen values, but is smoothed due to human influence during past centuries and as a consequence of the dominance of secondary vegetation formations. The highest total PAR, as well as PARs of all the forest-forming taxa, was observed in the southern part of the mixed broadleaved-coniferous forest zone (RU-ZV). The PARs of thermophilic taxa (Tilia, Fraxinus, Acer, Ulmus, Quercus and Corylus), as well as of Picea correspond to warmth availability which is under the influence of a combination of latitude, continentality of climate and microclimatic conditions. According to linear regressions, Picea, Tilia, Quercus and Corylus PARs correspond to Tjul, the July temperature of the previous season. Canonical correspondence analysis indicates that temperature, in particular Tjul, is the main climatic parameter controlling the variation of modern pollen rain. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

1. Measurements of pollinator performance are crucial to pollination studies, enabling researchers to quantify the relative value of different pollinator species to plant reproduction. One of the most widely employed measures of pollinator performance is single‐visit pollen deposition, the number of conspecific pollen grains deposited to a stigma after one pollinator visit. To ensure a pollen‐free stigma, experimenters must first bag flowers before exposing them to a pollinator. 2. Bagging flowers, however, may unintentionally manipulate floral characteristics to which pollinators respond. In this study, we quantified the effect of bagging on nectar volume in watermelon (Citrullus lanatus) flowers, and how this affects pollinator performance and behaviour. 3. Experimental bagging resulted in roughly 30‐fold increases in nectar volume relative to unmanipulated, open‐pollinated field flowers after only a few hours. Honey bees, but not native bees, consistently displayed elevated handling times and single‐visit pollen deposition on unmanipulated bagged flowers relative to those from which we removed nectar to mimic volumes in open‐pollinated flowers. 4. Furthermore, we identify specific bee foraging behaviours during a floral visit that account for differences in pollen deposition, and how these differ between honey bees and native bees. 5. Our findings suggest that experimental bagging of flowers, without accounting for artificially accumulated nectar, can lead to biased estimates of pollinator performance in pollinator taxa that respond strongly to nectar volume. We advise that pollination studies be attentive to nectar secretion dynamics in their focal plant species to ensure unbiased estimates of pollinator performance across multiple pollinator species. [ABSTRACT FROM AUTHOR]

Plant–pollinator network studies have uncovered important generalities in the structure of these communities, rapidly advancing our understanding of the underlying drivers of such a structure. In spite of this, however, it is still unclear how changes in structural network properties influence overall plant pollination success. One key limitation is the lack of information on the relationship between network structural properties and aspects of pollination and plant reproductive success. Here, we estimate four plant species network structural metrics (interaction strength, weighted degree, closeness centrality, and specialization level), commonly used to describe their importance within plant–pollinator networks, at two different sites, and evaluate their effects on pollen deposition and pollen tube success. We found a positive effect of plant–pollinator specialization and a negative effect of closeness centrality on heterospecific pollen load size. We also found a marginal negative effect of closeness centrality on pollen tube success. Our results suggest that increasing plant–pollinator specialization within nested communities (pollinated by one or very few generalist insect species) may result in high levels of heterospecific pollen transfer. Furthermore, the differential effects of plant–pollinator network metrics on pollination success (pollen receipt and pollen tube success), highlight the need to integrate quantity (e.g. visitation rate) and quality (e.g. pollen delivery) aspects of pollination to achieve a more mechanistic understanding of the relationship between plant–pollinator network structure and function. Such knowledge is key to evaluate the resilience and stability of plant–pollinator communities and the services they provide in the face of increasing human disturbances. [ABSTRACT FROM AUTHOR]

Background Despite Stebbins' principle of the most efficient pollinator being proposed decades ago, the most important pollinators are still mainly identified using the frequency of visits to flowers. This shortcoming results in a gap between the characterization of the flower visitors of a plant species and a reliable estimation of the plant fitness consequences of the mutualistic interaction. The performance of a mutualistic visitor depends on its abundance, behaviour, effectiveness (pollen removal and deposition per unit time) and efficiency (seed set per unit time) conditioned by the temporal matching between pollinator activity and temporal patterns of maturation of the sexual functions of flowers. Although there have been recent attempts to provide a conceptual and methodological framework to characterize pollinators' performance, few have combined all key elements of visitors and plants to provide an accurate estimation of pollinators' performance under natural conditions. Methods We complement information on the flower biology and mating system of the sub-shrub Lepechinia floribunda (Lamiaceae) to provide a daily quantitative estimation of performance (effectiveness and efficiency) of the more abundant pollinators, i.e. native bumble-bees (Bombus spp.) and leafcutter bees (Megachile sp.), and the exotic honey-bee (Apis mellifera). Key Results Unlike honey-bees or leafcutter bees, native bumble-bees matched the daily pattern of nectar production and stigma receptivity, and showed higher effectiveness and efficiency. Despite the overabundance of honey-bees, visits occurred mainly when stigmas were not receptive, thus reducing the honey-bees' overall performance. Conclusions Bumble-bees appear to be the most important pollinators and potential historical mediators of reproductive trait evolution in L. floribunda. Because the production of seeds by bumble-bees involved fewer pollen grains for plants and less investment in floral display than honey-bees, contemporary and expected changes in pollinator abundance may affect future L. floribunda floral evolution. If bumble-bees were to be further displaced by anthropogenic disturbance or by competition with honey-bees, their lower efficiency will select for a larger floral display increasing reproductive costs. This scenario may also impose selection to reduce dichogamy to match honey-bee foraging activity. [ABSTRACT FROM AUTHOR]

The study by Barahona-Segovia et al. (2023) examines the influence of edge effect, landscape composition, and local characteristics on non-bee flower visitors in apple orchards. While their article improves our understanding of ecosystem dynamics in agricultural landscapes, it has important limitations regarding the importance of non-flower visitors as pollinators and their ability to compensate for declines in wild bee populations. The study does not address the distinction between flower visitors and true pollinators, relying on indirect measures such as contact with flower reproductive parts and visitation rate as proxies for pollinator effectiveness. Therefore, the authors fail to measure the basic definition of pollination: the act of transferring pollen grains from the anther to the stigma of a flower. Thus, the methodology used and the results of the study do not support the effectiveness of non-bees as pollinators compared to wild bees. The authors should have been cautions in extrapolating the conclusions of their study for orchard management strategies. Further studies with solid evidence are needed to quantify the contribution of non-bee pollinators to crop pollination and to allow a fair comparison between bees and non-bee visitors. • Barahona-Segovia et al. (2023) study the influence of edge effect and landscape composition on non-bee flower visitors in apple orchards. • The study lacks evidence that non-bee visitors can effectively keep the pollination delivered by wild bee populations. • Caution is necessary when interpreting the study's findings and applying them to crop ecosystem management. • Direct measures of pollinator performance, such as pollen deposition, should be included in future studies. [ABSTRACT FROM AUTHOR]

Grass pollen allergy is widespread all around the globe. With an increasing number of people living in cities, the examination of grass pollen levels within cities and their surroundings has increased in importance. The aim of this study was to examine different temporal and spatial scales of grass pollen concentration and deposition across urban and semi-rural environments in the years 2019 and 2020. We installed different types of pollen traps in the city of Ingolstadt (Bavaria, Germany) and its surroundings: volumetric pollen traps at roof level to assess background pollen concentration and gravimetric pollen traps and portable volumetric traps at street level. We considered grass pollen concentration and deposition in the context of land use and management. Our data showed that the grass pollen season in 2020 was longer and more intense than in 2019. Background grass pollen concentration was generally higher at the semi-rural site in both years: peak values were eight times (2019) and more than four times (2020) higher, and Seasonal Pollen Index was more than four times and almost three times higher in 2019 and 2020, respectively. Analyses of spatial variations measured at street level revealed higher numbers for pollen deposition and concentrations at semi-rural than at urban sites. Recorded values were linked to local vegetation and the management of grass areas surrounding the traps. Analyses of diurnal variations at street level in June 2019 showed that pollen concentration for all sites, independent of their degree of urbanization, were highest at noon (22.2 pollen grains/m³ vs. 8.5 pollen grains/m³ in the morning and 10.4 pollen grains/m³ in the evening). Diurnal variations at roof level showed similarities for the same days but differed when considering the whole season. Our data suggest the importance of the management of grass areas as areas cut earlier have a decreased amount of emitted pollen.

Co‐flowering plants may commonly experience interspecific pollination. It remains unknown, however, whether interspecific pollination is a largely stochastic process or consistent enough over years to exert selection for traits that can reduce interspecific pollination or ameliorate its deleterious effects on reproduction. To assess the likelihood of this precondition being met, stigmatic pollen loads on 17–34 insect‐pollinated plant species over three consecutive years were scored in a subalpine meadow in southwestern China. Plant species varied significantly in the amount and proportion of heterospecific pollen (HP) on stigmas. Both the number of HP species and the proportion of the pollen load that was HP for each recipient species correlated positively between years (reflected in pairwise correlations for all year‐by‐year combinations). Although inter‐annual variation was smaller for conspecific pollen (CP) than for HP loads, species tended to experience either consistently high or consistently low HP proportions across years. We found that species with higher stigmatic HP proportions generally experienced lower proportional variation in stigmatic HP, an unexpected result if high HP loads are the result of rare stochastic events. The novel finding of between‐year consistency in stigmatic loads of heterospecific pollen suggests that adaption to stigmatic loads of HP is possible, and two divergent strategies may have evolved: HP avoidance and HP tolerance. The observation of temporally consistent differences among species in levels of HP supports the idea that natural selection may be operating either to increase tolerance or to minimize arrival of heterospecific pollen on stigmas in co‐flowering plants. Such adaptations may be important for the maintenance of high levels of local plant diversity in biodiversity hotspots such as our study area. [ABSTRACT FROM AUTHOR]

Most angiosperms rely on animal pollination for reproduction, but the dependence on specific pollinator groups varies greatly between species and localities. Notably, such dependence may be influenced by both floral traits and environmental conditions. Despite its importance, their joint contribution has rarely been studied at the assemblage level.At two elevations on the Caribbean island of Dominica, we measured the floral traits and the relative contributions of insects versus hummingbirds as pollinators of plants in the Rubiaceae family. Pollinator importance was measured as visitation rate (VR) and single visit pollen deposition (SVD), which were combined to assess overall pollinator effectiveness (PE).In the wet and cool Dominican highland, we found that hummingbirds were relatively more frequent and effective pollinators than insects, whereas insects and hummingbirds were equally frequent and effective pollinators at the warmer and less rainy midelevation. Furthermore, floral traits correlated independently of environment with the relative importance of pollinators, hummingbirds being more important in plant species having flowers with long and wide corollas producing higher volumes of dilute nectar.Our findings show that both environmental conditions and floral traits influence whether insects or hummingbirds are the most important pollinators of plants in the Rubiaceae family, highlighting the complexity of plant–pollinator systems. [ABSTRACT FROM AUTHOR]

Pumpkins and winter squash require insect pollination to set fruit, but only three bee species are important pollinators of these crops in the Northeastern US. To determine if natural levels of pollen deposition are sufficient for full fruit production, open pollination was measured by counting pollen grains on stigmas, and open pollination was compared to supplemental hand pollination for fruit set, fruit size, and seed number. A threshold of 2300 pollen grains per stigma was sufficient for full pollination and fruit production. This threshold was met in 79 out of 80 combinations of site and sample date over four years on farms across Connecticut with a wide range of field sizes and pest management practices. Along with stigma collection, bees per flower were counted hourly on 100 flowers along a transect. Counts of bumble bees on female flowers were more closely related to the amount of pollen deposited than counts of bees on all flowers or counts of honey bees or squash bees on female flowers. There was tremendous variation in abundance of the three bee species on female flowers across farms within a year and even among years on a single farm.

Staminodes are sterile stamens that produce no pollen, exhibit diverse structures and perform various functions. Flowers of Phanera yunnanensis possess three fertile stamens with large anthers and long filaments, and seven staminodes with tiny anthers and short filaments. To investigate the adaptive significance of staminodes in this species, we studied effects of staminode removal on pollen removal and deposition, flower visitation rate and fruit set in Xishuangbanna, south-western China. Four species of nectar-foraging pollinators visited flowers, mostly Amegilla zonata and Apis cerana (2.80 ± 0.15 and 1.76 ± 0.41 visits h−1 per flower, respectively). Staminode removal did not affect fruit set, but increased visitation by A. cerana by 2.6-fold, reduced visitation by A. zonata by 68% and increased the pollen removal rate for both pollinators (all effects were significant). Staminode removal significantly reduced pollen deposition rate for A. zonata , but not for A. cerana. These results suggest that the staminodes of P. yunnanensis filter which insects act as pollinators and affect pollen removal and deposition rates. By reducing pollen removal rates, staminodes may implement a pollen-dispensing schedule that spreads pollen dispersal from individual flowers over multiple pollinators. By altering pollen deposition rates, staminodes may influence reproductive fitness in other ways. [ABSTRACT FROM AUTHOR]

For many years, we have observed a significant rise in urban population, the spatial development of cities, and an increase in urbanized areas. More and more people feel the need to have contact with nature. The interest in forest recreation is growing, though the forest is a serious source of allergenic plant pollen. The aim of the present study was to compare two forest types in the context of their recreational potential and the effect strength of aeroallergens. This study was conducted in SE Poland in a Nemoral Scots pine forest (RB) and in a Central European submountainous beech forest (TH). Their recreational potential was assessed. Samples of moss containing plant pollen were collected under the canopy, from forest clearings and forest edges as well as in an open area. Based on the number of pollen grains deposited in moss pollsters, the forest impact on humans was calculated. The recreational potential values for both sites studied are evidence of the high recreational suitability of these forests, but the recreational capacity of RB is lower compared to TH. Palynological analysis showed that the pollen deposition is higher in BR and that the plant pollen risk is lowest under the canopy, regardless of the forest type. The beech forest was found to be characterized by greater recreational potential and a weaker actual effect of pollen allergens than the pine forest. In assessing forest recreational potential, palynological data should form the basis for modification of the degree of recreational suitability. Such information would also be useful in controlling recreational traffic since, as we have proved, visiting appropriate places in a forest allows the exposure of allergen sensitive people to be reduced. [ABSTRACT FROM AUTHOR]