Pollinator Visitation Rates Research Articles

Insect Pollination, More than Plant Nutrition, Determines Yield Quantity and Quality in Apple and Pear.

Agricultural yield is the result of multiple factors and ecological processes (e.g., pollination, fertilization, pest control). Understanding how the different factors interact is fundamental to designing management practices aimed to increase these yields, which are environmental friendly and sustainable over time. In this study, we focus on insect pollination and plant nutrition status, since they are two key factors that influence crop yield. The study was carried out in Northwest Patagonia Argentina, which is an area of intensive production of pears and apples of global importance, during the harvest seasons 2018 and 2019. The plant nutrition was estimated from leaf chlorophyll content. Biotic pollination benefits were evaluated by comparing fruit quantity (fruit to flower ratio) and quality (weight, size, and sugar concentration) from approximately 25 flowers exposed to pollinators and 25 flowers excluded to them per tree (a total of 160 apple trees and 130 pear trees). In addition, we estimated the visitation rate of pollinators to flowers and related it to fruit quality in apple. Despite different floral characteristics, we found in both crops a positive effect of insect pollination in both the quantity and the quality of the fruits. Interestingly, the nutrition of the trees, although variable, did not affect either the quantity or the quality of the fruits. Despite the weak effect of nutrition, we found no interaction between pollination and plant nutrition (i.e., additive effects). These results highlight the importance of agricultural practices that promote pollinators on farms.

Pollinator visitation rate and effectiveness vary with flowering phenology.

Flowering time may influence pollination success and seed set through a variety of mechanisms, including seasonal changes in total pollinator visitation or the composition and effectiveness of pollinator visitors. We investigated mechanisms by which changes in flowering phenology influence pollination and reproductive success of Mertensia ciliata (Boraginaceae). We manipulated flowering onset of potted plants and assessed the frequency and composition of pollinator visitors, as well as seed set. We tested whether floral visitors differed in their effectiveness as pollinators by measuring pollen receipt and seed set resulting from single visits to virgin flowers. Despite a five-fold decrease in pollinator visitation over four weeks, we detected no significant difference in seed set among plants blooming at different times. On a per-visit basis, each bumblebee transferred more conspecific pollen than did a solitary bee or a fly. The proportion of visits by bumblebees increased over the season, countering the decrease in visitation rate so that flowering time had little net effect on seed set. This work illustrates the need to consider pollinator effectiveness, along with changes in pollinator visitation and species composition to understand the mechanisms by which phenology affects levels of pollination.

Natural selection on flower size in invasive Cytisus scoparius along an elevation gradient

AbstractAimsEstablished invasive plant species have more diverse gene pools than single populations in their home range. This genetic and often phenotypic variation allows for natural selection to act and produce rapid adaptations as an invasive species interacts with other members of the community. For an invasive flowering plant, interactions with pollinators may lead to adaptations to a heterogeneous pollinator community. The variation in the pollinator community in the invaded range is similar to variation in the native range, suggesting that adaptations may mirror patterns seen in the home range. In this study, we investigated variation in flower size in Cytisus scoparius, an invasive leguminous shrub, along an elevation gradient.MethodsThis study took place in the Capitol State Forest in Washington State. We measured flower widths and the proportion of visited flowers, using 10 plants per field site. Sites were located along an elevation gradient and were visited three times to measure phenological variation on a per-plant basis.Important FindingsWe saw positive selection for flower size, albeit without a distinct pattern of higher selection at higher elevations. The pattern of natural selection could be seen both in terms of pollinator visitation rates and in seed production. We also found that the largest contributor to changes in seed production was not elevation or flower size but management practices.

The factors influencing the pollinators visitation of the oilseed rape cultivars

Currently, the hybrid cultivars are predominant in the cultivation of winter oilseed rape in Europe. Cultivation of hybrid cultivars instead of the traditional line can affect the visitation of pollinators. Beekeepers and farmers claim that hybrid cultivars are not visited by pollinators as much as the line. Ten yellow and one white flowering oilseed rape cultivars were used to compare the visitation rates of pollinators (Apis mellifera L. and Bombus sp.) during flowering in the years 2015–2017. At the same time, the visitation of hybrid and line cultivars by pollinators was evaluated. Visitation of pollinators on each cultivar was calculated from observed visitations to flowering oilseed rape plants in an area 2.1 m<sup>2</sup> from the edge of single plots for 20 s. The results from this study clearly show that the individual cultivars, whether hybrids or lines, did not have a major influence on the pollinators’ visitation, either by honey bees or bumble bees. It is thus proved that hybrid cultivars do not affect the pollinator visitation and there is no need to worry about the prevalence of these cultivars in the Czech fields. However, a more significant effect for both pollinator groups appears to have been the color of the flower.

Effects of invasive Cirsium arvense on pollination in a southern Appalachian floral community vary with spatial scale and floral symmetry

Invasive plants can alter pollination dynamics by disrupting pollinator visitation and pollen transfer dynamics. However, a consensus regarding the direction of their overall effects (competitive vs. facilitative) remains elusive. Here, we evaluate the role of floral traits and spatial scale (community vs. floral neighborhood) in mediating invasive Cirsium arvense effects on resident plant species at multiple stages of the pollination process. C. arvense decreased pollinator visitation rate at the community level only for species with radial floral symmetry. At the floral neighborhood scale, pollinator visitation rate to all resident species was lower in the presence of C. arvense regardless of symmetry. C. arvense altered patterns of conspecific pollen receipt at the floral neighborhood scale, but the direction of the effect varied by plant species. We argue that these scale-dependent effects may be mediated by differences in foraging range and behavior of the main pollinators in the community. C. arvense, however, did not affect the overall reproductive success of resident species at either scale, suggesting that plants at our study sites may not be pollen limited. We further show evidence suggesting that C. arvense may alter the structure of community-level plant–plant interactions via heterospecific pollen transfer by subverting the roles of resident pollen donors within the pollen transfer network. Overall, our results suggest that generalized species (with radial flowers) may be more susceptible to invasive species’ effects than specialized ones (bilateral flowers) and highlight the need to consider scale-dependent effects in order to develop a more predictive understanding of invasive species effects in nature.

Floral structures affect on pollination events of sandalwood in four landraces along landscape gradients in Gunung Sewu, Java, Indonesia

Sandalwood, one of the most economic-endangered species, was the origin to the south-eastern islands of Indonesia, but is recently existed as new landraces in several community forests in Gunung Sewu Geopark, Indonesia. All of landraces consisted of three floral variants (YBF, refers to “yellow big flower”; RBF, “red big flower”; and RSF, “red small flower”, respectively). Our previous findings reported differences on floral structures among variants. In this study we further analyzed these variants differences and its consequence on pollination events, among four landraces represented each geographical zone in Gunung Sewu Geopark, in the 2016 flowering periods. The flowering traits of each variant and landrace were measured. Floral visitors diversity, visitation rate and pollination behaviour were observed in each of population and floral variants. Results showed that flower abundance, visitor diversity and visitor abundance varied with sites but were similar among floral variants. Flowers abundance was strongly correlated to the pollinator visitation rate. Visitors diversity varied with sites due to the differences on flower abundance, environmental condition and altitude. The cooler and wetter site was visited more by Dipterans and Hymenopterans. The warmer, drier and lower sites were visited more by Lepidopterans and Dipterans. Sites with fewer flowers received less visitor diversity and abundance. Visitors preference to a given floral variant might be attributed to the differences on floral structures, sizes and colors. Lepidopterans belong to the moth groups (Arctiidae, Hesperiidae and Noctuiidae) preferred to visit the yellow flowers of YBF variant, while those belong to the butterflies groups (Papillionidae, Nymphalidae and Pieridae) preferred the red flowers of RBF and RSF. All six families of Hymenopterans preferred to visit the red flowers with bigger size, RBF. In contrast, all four families of Coleopterans, as well as the four families of Hemipterans, preferred the yellow flowers of YBF. All four families of Dipterans made similar visits to both RBF and YBF which have bigger flowers, while the visitation was less in RSF.

Sharing of pollinators between the invasive Taraxacum officinale and co-flowering natives is not related to floral similarity in the high-Andes

Non-native plant species with a taxonomic affinity to co-occurring natives may perform best as invaders into plant-pollinator networks because their similarity in floral morphologies with natives enabled them to co-opt their pollinators. However, non-native species may impact the reproduction of natives by altering their pollination only if they share pollinators and if natives depend on pollinators for seed-set, premises that are often assumed but seldom tested. The non-native invasive species Taraxacum officinale (Asteraceae) co-exist and co-flower with other asteraceous species in the high elevation of the central Chilean Andes. In this study we determined the dependence on pollinators for seed-set in five co-occurring and co-flowering native asteraceous species and assessed the similarity in insect pollinators between the non-native and this five native species that differ in their floral similarity with the former species. Pollinator exclusion experiments were performed to determine the dependence of pollinators for seed-set in the native species. Characteristics such as capitula size and colour were measured to quantitatively assess the similarity in the floral morphology between T. officinale and the native species. The identity and visitation rates of insect pollinators that visit T. officinale and the five native species were determined. Native species were highly dependent on the transport of pollen by insects to produce seeds. T. officinale shared a moderate to high proportion (34–94%) of insect pollinators with the five asteraceous native species studied, but the level of overlap in pollinators was not related with the floral similarity between the non-native and the native species. The presence of the non-native species T. officinale has the potential to alter the pollinator services to co-flowering native species in the Andes of central Chile, with no higher impacts on those species with the most similar flowers.

Floral Longevity and Attraction of Arctic Lupine, Lupinus arcticus: Implications for Pollination Efficiency

Pollination by insects is a mutualistic relationship in which flowers receive pollen for reproduction while pollinators are rewarded with pollen or nectar. Floral longevity (the period an individual flower blooms) and floral attraction (the period during which pollinators are attracted to the flower, often indicated by petal colour) both play prominent roles in plant and pollinator success. This study investigated whether floral longevity and floral attraction were mediated by pollination type in arctic lupine (Lupinus arcticus S. Wats.), a common herbaceous perennial in northwestern North America. Flowers were either open to pollinators, cross-pollinated by hand, or bagged to prevent cross-pollination, and floral longevity, seed set, and flower colour were observed. Open and hand-pollinated flowers had significantly shorter floral longevities and higher percent fruit sets than bagged flowers. A colour change of the banner petal marking from white to pink occurred in some flowers and was a signal of floral attraction, as pollinators preferentially visited pre-change flowers. Pre-change flowers contained more pollen and were less likely to have been injured by herbivory than post-change flowers, yet the colour change was not related to pollination type or fruit set. Pollination-induced shortening of floral longevity is likely an adaptation to limited plant resources and pollinator visitation rates. For L. arcticus, this could be influenced by short growing seasons and low annual temperatures in the study area. In the face of climatic changes and shifting species phenologies, the mediation of floral longevity by pollinators could decrease temporal mismatch between plants and their pollinators, yet the many factors at play make this difficult to accurately predict.

Wild pollinator activity negatively related to honey bee colony densities in urban context.

As pollinator decline is increasingly reported in natural and agricultural environments, cities are perceived as shelters for pollinators because of low pesticide exposure and high floral diversity throughout the year. This has led to the development of environmental policies supporting pollinators in urban areas. However, policies are often restricted to the promotion of honey bee colony installations, which resulted in a strong increase in apiary numbers in cities. Recently, competition for floral resources between wild pollinators and honey bees has been highlighted in semi-natural contexts, but whether urban beekeeping could impact wild pollinators remains unknown. Here, we show that in the city of Paris (France), wild pollinator visitation rates are negatively correlated to honey bee colony densities present in the surrounding landscape (500m –slope = -0.614; p = 0.001 –and 1000m –slope = -0.489; p = 0.005). Regarding the morphological groups of wild pollinators, large solitary bee and beetle visitation rates were negatively affected by honey bee colony densities within a 500m buffer (slope = -0.425, p = 0.007 and slope = - 0.671, p = 0.002, respectively) and bumblebee visitation rates were negatively affected by honey bee colony density within a 1000m buffer (slope = - 0.451, p = 0.012). Further, lower interaction evenness in plant-pollinator networks was observed with high honey bee colony density within a 1000m buffer (slope = -0.487, p = 0.008). Finally, honey bees tended to focus their foraging activity on managed rather than wild plant species (student t-test, p = 0.001) whereas wild pollinators equally visited managed and wild species. We advocate responsible practices mitigating the introduction of high density of honey bee colonies in urban environments. Further studies are however needed to deepen our knowledge about the potential negative interactions between wild and domesticated pollinators.

Degree of fragmentation and population size do not adversely affect reproductive success of a rare shrub species, Banksia nivea (Proteaceae), in a naturally fragmented community

Abstract Fragmentation of plant communities is generally considered to be detrimental to the survival of the constituent species, especially those that are rare. We investigated the effects of fragmentation on reproductive biology in nine populations of the rare taxon Banksia nivea subsp. uliginosa, differing in size and habitat context. Small mammals were the main pollinator, with lower contributions from honeybees and birds (honeyeaters). There was no significant relationship between population size, fruit set and seed germinability. Fruit set was marginally highest (25.5 ± 3.4) in medium size populations and was variable over years. Lower fruit set (1.0 ± 0.6) in the smallest population may be due to inbreeding depression or lack of pollinators in a degraded habitat, but low fruit set was also observed in the largest population despite high levels of gene flow, possibly due to low pollinator visitation rate in a low-density population. Seeds from all populations had high germination success (>93.4%). Predation occurred in up to 56% of fruit and increased with increasing population size, but was not significantly different between populations of different size. Our study provided evidence that the reproductive output in species in a naturally fragmented landscape system may be resilient to reduced population size and other influences of anthropogenic fragmentation.

Impact of floral characters, pollen limitation, and pollinator visitation on pollination success in different populations of Caragana korshinskii Kom

Caragana korshinskii Kom. has a significant function in desert-grassland revegetation in arid regions. Plant reproduction in arid regions can be restricted due to inadequate pollen receipt and reduced pollen transfer. An assessment of pollination success as a result of pollen limitation and pollinator visitation in various C. korshinskii populations is presently lacking. We thus tested three different treatments (pollen addition, control, and procedural control) to elucidate how pollen limitation affects seed numbers per flower in C. korshinskii. We also determined the effect of pollinator visit frequency on seeds per flower. Our results demonstrated that there was a higher proportion of open flowers and mature fruits in the managed population than in the natural population. Pollen addition significantly increased seed number per flower, and pollen limitation was determined to be a significant limiting factor in seed production. Furthermore, Apis mellifera was determined to be the principal pollinator, and pollinator visitation frequency was significantly correlated with open flower number. Our findings also demonstrated that pollinator visitation rate and seed production were positively correlated. Management and pollinator visitation could affect seed production, which may explain the higher seeds per flower in the managed population compared with the natural population.

Spatial variability in a plant–pollinator community across a continuous habitat: high heterogeneity in the face of apparent uniformity

Large‐scale spatial variability in plant–pollinator communities (e.g. along geographic gradients, across different landscapes) is relatively well understood. However, we know much less about how these communities vary at small scales within a uniform landscape. Plants are sessile and highly sensitive to microhabitat conditions, whereas pollinators are highly mobile and, for the most part, display generalist feeding habits. Therefore, we expect plants to show greater spatial variability than pollinators. We analysed the spatial heterogeneity of a community of flowering plants and their pollinators in 40 plots across a 40‐km2area within an uninterrupted Mediterranean scrubland. We recorded 3577 pollinator visits to 49 plant species. The pollinator community (170 species) was strongly dominated by honey bees (71.8% of the visits recorded). Flower and pollinator communities showed similar beta‐diversity, indicating that spatial variability was similar in the two groups. We used path analysis to establish the direct and indirect effects of flower community distribution and honey bee visitation rate (a measure of the use of floral resources by this species) on the spatial distribution of the pollinator community. Wild pollinator abundance was positively related to flower abundance. Wild pollinator visitation rate was negatively related to flower abundance, suggesting that floral resources were not limiting. Pollinator and flower richness were positively related. Pollinator species composition was weakly related to flower species composition, reflecting the generalist nature of flower–pollinator interactions and the opportunistic nature of pollinator flower choices. Honey bee visitation rate did not affect the distribution of the wild pollinator community. Overall, we show that, in spite of the apparent physiognomic uniformity, both flowers and pollinators display high levels of heterogeneity, resulting in a mosaic of idiosyncratic local communities. Our results provide a measure of the background of intrinsic heterogeneity within a uniform habitat, with potential consequences on low‐scale ecosystem function and microevolutionary patterns.

Contribution of bees and other pollinators to watermelon (Citrullus lanatus Thunb.) pollination

Watermelon (Citrullus lanatus Thunb.) is an important economic crop with 29.6 million tons produced worldwide. However, few native bees and other pollinators have been documented to visit watermelon flowers and the contribution of these insects to watermelon pollination has yet to be determined. We examined 40 commercial watermelon fields from 2013 to 2016 and obtained information on pollinator visitation rates for managed and wild pollinators at different distances from field margins. We determined the amount of pollen on common pollinators’ bodies, how much time these pollinators spent on flowers, and the amount of pollen they deposited on stigmas. Forty-three species of potential pollinators were documented during the 4-year study. Managed honey bees (Apis mellifera L.) were the most common visitor, but numerous other pollinators (e.g., Agapostemon splendens Lepeletier, Campsomeris plumipes var. fossulana Fabricius) were found to be abundant. This sweat bee and scoliid wasp carried as much watermelon pollen as worker A. mellifera did. No differences were detected among visitation rates among various taxonomic groups at different distances (0, 25, 50, 100 m) from field margins except for small bees (e.g., Lasioglossum, Halictus), which were found in higher abundances at the field margins. Managed and wild bumble bees (Bombus spp.) were not common visitors of watermelons and may not be a good surrogate for managed honey bees. Overall, numerous insect species contribute to watermelon pollination. Therefore, watermelon growers should consider future land-use changes or other management practices that might positively affect the abundances of bee and wasp species.

Taxonomic and functional diversity of the co‐flowering community differentially affect Cakile edentula pollination at different spatial scales

Abstract The number of co‐flowering species, floral density and floral trait diversity can be major determinants of pollinator‐mediated plant–plant interactions in a community. However, evaluation of how each one of these co‐flowering components affects the pollination success of a single focal plant species, and how these effects vary at different spatial scales, is lacking. Here, we evaluated the effects of functional diversity (flower morphology and colour), taxonomic diversity (reflecting potential sampling effects) and flower density (conspecific and heterospecific), on the pollinator environment (i.e. visitation rate and pollinator diversity) and pollination success (i.e. pollen load size and number of pollen tubes per style) of Cakile edentula (Brassicaceae). We applied structural equation models (SEMs) at the floral‐neighbourhood (plot level) and community‐wide scales to uncover the factors that mediate co‐flowering community effects on C. edentula pollination success. We found that co‐flowering community effects at the community level are more important than fine‐scale floral‐neighbourhood differences in mediating plant pollination success in our study species. Increasing plant functional diversity decreased pollinator visitation rate but increased the diversity of pollinator functional groups visiting C. edentula flowers. Taxonomic diversity negatively affected pollinator diversity suggesting that other unmeasured floral traits may be relevant or that single‐species effects (sampling effects) may be important. Overall, our results suggest that functional floral trait diversity in a community may be the most important factor influencing pollination success of species in a community. We also found evidence for intra‐ and interspecific pollinator competition mediated by flower density, but none of these effects seemed to have a significant impact on pollination success. This study is an important step towards understanding the complexity of co‐flowering community effects on the pollination success of individual plant species at multiple spatial scales. This study further reveals the potential importance of plant functional diversity in a community in helping predict competitive and facilitative interactions in co‐flowering communities. Synthesis. Floral density and taxonomic and functional co‐flowering diversity are important drivers of pollination success in flowering plants. The effects of the co‐flowering diversity on the pollination success of plant species can largely depend on the spatial scale being studied. Only evaluating the outcomes of pollinator‐mediated plant–plant interactions at multiple stages of the pollination process can lead to a complete understanding of their ecological consequences in nature.

Effect of Pollen Limitation and Pollinator Visitation on Pollination Success of Haloxylon ammodendron (C. A. Mey.) Bunge in Fragmented Habitats.

Haloxylon ammodendron (C. A. Mey.) Bunge is an ecologically important species in arid regions. Pollen limitation may decrease plant reproduction due to low levels of pollen transfer and inadequate pollen receipt. In arid regions, pollen limitations of many plant species may be influenced by habitat fragmentation. However, whether pollen limitation and pollinator visitation affect the pollination success of H. ammodendron (Amaranthaceae) in fragmented habitats still needs further study. In this study, we calculated the pollen limitation in natural and fragmented habitats to estimate the effect of habitat fragmentation on pollen limitation. In different habitats, we investigated the relationship between the number of open flowers and pollinator visiting frequency. In addition, we examined how habitat fragmentation affects pollination success through the influence of pollinator visitation rate on seed set. Our results indicated that pollen limitation was the important limiting factor for seed set in fragmented and natural habitats. The results showed higher pollinator visitation rates resulted in a higher percentage of seeds in both habitats. In H. ammodendron, Apis mellifera was found to be the dominant pollinator. These results may support the assertion that plants evolve traits to attract pollinators and pollinators increase their visiting frequency to better exploit the floral resources. We also determined that outcrossing was dominant in the breeding system and that wind pollination played an important role in pollination success. This study aims to contribute to a better understanding of how environmental heterogeneity affects pollen limitation, pollinator visitation, and pollination success in arid regions.

Number of Pollinators and Its Visitation Rate Incur Different Intensities of Pollen Limitation in Meconopsis integrifolia

Pollen limitation commonly exists in the alpine species, yet, experimental estimates on the changeable trajectory of pollen limitation along elevational changes are rarely. We used field observations and supplemental hand pollination treatment to estimate the variation in pollen limitation among five different altitudes populations (from 3600 m.a.s.l. to 4400 m.a.s.l.) in Meconopsis integrifolia in two consecutive years. Correlation analysis was used to estimate which factor incurred the pollen limitation. Hand supplemental pollination indicated that pollen limitation occurred in the studied populations in both years. Pollen limitation was similar among low-elevation populations but doubled in the highest elevation population (4452 m.a.s.l.). The number of pollinators and visitation rate of pollinators were negatively related to the pollen limitation. Our results indicated that number of pollinators and visitation rate of pollinators were the main factors which incurred variation in pollen limitation of M. integrifolia among different altitudes.

Reproductive assurance weakens pollinator-mediated selection on flower size in an annual mixed-mating species.

In animal-pollinated plants, direct and indirect selection for large and small flowers in predominantly outcrossing and selfing species, respectively, is a common consequence of pollen limitation (PL). However, many hermaphroditic species show a mixed-mating system known as delayed selfing, which provides reproductive assurance (RA) only when outcrossing is not realized. Although RA is expected to reduce pollinator-mediated selection towards larger flowers, the consequences of delayed selfing for selection on flower size in mixed-mating species remain overlooked. We investigated whether RA weakens selection on flower size in Tuberaria guttata, a mixed-mating annual herb. We related pollinator visitation rates to flower size and measured seed production in emasculated, hand cross-pollinated and intact (control) flowers in three natural populations. For each population, we estimated variation in PL and RA across individuals differing in flower size and phenotypic selection on this trait. Pollinator visitation increased and RA decreased with flower size in all populations. Increasing RA diminished but did not fully alleviate PL, because of early-acting inbreeding depression. In the least-visited and most pollen-limited population, RA increased seed production by >200 %, intensely counteracting the strong pollinator-mediated selection for larger corollas. In the most-visited population, however, RA increased seed production by an average of only 9 %. This population exhibited the largest fraction of individuals that showed a decrease in seed production due to selfing and the weakest pollinator-mediated selection on flower size. The results suggest that the balance between the extent of RA and outcrossing contributes to determine flower size in mixed-mating systems. Pollinator-mediated selection favours larger flowers by increasing outcrossed seeds, but the benefits of RA greatly lessen this effect, especially under severe conditions of pollen limitation. Our findings also indicate that a mixed-mating system can represent an 'evolutionary trap' under an adequate pollinator supply.

Nectar yeasts enhance the interaction between Clematis akebioides and its bumblebee pollinator.

It has been hypothesised that intense metabolism of nectar-inhabiting yeasts (NIY) may change nectar chemistry, including volatile profile, which may affect pollinator foraging behaviours and consequently plant fitness. However, empirical evidence for the plant-microbe-pollinator interactions remains little known. To test this hypothesis, we use a bumblebee-pollinated vine Clematis akebioides endemic to southwest China as an experimental model plant. To quantify the incidence and density of Metschnikowia reukaufii, a cosmopolitan NIY in floral nectar, a combination of yeast cultivation and microscopic cell-counting method was used. To examine the effects of NIY on plant-pollinator interactions, we used real flowers filled with artificial nectar with or without yeast cells. Then the volatile metabolites produced in the yeast-inoculated nectar were analysed with coupled gas chromatography and mass spectrometry (GC-MS). On average 79.3% of the C.akebioides flowers harboured M.reukaufii, and cell density of NIY was high to 7.4×104 cells mm-3 . In the field population, the presence of NIY in flowers of C.akebioides increased bumblebee (Bombus friseanus) pollinator visitation rate and consequently seed set per flower. A variety of fatty acid derivatives produced by M.reukaufii may be responsible for the above beneficial interactions. The volatiles produced by the metabolism of M.reukaufii may serve as an honest signal to attract bumblebee pollinators and indirectly promote the female reproductive fitness of C.akebioides, forming a potentially tripartite plant-microbe-pollinator mutualism.

Pollinator limitation causes sexual reproductive failure in ex situ populations of self-compatible Iris ensata

ABSTRACTBackground: The absence of pollinators may prevent sexual reproduction and affect the distribution and persistence of individual plant populations, but the role of pollinators in shaping the patterns of distributions of plant species or populations has not been well studied.Aims: Here, we tested the hypothesis that failure of sexual reproduction due to the absence of pollinators may contribute to the disjunct distribution of Iris ensata.Methods: We assessed floral traits and pollinator visitation frequencies in three native and two ex situ populations. We also conducted controlled pollination experiments and examined progeny performance to estimate pollen limitation (PL) and inbreeding depression.Results: Hand-pollinations indicated that I. ensata was a partially self-compatible outcrosser. Sexual reproduction in our study region depended on Bombus trifasciatus. We observed inbreeding depression for seed set and germination, but not for seedling survival. Native populations had higher frequencies of pollinator visitation and lower pollen-limitation of seed set than ex situ populations. Among populations, the magnitude of PL was negatively related to pollinator visitation rate (P = 0.04).Conclusions: Pollinator limitation and inbreeding depression may both restrict the southern distribution of I. ensata, preventing its northward expansion, thus explaining the disjunct distribution of I. ensata in East Asia.

Ecological role of a flower-dwelling predator in a tri-trophic interaction in northwestern Patagonia

Flower-dwelling predators may play several ecological roles depending on their effects on the reproductive success of the plants that they use to forage. However, tri-trophic interactions often are context-dependent highlighting the importance of assessing both the overall top-down effect on plant fitness and predator behavioral and physiological attributes that shape that outcome. We studied the effect of the flower-dwelling crab spider Misumenops pallidus on the perennial herb Anemone multifida in a low-thicket in Northwestern Patagonia. We measured pollinator visitation frequency, florivory rate, plant fitness, spider abundance, and spider's physiological (e.g. camouflage) and behavioral attributes (e.g. host selection, fidelity) that aid to define its possible ecological role. Misumenops pallidus showed a generalist diet (mostly pollinators), camouflage strategies, and intraspecific selection for plants bearing higher number and longer trichomes. Additionally, it displayed host-fidelity with long periods of permanence in the selected host plant, occupying ∼25% of plant population. However, the presence of these spiders did not affect pollinator visitation rate, florivory or plant fitness, indicating a commensalism role. Our findings suggested that the asymmetric benefit in this plant-spider association may be attributed to a combination of factors. In particular, the low-to-moderate spider abundance, generalist diet and cryptic camouflage; all of which weaken the top-down effect on pollinators and plant fitness, especially whenever ecological redundant pollinators are present. However, temporal and/or spatial variation on spider population might enhance this asymmetric benefit for the spider, potentially changing its role from commensalism to antagonism.