Pollinator Visitation Rates Research Articles

Weighing the risks and benefits of flowering early in the spring for the woody perennial Prunus pumila.

There are advantages to flowering early in the spring, including greater pollinator fidelity and longer fruit maturation time. But plant phenology has advanced in recent years, making many plants vulnerable to freezing damage from late frosts. To determine the costs and benefits of flowering early in the growing season, we exposed Prunus pumila plants to two freezing treatments and a delayed flowering treatment in subsequent years. Data were collected on ovary swelling, fruit production, and pollinator visitation on hand- and open-pollinated plants in all treatments. We also measured tissue damage after freeze events. Our results suggest that flowering time and temperature affect reproductive success, with fewer fruits produced after hard freezes. The same was not true for light freezes, which had minimal impact on reproduction. Freezing damage to plants after a hard freeze did affect the number of dipteran pollinators but not the overall pollinator visitation rate. Despite the clear impact of freezing temperatures on plant reproduction, flowering early provided an advantage in that reproductive output decreased with delayed flowering. Our findings suggest that Prunus pumila will retain the ability to attract pollinators and produce viable seeds if exposed to false spring conditions that involve a light freeze, but hard freezes may reduce yield by an order of magnitude. Although the advantages to flowering early may outweigh the risk of freezing damage under current conditions, it is possible that flower viability may be constrained under continued climate warming.

Vegetative traits, floral biology, and mutualistic interactions in the tropical mountain shrub Ribes ciliatum (Grossulariaceae)

Plant species in tropical mountain ecosystems experience significant environmental variation across short spatial distances. These systems offer an opportunity to assess geographic variation in plant traits in relation to biotic and abiotic environments. We examined plant vegetative and reproductive traits in the shrub R. ciliatum across two native conifer forests in central Mexico. We measured plant height, number of branches, leaf size, flower production, floral morphology, floral longevity, and plant reproductive success in R. ciliatum populations found in fir forests (3100 m) and Hartweg's pine forests (subalpine habitat, 3700 m). We also quantified the level of pollinator dependence, pollinator visitation rates, and fruit consumption rates by frugivorous birds in both populations. Plants were shorter and had smaller leaves in the subalpine forest than in the fir forest. Floral longevity decreased in the subalpine forest, but flower production, flower size, and fruit weight remained similar across populations. Fruit set and pollinator visitation rates were higher in the subalpine forest; however, seed weight and fruit consumption rates did not differ between sites. Hummingbirds and bumblebees were the primary pollinators of R. ciliatum, and the bird Ptiliogonys cinereus was the most important fruit consumer at both sites. Fruit set was entirely dependent on pollinators. Reduced plant size in the subalpine forest coincides with a general pattern associated with high mountain environments. In contrast, reproductive characters had a closer relationship to the pollination environment. The absence of variation in flower size and shape was consistent with the similarity in the composition of the pollinator community. Meanwhile, compared to lower-elevation forests, the subalpine forest exhibited shorter-lived flowers and increased fruit set, associated with higher pollinator visitation rates. Ribes ciliatum is a key resource for pollinators and frugivores at a time of year when few other floral resources are available in these high-elevation mountain forests.

Woody flowering plants support early-spring pollinators in urban greenspaces

One threat pollinators face in a rapidly changing climate is the decoupling of their activity period from the blooming period of their host plants. Pollinators active in the earliest part of spring may be especially susceptible, as there are few alternative food resources available if they become active before their host plants begin blooming. Thus, urban landscapes, although often associated with decreased insect biodiversity, may buffer pollinators from such food shortages by offering a diversity of both native and exotic plant species that bloom in the late winter and early spring. However, more data are needed to ascertain the degree to which pollinators utilize flowers of spring-blooming exotic species. Here, we surveyed flower-visiting Hymenoptera and Diptera on 26 flowering plant taxa in three urban botanical gardens in the Oklahoma City metropolitan area in the early spring (March and April). We found that flowers of both native and exotic plants were attractive to Hymenoptera and Diptera, although pollinator visitation rates varied by more than an order of magnitude across plant taxa. Overall, woody plants were more attractive to pollinators compared to herbaceous plants, regardless of whether the plant was native or exotic. Implications for insect conservation: Our results suggest that regardless of native status, urban plants that bloom in the early spring—especially woody species—may be coopted to support pollinators that are especially susceptible to climate change. However, care needs to be taken to select plant species and varieties that pollinators will actually use.

Plant Virus Impacts on Yield and Plant-Pollinator Interactions Are Phylogenetically Modulated Independently of Domestication in Cucurbita spp.

Plant defenses are conserved among closely related species, but domestication can alter host genotypes through artificial selection with potential losses in host defenses. Therefore, both domestication and host phylogenetic structure may influence plant virus infection outcomes. Here, we examined the association of phylogeny and domestication with the fitness of infected plants. We inoculated three pairs of domesticated and wild/noncultivated squash (Cucurbita spp.) with a combination of two viruses commonly found to coinfect cucurbits, zucchini yellow mosaic virus and squash mosaic virus, and recorded fitness traits related to flowers, pollination, fruit, and seed viability in the field over 2 separate years. In an additional field experiment, we recorded the relative abundance of both viruses via RT-qPCR. We found a gradient of susceptibility across the six tested lineages, and phylogenetic structure, but not domestication, contributed to differences in infection outcomes and impacts on several fitness traits, including fruit number, fruit weight, and germination. Plant virus infection also impacted the quantity and quality of floral rewards and visitation rates of specialist bee pollinators. There were no detectable differences in viral load between the six host taxa for either virus individually or the ratio of zucchini yellow mosaic virus to squash mosaic virus. Our results highlight the importance of phylogenetic structure in predicting host susceptibility to disease across wild and domesticated plants and the ability of several hosts to maintain fitness in the field despite infection. Broader consequences of plant pathogens for beneficial insects, such as pollinators, should also be considered in future research.

Differential impacts of land‐use change on multiple components of common milkweed (Asclepias syriaca) pollination success

AbstractLand‐use change is one the greatest threats to biodiversity and is projected to increase in magnitude in the coming years, stressing the importance of better understanding how land‐use change may affect vital ecosystem services, such as pollination. Past studies on the impact of land‐use change have largely focused on only one aspect of the pollination process (e.g., pollinator composition, pollinator visitation, and pollen transfer), potentially misrepresenting the full complexity of land‐use effects on pollination services. Evaluating the impacts across multiple components of the pollination process can also help pinpoint the underlying mechanisms driving land‐use change effects. This study evaluates how land‐use change affects multiple aspects of the pollination process in common milkweed populations, including pollinator community composition, pollinator visitation rate, pollen removal, and pollen deposition. Overall, land‐use change altered floral visitor composition, with small bees having a larger presence in developed areas. Insect visitation rate and pollen removal were also higher in more developed areas, perhaps suggesting a positive impact of land‐use change. However, pollen deposition did not differ between developed and undeveloped sites. Our findings highlight the complexity evaluating land‐use change effects on pollination, as these likely depend on the specific aspect of pollination evaluated and on the of the intensity of disturbance. Our study stresses the importance of evaluating multiple components of the pollination process in order to fully understand overall effects and mechanisms underlying land‐use change effects on this vital ecosystem service.

Meta-analyses of reproductive changes in angiosperm populations in response to elevation reveal a lack of global patterns.

Elevation is a major factor shaping plant populations on a global scale. At the same time, reproductive traits play a major role in plant fitness. With increasing altitude and increasingly harsh conditions, decreases in pollinator visitation rates, sexual investment, seed set, and heterozygosity (due to increased selfing) are expected. In response, selection and/or phenotypic plasticity could lead to an increase in plants' floral displays to increase their attractiveness to pollinators and compensates for the negative fitness impacts of reduced pollinator activity. A large body of literature tests these hypotheses at the among-species level, but empirical evidence at the population level (i.e., wihin-species), where adaptive change may occur, is still limited to species-specific studies. Unravelling the global patterns of change in the reproductive traits, flower visitation rates and heterozygosity of plant populations across variable environmental conditions, especially climate can help us to understand how species are able to cope with shifting conditions associated with global change, particularly in mountains. Here, we used meta-analytic approaches to assess the reproductive changes of plant populations in response to elevation on a global scale. We used a data set with 243 paired populations of plants at 'lower' and 'higher' elevations, spanning an elevation range of 0-4380 m asl and taken from 121 angiosperm species and 115 published studies. We analyzed changes in flower number, size and longevity, pollen production, flower visitation rate, seed set and expected heterozygosity.We then tested whether the observed patterns for each trait were dependent upon plant phylogeny and various ecogeographical factors and species traits. We found no evidence of elevation having a global effect on the reproductive traits of angiosperm populations. This null global pattern was not affected by geograph or phylogenetics. Our results suggest that changes in reproductive traits, flower visitation rates, and heterozygosity in plant populations across elevations are specific to each species and ecosystem. Hence, macroevolutionary (across species) and macroecological patterns of elevation of plant reproduction reported previously are apparently not simply the outcome of microevolutionary changes (within species). This apparent specificity of response across plant species poses difficulties in predicting the effects of global changes and, specifically, climatic changes, on the fate of plant species, populations, and communities.

Influence of flowering red clover on flower visitation in a sweet corn agroecosystem

Agricultural intensification and the conversion of natural landscapes into annual cropping systems have contributed to declines in pollinator abundance and biodiversity. Increasing the abundance of flowering plants within crop fields is an often-overlooked practice that may be used to help sustain and enhance pollinator populations. In this study, the influence of red clover (Trifolium pratense) used as an interplanted living mulch on pollinator richness and visitation rates was evaluated and compared with monoculture sweet corn habitats. Treatments included sweet corn interplanted with red clover or monoculture with or without cover crop residue. Weekly visual observations of foraging floral visitors revealed that multiple species of bumblebees and butterflies, as well as honeybees frequently visited red clover flowers. Observations of visitors foraging on sweet corn tassels during pollen shed revealed distinct insect communities were attracted by sweet corn and red clover plants. Findings provided evidence that the inclusion of red clover in crop fields can increase the diversity and abundance of bees and butterflies on arable lands by serving as an important food source.

Effect of robbing intensity on reproductive success of Symphytum officinale (Boraginaceae).

The intervention of nectar robbers in plant pollination systems will cause some pollinators to modify their foraging behavior to act as secondary robbers, consequently adopting a mixed foraging strategy. The influence of nectar robbing on pollinator behavior may be affected by spatio-temporal difference of robbing intensity, and consequently, may have different effects on the pollination of host plants. However, whether and how the nectar robbing might influence pollinators under different robbing intensity still needs further investigation. In this study, Symphytum officinale was used to detect the effect of nectar robbers on pollinators under different robbing intensity as well as their effects on plant reproductive success. Six robbing levels and three bumblebees with mixed foraging behaviors were used to evaluate the effect of different robbing intensity on pollinator behavior, visitation rate, flower longevity and pollen deposition. Our results indicated that the robbing rate increased gradually with the proportion of robbed flowers, but which did not affect the frequency of legitimate visits. The increase of robbing rate promoted the corolla abscission, and then enhanced the self-pollen deposition, but which had no significant effect on cross-pollen deposition. These results indicate that the overall fitness of S. officinale was improved by combined self and cross-pollination modes when visited by both pollinators and nectar robbers simultaneously. Although nectar robbing is not uncommon, its consequences for pollination in the interaction web have not been well studied. Our results emphasize the significance of indirect impacts in mediating the adaptive outcomes of species interactions.

Fire effects on pollination and plant reproduction: a quantitative review.

Fire may favour plant flowering by opening the vegetation and increasing abiotic resource availability. Increased floral display size can attract more pollinators and increase the absolute fruit and seed production immediately after the fire. However, anthropogenic increases in fire frequency may alter these responses. We aim to assess the effects of fire on pollination and reproductive success of plants at the global scale. We performed a systematic literature review and meta-analyses to examine overall fire effects as well as different fire parameters on pollination and on plant reproduction. We also explored to what extent the responses vary among pollinators, pollination vectors, plant regeneration strategies, compatibility systems, vegetation types and biomes. Most studies were conducted in fire-prone ecosystems. Overall, single fires increased pollination and plant reproduction but this effect was overridden by recurrent fires. Floral visitation rates of pollinators were enhanced immediately following a wildfire, and especially in bee-pollinated plants. Fire increased the absolute production of fruits or seeds but not the fruit or seed set. The reproductive benefits were mostly observed in wind-pollinated (graminoids), herbaceous and resprouter species. Finally, fire effects on pollination were positively correlated with fire effects on plant reproductive success. Fire has a central role in pollination and plant sexual reproduction in fire-prone ecosystems. The increase in the absolute production of fruits and seeds suggests that fire benefits on plant reproduction are likely driven by increased abiotic resources and the consequent floral display size. However, reproduction efficiency, as measured by fruit or seed set, does not increase with fire. In contrast, when assessed on the same plant simultaneously, fire effects on pollination are translated into reproduction. Increased fire frequency due to anthropogenic changes can alter the nature of the response to fire.

Intensive pasture management alters the composition and structure of plant-pollinator interactions in Sibiu, Romania.

Land management change towards intensive grazing has been shown to alter plant and pollinator communities and the structure of plant-pollinator interactions in different ways across the world. Land-use intensification in Eastern Europe is shifting highly diverse, traditionally managed hay meadows towards intensive pastures, but few studies have examined how this influences plant-pollinator networks. We hypothesized that the effects of intensive grazing on networks will depend on how plant communities and their floral traits change. We investigated plant and pollinator diversity and composition and the structure of plant-pollinator interactions near Sibiu, Romania at sites that were traditionally managed as hay meadows or intensive pastures. We quantified the identity and abundance of flowering plants, and used transect walks to observe pollinator genera interacting with flowering plant species. We evaluated the effects of management on diversity, composition and several indices of network structure. Pollinator but not plant diversity declined in pastures and both plant and pollinator taxonomic composition shifted. Functional diversity and composition remained unchanged, with rather specialized flowers having been found to dominate in both hay meadows and pastures. Apis mellifera was found to be the most abundant pollinator. Its foraging preferences played a crucial role in shaping plant-pollinator network structure. Apis mellifera thus preferred the highly abundant Dorycnium herbaceum in hay meadows, leading to hay meadows networks with lower Shannon diversity and interaction evenness. In pastures, however, it preferred less abundant and more generalized flower resources. With pollinators being overall less abundant and more generalized in pastures, we found that niche overlap between plants was higher. With both hay meadows and pastures being dominated by plant species with similar floral traits, shifts in pollinator preferences seem to have driven the observed changes in plant-pollinator interaction networks. We thus conclude that the effects of grazing on pollinators and their interactions are likely to depend on the traits of plant species present in different management types as well as on the effects of grazing on plant community composition. We thereby highlight the need for better understanding how floral abundance shapes pollinator visitation rates and how floral traits may influence this relationship.

Negative Effects of Pollen Drought Stress on Floral Volatiles, Floral Nectar, Pollinator Behavior, and Seed Production in Ocimum basilicum Plants

Ocimum basilicum is an aromatic plant belonging to the family of Lamiaceae. Many biotic and abiotic factors particularly drought stress influences its reproduction. Drought stress can harm the pollen grains of O. basilicum plants and disrupt the production of floral volatiles, reduce floral rewards for pollinators, decrease pollinator activity, and ultimately result in a decline in the seed set. These detrimental impacts highlight the importance of sufficient pollen availability for the successful reproduction and survival of plant species. The reproduction in plants is significantly impacted by drought stress, as it can directly or indirectly alter the attraction of pollinators. In this study, the effect of drought stress in O. basilicum plants was investigated by comparing drought- with no drought-stressed plants in order to examine various elements including: (1) nectar quantity and quality (2) pollen production (3) flower volatile emissions (4) pollinator visitation rates from both domesticated and wild species, and (5) the plant’s' reproductive outcomes, which contributes to the knowledge of the relationship between drought stress and pollination on O. basilicum. The planting was done in two different locations within the Saran division of Bihar state in India, first one is Chapra town and second one is Siwan town, in June 2019. The result indicated that plants with drought conditions, in contrast to drought free plants, produced a reduced quantity of pollen and had a decrease of the number of flowers and the volume of nectar produced per flower. Furthermore, drought affected plants produced nectar with a lower percentage of sucrose in relation to the total sugar content. Bees visiting rate was low compared to control plants and plants emitted more Z-3-hexenol, C4H8O, C5H10O, and Isovaleraldehyde. Moreover, this study utilized HPLC analysis to investigate the impact of drought stress on the floral nectar of O. basilicum plants. The findings revealed significant changes in nectar composition, highlighting the susceptibility of plantpollinator interactions and seed production to environmental stress factors.

Effects of agricultural landscape heterogeneity on pollinator visitation rates in Mediterranean oilseed rape

Agricultural intensification, by changing land use and modifying the yearly configuration and composition through crop sequences, affects the abundance and diversity of pollinators and, consequently, pollination. This study aims to assess the impact of the characteristics of agricultural landscapes on pollinator abundance in the Mediterranean region. We studied the response of three major wild pollinator groups (hoverflies, bumblebees, and wild bees) to four landscape characteristics: three related to composition, namely, equivalent crop diversity in the sampling year (eRg), previous year equivalent crop diversity (eRgP) and percentage of seminatural habitats (SNH), and one related to landscape configuration, namely, mean field size (MFS). For this evaluation, we selected twenty-two oilseed rape fields (OSRs) differing in surrounding landscape characteristics within a 1-km radius. Multimodel inference indicates that landscape variables affect pollinator groups differently. The percentage of SNH was the most important variable having a positive influence on the abundance of bumblebees, while eRgP and MFS were found to be important for the abundance of wild bees and hoverflies. These data allow us to prioritize actions aimed at specific groups of pollinators, improve agricultural landscape schemes, promote the conservation of wild pollinators, promote crop diversity at the landscape scale and increase the extent of seminatural areas.

Variation in flower size and shape of Impatiens capensis is correlated with urbanization in Montreal, Canada.

Urbanization is changing the conditions in which many species live, forcing them to adjust to these novel environments. Floral size and shape are critical traits for the reproduction of plants pollinated by animals as they are involved in the attraction of pollinators and in efficient pollination. Variation in size and shape could be affected by urbanization via its modification of the abiotic environment (habitat fragmentation, water availability, temperature, soil properties), or via its impact on the biotic environment of plants (pollination, herbivory). Although numerous studies have assessed the impact of urbanization on pollinator communities and many plant traits, few have investigated its impact on floral size and shape while quantifying the proportion of the total urbanization effect that is due to biotic interactions. In this study, we tested if urbanization and pollinator visitation rates affect the flower shape of the spotted jewelweed, Impatiens capensis. We quantified the size and shape of flowers in frontal and profile views using geometric morphometrics for 228 individuals from six populations from the region of Montreal, Canada. Pollinator visitation rates were estimated at each site and the main pollinators were found to be bumblebees, honeybees and hummingbirds. We found that floral size and shape are significantly correlated with urbanization as measured by the amount of vegetation in the surrounding environment of the plants (mean normalized vegetation index, NDVI) and by the visitation rates of bumblebees and honey bees. Partitioning of the total flower shape variation suggests that urbanization affects flower shape through abiotic factors and via its impact on pollinator visitation rates. While further studies from other cities are necessary to confirm the role of urbanization in shaping the floral shape of I. capensis, these results support the idea that urbanization could affect flower shapes.

Complex floral traits shape pollinator attraction to flowering plants in urban greenspaces

Urban greenspaces are recognized as a benefit to pollinator conservation. Selective planting of attractive flowering plants can improve the conservation value of urban greenspaces. However, the functional traits of flowering plants that moderate pollinator preference merits further study. We analyzed 98 ornamental plants and spontaneous plant species for ten categories of floral and plant traits across twelve parks or campus greenspaces in Wuhan, a megacity located in central China. Our results revealed that: (1) Plant species vary enormously in their pollinator visitation rate. (2) For Lepidoptera, the number of individuals to the plot was lower for disk/bowl-shaped flowers than other flower shapes, and it was negatively corelated with corolla tube length. The number of Diptera individuals to the plot was higher for white, red/pink and yellow/orange flowers than blue/violet flowers. (3) Honeybees preferred exotic annual/biennial herbaceous species, with disk/bowl and flag flowers. Solitary bees preferred horizontal, lip or flag flowers. Diptera most frequently visited upward-facing, yellow/orange flower heads and Lepidoptera preferred horizontal, funnel-shaped flowers or flower heads. Blue/violet flowers and a diverse floral orientation were preferred by most pollinator groups. We recommend planting native woody plants (Nandina domestica, Thymus quinquecostatus, Lagerstroemia indica, and Tamarix austromongolica) and attractive exotic plants (Centaurea cyanus, Borago officinalis, Portulaca grandiflora, and Echinacea purpurea) to support multiple pollinator groups. As preferences differ among pollinators, increasing the species richness of flowering plants is conducive to promote overall pollinator diversity.

The effects of pesticides on tomato pollinators depend on application practices and floral visitor assemblage

AbstractPesticide use affects biodiversity and ecosystem service provision. Yet, such effects may vary between pesticides, dosage, application timing and pollinator assemblage in the study area. Understanding such diversity of effects is essential to enable integrated pest management practices that minimize negative impacts on pollinators. Here, we use a controlled experiment to compare different strategies of pesticide application in tomato crops: no application, low‐intensity applications (every 7 days) and high‐intensity application (every 3–4 days) with the last being the usual practice used by farmers in the study region. We focus on imidacloprid that is a neonicotinoid insecticide commonly used in Brazil. We show the negative effects of imidacloprid on the pollinator visitation rate of tomato flowers varied between flower visitor species. While the bee Paratrigona lineata was negatively affected by the imidacloprid application, no effects were detected when analysing all other bees as a group, indicating a null net effect. Although some studies have shown this insecticide is extremely harmful to bees' health, others showed that some bees do not avoid it, which may explain our results. However, the visitation rate recovery for P. lineata was only detected in the less than the more intensive treatment after imidacloprid applications ceased. The fact that no differences in fruit production were detected between treatments (including control blocks) could result from a null net effect of the negative effects on pollinators and positive effects on pest control. Further studies would be needed to disentangle the two effects.

Effects of meliponiculture Tetragonula laeviceps on pollinator diversity and visitation rate and citrus productivity in West Java, Indonesia

Abstract. Nurdiansyah MA, Abduh MY, Permana AD. 2023. Effects of meliponiculture Tetragonula laeviceps on pollinator diversity and visitation rate and citrus productivity in West Java, Indonesia. Biodiversitas 24: 5757-5763. Citrus reticulata var. Rimau Gerga Lebong (RGL) is a prominent Indonesian citrus variety, yet its global productivity is facing challenges due to decreasing diversity in pollinators. This study aimed to bolster the productivity of C. reticulata var. RGL in Bandung by introducing Tetragonula laeviceps Smith 1857 (Hymenoptera: Apidae). Simultaneously, the study explored the influence of pollinator diversity, foraging behavior, and visitation rates and compared the results with open and wind pollination. Field investigations were conducted to observe the pollination activities of T. laeviceps and eight wild pollinator species, including Apis cerana Fabricius 1793, Ceratina cognata Smith 1879, Xylocopa confusa Pérez 1901, Xylocopa latipes Drury 1773, Vespa affinis Linnaeus 1764, Dolichoderus thoracicus Smith 1860, Papilio demoleus Linnaeus 1758, and Catopsilia pyrantel Linnaeus 1758. T. laeviceps exhibited the highest relative abundance (34.87%) and an average time spent of 72.11 seconds per flower. Visitation rates were highest during noon (10:00 to 13:00) at 0.31 pollinators/hour/flower, influenced by temperature, relative humidity, and light intensity. The phenological stages of C. reticulata var. RGL spanned 240 days. Fruit set, fruit weight, and estimated citrus productivity were significantly higher in T. laeviceps and open pollination compared to wind pollination. This study highlights the suitability of T. laeviceps as an effective pollinator for C. reticulata var. RGL. The findings have implications for the conservation and management of pollinator populations to ensure sustainable citrus production in the declining global diversity.

Pollinator asynchrony drives the temporal stability of flower visitation rates, but not of plant reproductive success

Abstract The stability of ecological communities over time, often quantified using their aggregated abundance or biomass, is thought to be influenced by species richness and the asynchrony of species abundance fluctuations. However, the relationship between community stability and the stability of ecosystem functioning provided by this community has been little explored, especially for functions involving several trophic levels such as plant pollination. Understanding the mechanisms driving community stability and how this should be related to the stability of ecosystem functions is important to predict the resilience of communities in front of the increasing threats to biodiversity. Using a 5‐year dataset across 13 Mediterranean shrublands and 12 plant species, we assessed the effect of pollinator richness and asynchrony as drivers of stability in plant visitation rates and plant reproductive success. Additionally, we analysed whether the effects of species richness and visitation rate on plant reproductive success were consistent over the years. The stability of plant visitation rates is driven by the asynchrony of pollinator species abundances, but the effect of pollinator species richness is only indirect, as richer communities also tend to have more asynchronous populations. In contrast, the stability of plant reproductive success is not related to the stability of pollinator visitation rates. A year‐by‐year analysis reveals that plants in the studied system are unlikely to be limited by pollinator abundance except in specific years, blurring any potential effect of visitation rate stability on reproductive success stability. Synthesis: We highlight the importance of asynchronous fluctuating species that are redundant in their function as an important factor for the stability of ecosystems. This is particularly important for pollinators with diverse responses to environmental fluctuations, as their asynchrony between years ensures stable levels of flower visitation rates. However, we warn that final ecosystem functions such as plant reproductive success, which depends not only on pollinators but on plant competition or resource availability, might be decoupled from first order ecosystem functions (i.e. visitation rates and pollen deposition) when pollination is not a limiting factor.

Pollination supply models from a local to global scale

Abstract. Ecological intensification has been embraced with great interest by the academic sector but is still rarely taken up by farmers because monitoring the state of different ecological functions is not straightforward. Modelling tools can represent a more accessible alternative of measuring ecological functions, which could help promote their use amongst farmers and other decision-makers. In the case of crop pollination, modelling has traditionally followed either a mechanistic or a data-driven approach. Mechanistic models simulate the habitat preferences and foraging behaviour of pollinators, while data-driven models associate georeferenced variables with real observations. Here, we test these two approaches to predict pollination supply and validate these predictions using data from a newly released global dataset on pollinator visitation rates to different crops. We use one of the most extensively used models for the mechanistic approach, while for the data-driven approach, we select from among a comprehensive set of state-of-the-art machine-learning models. Moreover, we explore a mixed approach, where data-derived inputs, rather than expert assessment, inform the mechanistic model. We find that, at a global scale, machine-learning models work best, offering a rank correlation coefficient between predictions and observations of pollinator visitation rates of 0.56. In turn, the mechanistic model works moderately well at a global scale for wild bees other than bumblebees. Biomes characterized by temperate or Mediterranean forests show a better agreement between mechanistic model predictions and observations, probably due to more comprehensive ecological knowledge and therefore better parameterization of input variables for these biomes. This study highlights the challenges of transferring input variables across multiple biomes, as expected given the different composition of species in different biomes. Our results provide clear guidance on which pollination supply models perform best at different spatial scales – the first step towards bridging the stakeholder–academia gap in modelling ecosystem service delivery under ecological intensification.

Compatibility systems and pollinator dependency in morning glory species (Convolvulaceae)

BackgroundThe Convolvulaceae is a large family containing species exhibiting a range of breeding systems and pollinated by diverse animal taxa. We studied the pollination ecology of 15 Convolvulaceae species, representing seven genera (Argyreia Lour., Camonea Raf., Evolvulus L., Hewittia Wight & Arn., Ipomoea L., Merremia Dennst. ex Endl., and Operculina Silva Manso), in northeastern Thailand, a family that is highly diverse yet understudied in the paleotropics. Specifically, we studied their compatibility systems and degrees of pollinator dependency using pollination experiments, examined pollinator composition and visitation rates using video observation, and determined if there is an association between pollinator visitation rates and degree of pollinator dependence.ResultsOur results showed that most species are self-compatible, but the degree of pollinator dependence varies. Six species were found to be highly dependent on pollinators, as two are self-incompatible and four are self-compatible but had reduced seed set when pollinators were excluded, possibly due to herkogamy. Seven species showed low dependence on pollinators and seed set remained high when pollinators were excluded. Pollinator dependence was inconclusive for two species as seed set was low in all pollination treatments. We also found an association between pollinator visitation rates and degree of pollinator dependence. Specifically, species exhibiting high pollinator dependence received frequent visits from pollinators, while species exhibiting low pollinator dependence either received frequent visits from pollinators (and received high amounts of xenogamous pollen) or infrequent visits from pollinators (and received significantly lower amounts of xenogamous pollen). Most of our study species were primarily visited by bees (e.g., Lasioglossum, Amegilla, Apis, and meliponines), with the exception of one night-blooming species that was visited primarily by crepuscular butterflies and hawkmoths.ConclusionsThe cumulative findings of this study demonstrate how pollinator dependence is influenced by breeding system, and suggest that pollinator visitation is consistently high for species exhibiting high pollinator dependence but varies across species exhibiting low pollinator dependence. Our findings are also important for assessing the conservation risks of paleotropical Convolvulaceae.

Nitrogen addition affects floral and vegetative traits, reproduction, and pollinator performance in Capsicum annuum L.

It has been demonstrated that nitrogen (N) addition alters flower morphology, floral rewards and pollinator performance. However, little is known about the effects of N addition on plant reproduction, including fruit set and seed set during selfing and outcrossing, floral and vegetative traits, and pollinator performance. We hypothesized that N addition would influence fruit set, seed set in selfed and outcrossed flowers, the relationship between vegetative and flower traits, and pollinator performance. A 2-year pot experiment was conducted in which Capsicum annuum was exposed to three levels of relatively short-term N supply, i.e. 0 g m-2 (no N addition, as a control), 4 g m-2 (4N) and 16 g m-2 (16N), which are equivalent to about 0-, 1- and 4-fold of the peak local N deposition. We measured flower rewards, flower morphology, flowering phenology, as well as pollinator visitation rate, fruit set and seed set by self- and outcross-fertilization of C. annuum. The four levels of N addition increased plant biomass, biomass allocation to flowers, flower size, stigma-anther separation, nectar production and pollen production, resulting in an increase in pollinator visitation and fruit set. Nevertheless, the control and 16 levels of N addition reduced plant biomass, biomass allocation to flowers, flower size and stigma-anther separation, and nectar and pollen production, and consequently decreased pollinator visitation and fruit set. Exclusion of pollinators and hand-pollination experiments revealed that low levels of N addition were associated with high seed set in outcrossed flowers; however, this trend was reversed in flowers grown in the control and 16N treatments. Our results suggest that an optimal level of 4N can enhance the correlation between flower traits, pollinator performance and plant reproduction. Our findings cast new light on the underlying mechanisms of plant-pollinator interactions and plant adaptation to nitrogen deposition.