Plant-pollinator Interactions Research Articles

Emergence of structure in plant–pollinator networks: low floral resource constrains network specialisation

Specialisation enhances the efficiency of plant–pollinator networks through the exchange of conspecific pollen transfer for floral resources. Floral resources form the currency of plant–pollinator interactions, but the understanding of how floral resources affect the structure of plant–pollinator networks remains modest. Previous theory predicts that optimally foraging animal species will specialise to improve resource acquisition under high resource availability. Although floral resource availability depends on both the plant production and animal consumption of the resources, previous work has assumed that production and availability are equivalent. This potentially may have led to erroneous inferences on the effect of resource availability on specialisation. We develop a mutualistic Lotka–Volterra consumer‐resource model to investigate the influence of floral resource availability on plant–pollinator network structure. The model incorporates animal adaptive foraging behaviour, floral resource dynamics, and density‐dependent dynamics. Specialisation, nestedness and modularity of simulated networks generated from the model under a wide range of parameters were explained using the generalised linear model. We found that the distinction between floral resource dynamics and plant density dynamics was necessary for partial specialisation of plant–pollinator networks. This is because floral resource dynamics constrained animal preference due to its depletion by animal species. Floral resource abundance had a positive effect on network specialisation, but animal density had a negative effect on network specialisation. Floral resource dynamics thus play key roles in the structure of plant–pollinator networks, distinctive from plant species density dynamics.

Landscape simplification leads to loss of plant–pollinator interaction diversity and flower visitation frequency despite buffering by abundant generalist pollinators

AbstractAimGlobal change, especially landscape simplification, is a main driver of species loss that can alter ecological interaction networks, with potentially severe consequences to ecosystem functions. Therefore, understanding how landscape simplification affects the rate of loss of plant–pollinator interaction diversity (i.e., number of unique interactions) compared to species diversity alone, and the role of persisting abundant pollinators, is key to assess the consequences of landscape simplification on network stability and pollination services.LocationFrance, Germany, and Switzerland.MethodsWe analysed 24 landscape‐scale plant–pollinator networks from standardised transect walks along landscape simplification gradients in three countries. We compared the rates of species and interaction diversity loss along the landscape simplification gradient and then stepwise excluded the top 1%–20% most abundant pollinators from the data set to evaluate their effect on interaction diversity, network robustness to secondary loss of species, and flower visitation frequencies in simplified landscapes.ResultsInteraction diversity was not more vulnerable than species diversity to landscape simplification, with pollinator and interaction diversity showing similar rates of erosion with landscape simplification. We found that 20% of both species and interactions are lost with an increase of arable crop cover from 30% to 80% in a landscape. The decrease in interaction diversity was partially buffered by persistent abundant generalist pollinators in simplified landscapes, which were nested subsets of pollinator communities in complex landscapes, while plants showed a high turnover in interactions across landscapes. The top 5% most abundant pollinator species also contributed to network robustness against secondary species loss but could not prevent flowers from a loss of visits in simplified landscapes.Main ConclusionsAlthough persistent abundant pollinators buffered the decrease in interaction diversity in simplified landscapes and stabilised network robustness, flower visitation frequency was reduced, emphasising potentially severe consequences of further ongoing land‐use change for pollination services.

Partitioning the contribution of bees with different traits and hoverflies to flower-visitor interaction networks

Insect pollinators are key to maintaining biodiversity and providing important ecosystem services. Among them, bee species (i.e., Apidae) and hoverflies (i.e., Syrphidae) are two of the most important and well-studied taxa worldwide. Yet, their relative contribution to the structural and dynamic properties of plant-pollinator interaction networks remains poorly understood. This is an important gap in knowledge given that these phylogenetically and functionally different groups might play different roles within their communities and respond in contrasting ways to anthropogenic perturbations.Here, we study the relative contribution of bee species (with different traits) and syrphids to maintain network properties (i.e., nestedness, network specialization (H2), and interaction diversity) and their influence on the temporal dynamics of these network metrics. To this end, we simulate species removals in community-wide flower-arthropod visitor interaction networks. These interactions were extensively sampled across four years in two different near-pristine temperate ecosystems in Japan.We found that bee species contribute significantly more than syrphids or any random combination of species to network nestedness, low specialization, and interaction diversity across months and years. In addition, bees also played a particularly important role in maintaining the observed temporal dynamics over time. Conversely, although syrphids were an abundant and species-rich group, they did not contribute so prominently to network metrics or temporal dynamics, with the exception of network complementary specialization, to which they contributed positively. In addition, smaller bee species and those that were active for longer periods were particularly important for interaction diversity and the number of interactions, respectively, and to maintain observed network temporal dynamics.Our results support that bee species, and especially the small ones, are cornerstone contributors to plant-visitor communities by shaping network properties and network temporal dynamics in natural ecosystems.

Floral attractants and rewards to pollinators in Mangifera indica L.

Floral attractants and rewards are essential in plant-pollinator interaction, pollen transfer to and from the flowers, and hence in crop production. In this trial, we determined the attractants and rewards of mango ‘Osteen’ cultivated under a plastic greenhouse. The attractants analyzed were inflorescence architecture and compactness, flower number, size and color patterns. Rewards determined were pollen quantity and its nutritious value and nectar volume and composition. The results show that mango forms panicles with more staminate than hermaphrodite flowers, but the latter are of higher size, more exposed to pollinator activity, and preferentially located in a better-nurtured position within the inflorescence. Pollen produced by staminate and hermaphrodite flowers was similar in quantity and quality. On the contrary, hermaphrodite flowers produced more nectar, likely because of the larger size of their nectary disks. Pollen and nectar present 17 and 22 metabolites, respectively, including carbohydrates, amino acids, and organic acids. Our study provides, for the first time, solid information about the floral attractiveness and rewards of mango cultivated under plastic greenhouses. This will help to understand the possible adaptations required for pollinating this crop under protected cultivation.

Glacier retreat triggers changes in biodiversity and plant–pollinator interaction diversity

AbstractDue to global warming, the worldwide retreat of glaciers is causing changes in species diversity, community composition, and species interactions. However, the impact of glacier retreat on interaction diversity and ecological networks remains poorly understood. An integrative understanding of network dynamics may inform conservation actions that support biodiversity and ecosystem functioning after glacier extinction. Here, we address how glacier retreat affects the frequency, diversity, and complexity of plant–pollinator interactions, both directly and indirectly through biodiversity change. We surveyed flower visitors (pollinators) and analyzed pollination networks across a gradient of 170 years of glacier retreat (Mont Miné glacier, Valais, Switzerland) which ranges from patchy grasslands to closed forests. We reported a strong impact of glacier retreat on both plant and pollinator communities. Notably, the diversity of plant–pollinator interactions was sharply affected by glacier retreat: interaction diversity increased few years after glacier retreat, but it ultimately decreased in late stages dominated by forests. In contrast, we found that plant–pollinator network complexity did not change with glacier retreat. Our results indicate that the development of plant–pollinator networks is a two-phases process. In the first phase, glacier retreat makes space to plant colonization. This initial increase in plant diversity drives the increase in pollinator and interaction diversity. The second phase is characterized by turnover as woody species encroaches and dominates the community, decreasing the diversity of plant species in ultimate instance. The local decrease of plant diversity leads to a local decrease in pollinator and interaction diversity. Slowing down woody encroachment and enhancing flower diversity, which is initially supported by the glacial landscape, may be key strategies for halting the erosion of ecological networks while increasing biodiversity and ecosystem functioning. Our research thus can help resolve the overarching question of how to conserve ecosystems once glaciers are extinct, pointing toward a composite role of both habitat structure and biological functions.

Pollinator-assisted plant phenotyping, selection, and breeding for crop resilience to abiotic stresses.

Food security is threatened by climate change, with heat and drought being the main stresses affecting crop physiology and ecosystem services, such as plant-pollinator interactions. We hypothesize that tracking and ranking pollinators' preferences for flowers under environmental pressure could be used as a marker of plant quality for agricultural breeding to increase crop stress tolerance. Despite increasing relevance of flowers as the most stress sensitive organs, phenotyping platforms aim at identifying traits of resilience by assessing the plant physiological status through remote sensing-assisted vegetative indexes, but find strong bottlenecks in quantifying flower traits and in accurate genotype-to-phenotype prediction. However, as the transport of photoassimilates from leaves (sources) to flowers (sinks) is reduced in low-resilient plants, flowers are better indicators than leaves of plant well-being. Indeed, the chemical composition and amount of pollen and nectar that flowers produce, which ultimately serve as food resources for pollinators, change in response to environmental cues. Therefore, pollinators' preferences could be used as a measure of functional source-to-sink relationships for breeding decisions. To achieve this challenging goal, we propose to develop a pollinator-assisted phenotyping and selection platform for automated quantification of Genotype × Environment × Pollinator interactions through an insect geo-positioning system. Pollinator-assisted selection can be validated by metabolic, transcriptomic, and ionomic traits, and mapping of candidate genes, linking floral and leaf traits, pollinator preferences, plant resilience, and crop productivity. This radical new approach can change the current paradigm of plant phenotyping and find new paths for crop redomestication and breeding assisted by ecological decisions.

Flower visits and pollinator pollen load networks reveal the effects of pollinator sharing on heterospecific pollen transfer in a subalpine plant community.

The mutualistic network of plant-pollinator also involves interspecific pollination caused by pollinator sharing. Plant-pollinator networks are commonly based on flower visit observations, which may not adequately represent the actual pollen transfer between co-flowering plant species. Here, we compared the network structure of plant-pollinator interactions based on flower visits (FV) and pollen loads (PL) on the bodies of pollinators and tested how the degree of pollinator sharing in the two networks affected heterospecific pollen transfer (HPT) between plant species in a subalpine meadow. The FV and PL networks were largely overlapped. PL network included more links than FV network. The positions of plant and pollinator species in the FV and PL networks were positively correlated, indicating that both networks could detect major plant-pollinator interactions. The degree of pollinator sharing, based on either the FV or the PL network, positively influenced the amount of heterospecific pollen transferred between plant species pairs. However, the degree of pollinator sharing had a low overall explanatory power for HPT, and the explanatory powers of the FV and PL networks were similar. Overall, our study highlights the importance of FV and PL for understanding the drivers and outcomes of plant-pollinator interactions, as well as their relevance to HPT.

Pollen load, pollen species diversity and conspecific pollen carried by pollinators across 24-hour cycles

Plant-pollinator interactions are key for the reproduction of wild plants and for food security. However, the role nocturnal pollinators play in wild plant communities is not yet clear. Specifically, it has rarely been studied whether nocturnal pollinators are comparable to diurnal ones in the pollination services they deliver in plant communities. We tested whether nocturnal pollinators have the potential to provide high pollination services to the plants they visit by carrying high conspecific pollen load. We studied pollen loads carried by nocturnal and diurnal pollinators captured over 24-hour cycles in co-flowering plant communities in Swiss ruderal meadows. Pollen load was less diverse at night, and the proportion of conspecific pollen carried by nocturnal pollinators was higher than that of diurnal ones. Because the majority of plant species visited at night were also visited during the day, floral resource availability could drive the observed patterns in pollen load and amount of conspecific pollen. Nevertheless, nocturnal pollinators do not only carry pollen but can remove and potentially deposit conspecific pollen to the plants they visit. Therefore, pollinators active at night might be an important pollination vector for more plant species than previously thought and should not be neglected in pollination studies.

The Hidden World of Insect-Plant Interactions: a review

This review examines the hidden world of plant-insect interactions by emphasizing on the sensory perception and behavior of phytophagous insects, nutritional influence on insect reproduction, host plant resistance, Insects, weed and crop interaction, Insect pollinator plant interaction, tri-trophic interaction, and insect biotechnology. It explores how insects use sensory cues to forage for food, find mates, perceive dangers, and navigate their environment. It also examines the influence of host plants on insect behavior and the use of chemical cues for communication. The potential use of semio-chemicals in pest management for sustainable agriculture is highlighted. Nutritional factors and their impact on insect reproductive success are also discussed, emphasizing the need for balanced diets. The different categories of host plant resistance and their effects on insects are examined. The interdependent relationships between insects, plants, and weeds in agricultural ecosystems are explored, with a focus on the role of insect pollinators. The decline of insect pollinators and the importance of studying them are emphasized. The importance of tri-trophic interactions in maintaining ecological balance and biodiversity is discussed. Moreover, the role of biotechnological techniques like genomics, proteomics, transcriptomics, and epigenetics in understanding insect plant interactions as well as developing insect pest control strategies is discussed.  The potential use of natural products produced by plants in environmentally friendly pest control methods is also examined. Overall, this review provides a comprehensive exploration of insect-plant interactions and the potential for sustainable pest control methods.

Drought stress influences foraging preference of a solitary bee on two wildflowers.

Pollinators provide critical ecosystem services, maintaining biodiversity and benefiting global food production. However, plants, pollinators, and their mutualistic interactions may be affected by drought, which has increased in severity and frequency under climate change. Using two annual, insect-pollinated wildflowers (Phacelia campanularia and Nemophila menziesii), we asked how drought impacts floral traits and foraging preferences of a solitary bee (Osmia lignaria) and explore potential implications for plant reproduction. In greenhouses, we experimentally subjected plants to drought to induce water stress, as verified by leaf water potential. To assess the impact of drought on floral traits, we measured flower size, floral display size, nectar volume, and nectar sugar concentration. To explore how drought-induced effects on floral traits affected bee foraging preferences, we performed choice trials. Individual female bees were placed into foraging arenas with two conspecific plants, one droughted and one non-droughted, and were allowed to forage freely. We determined that P. campanularia is more drought-tolerant than N. menziesii based on measures of turgor loss point, and confirmed that droughted plants were more drought-stressed than non-droughted plants. For droughted plants of both species, floral display size was reduced, and flowers were smaller and produced less, more-concentrated nectar. We found that bees preferred non-droughted flowers of N. menziesii. However, bee preference for non-droughted P. campanularia flowers depended on the time of day and was detected only in the afternoon. Our findings indicate that bees prefer visiting non-droughted flowers, likely reducing pollination success for drought-stressed plants. Lack of preference for non-droughted P. campanularia flowers in the morning may reflect the higher drought tolerance of this species. This work highlights the potentially intersecting, short-term physiological and pollinator behavioral responses to drought and suggests that such responses may reshape plant-pollinator interactions, ultimately reducing reproductive output for less drought-tolerant wildflowers.

Effects of climate change on Lepidoptera pollen loads and their pollination services in space and time.

Shifts in flowering time among plant communities as a result of climate change, including extreme weather events, are a growing concern. These plant phenological changes may affect the quantity and quality of food sources for specialized insect pollinators. Plant-pollinator interactions are threatened by habitat alterations and biodiversity loss, and changes in these interactions may lead to declines in flower visitors and pollination services. Most prior research has focused on short-term plant-pollinator interactions, which do not accurately capture changes in pollination services. Here, we characterized long-term plant-pollinator interactions and identified potential risks to specialized butterfly species due to habitat loss, fragmented landscapes, and changes in plant assemblages. We used 21years of historical data from museum specimens to track the potential effects of direct and indirect changes in precipitation, temperature, monsoons, and wildfires on plant-pollinator mutualism in the Great Basin and Sierra Nevada. We found decreased pollen richness associated with butterflies within sites, as well as an increase in pollen grain abundance of drought-tolerant plants, particularly in the past 10years. Moreover, increased global temperatures and the intensity and frequency of precipitation and wildfires were negatively correlated with pollen diversity. Our findings have important implications for understanding plant-pollinator interactions and the pollination services affected by global warming.

Sites dominated by common fiddleneck (Amsinckia menziesii var. intermedia) support diverse plant-pollinator interactions

Sites dominated by common fiddleneck (Amsinckia menziesii var. intermedia) support diverse plant-pollinator interactions

Effects of short- and long-term experimental warming on plant-pollinator interactions and floral rewards in the Low Arctic 
 

Plant phenological and growth responses to experimental warming are widely documented, but less is known about warming effects on plant-pollinator interactions. We investigated the effects of short- and long-term passive warming on flowering phenology, insect visitation, fruit production, and floral rewards in the Low Arctic in northern Alaska. To better understand the role of insect visitors in plant reproductive success, we quantified pollen loads on floral visitors and tested for pollen limitation in four species. Long-term warming advanced flowering onset in evergreen shrubs and forbs. Warming, in general, increased the duration of flowering for forbs, evergreen shrubs, and deciduous shrubs. Considering all growth forms together, long-term warming increased floral density. This pattern was primarily driven by deciduous and evergreen shrubs. Dipterans accounted for more visits than Hymenopterans, although Hymenopterans had higher pollen loads. Insect exclusion and warming decreased fruit set in the forb, <i>Bistorta officinalis</i>. Nectar volume in the deciduous shrub, <i>Vaccinium uliginosum</i>, was higher in the warmed plots than the control, but nectar quality did not differ. Advanced flowering onset, longer flowering duration, and increased flower density and nectar volume may have important implications for the pollinator community, warranting further research on long-term warming effects on tundra ecosystems.

Alpine Rhododendron population contractions lead to spatial distribution mismatch with their pollinators under climate change

The effect of global climate change on plant–pollinator interaction is not limited to changes in phenology and richness within communities but also includes the spatial mismatch caused by the inconsistency of geographical distribution changes. Subsequently, the pollinator interaction network may be remodeled or even disrupted. In this study, we simulated the suitable habitat niche of 15 Rhododendron species and their eight pollinator species as well as their overlapping versus geographical mismatch under the current and three future climate change scenarios in 2090s, using MaxEnt. Results showed that the suitable habitat of all Rhododendron species would decrease in 2090s. In particular, 10, 8, and 13 Rhododendron–pollinator assemblages would have a reduced spatial match region under the climate change scenarios, mainly due to the contraction of the suitable habitat of Rhododendron species. The results provide novel insights into the response of plant–pollinator interactions to global warming, useful to prioritize conservation actions of alpine plant ecosystems.

Floral traits and their connection with Pollinators and Climate.

Floral characteristics vary significantly among plant species, and multiple underlying factors govern this diversity. Although it is widely known that spatial variation in pollinator groups can exert selection on floral traits, the relative contribution of pollinators and climate to the variation of floral traits across large geographic areas remains a little-studied area. Besides furthering our conceptual understanding of these processes, gaining insight into the topic is also of conservation relevance: understanding how climate may drive floral traits variation can serve to protect plant-pollinator interactions under global change conditions. We used Rhododendron as a model system and collected floral traits (corolla length, nectar volume and concentrations), floral visitors, and climatic data on 21 Rhododendron species across two continents (North America-Appalachians and Asia-Himalaya). Based on this we quantified the influence of climate and pollinators to floral traits using phylogeny-informed analyses. Our results indicate that there is substantial variation in pollinators and morphological traits across Rhododendron species and continents. We came across four pollinator groups: birds, bees, butterflies, and flies. Asian species were commonly visited by birds, bees, and flies, while bees and butterflies were the most common visitors of North American species. The visitor identity explained nectar trait variation, with flowers visited by birds presenting higher volumes of dilute nectar and those visited by insects producing concentrated nectar. Nectar concentration and corolla length exhibited a strong phylogenetic signal across the analysed set of species. We also found that nectar trait variation in the Himalaya could also be explained by climate, which presented significant interactions with pollinator identity. Our results indicate that both pollinators and climate contribute and interact to drive nectar trait variation, suggesting that both can affect pollination interactions and floral (and plant) evolution individually and interacting with each other.

The effects of grazing on flowering and fruiting phenology in South Brazilian subtropical grasslands

In subtropical grasslands, characterized by the coexistence of species with different physiology, for example C3 and C4 grasses, studies on the reproductive patterns of plants at the community level are scarce. Most available studies are limited to plant-pollinator interactions, and do not include grasses, even though knowledge on phenology of this species group is highly relevant, e.g., for grazing management or ecological restoration. In this study, we monthly evaluated flowering and fruiting in Brazilian subtropical grasslands under different grazing intensities (high, moderate, low, very low, ungrazed) over one year. To estimate the effect of the seasonal variation on the phenology of functional groups (C3 grass, C4 grass, monocots, dicots, shrubs) we used circular statistics. The highest flowering activity occurred in October and November, while fruiting peaked in March and April. Shrubs had the highest number of flowers and fruits, and C4 grasses contributed the largest number of fruiting species. The flowering peak of most functional groups occurred in October, except for C4 grasses and shrubs that peaked in February and November, respectively. Fruiting of C3 grasses peaked in December, C4 grasses and shrubs were most abundant in April and dicots, and monocots peaked in October. Grazing treatments differed considerably in flowering and fruiting patterns for all species groups. Monocots and dicots herbs showed high flowering activity under intense grazing. C3 grasses presented highest peaks in moderate and low grazing intensities, while C4 grasses peaked in very low grazing, and shrubs showed the highest peaks in ungrazed plots. Flowering and fruiting occurred throughout the year in our study system, with clear variation among functional groups in response to climatic and management patterns. Our results can guide seed collection in the field or vegetation cutting for hay transfer, and thus should lead to improvements in the ecological restoration of subtropical grasslands.

Untangling biodiversity interactions: A meta network on pollination in Earth's most diverse tropical savanna.

Pollination is vital for ecosystem functioning, especially in biodiversity-rich regions like the Brazilian Cerrado. Our research establishes a comprehensive meta network of pollinator-plant interactions within this biome. We quantified the importance of different pollinator groups, identifying keystone species. We examined potential biases in sampling effort and the spatial behavior of interactions within the heterogeneous Cerrado plant physiognomies. Our investigation uncovered 1499 interactions among 293 plant species and 386 visitor species, with legitimate pollination accounting for 42.4% of the interactions. The network exhibited modularity, driven by bees and insects, with vertebrates bridging diurnal and nocturnal modules. While a generalized pattern emerged, high specialization existed within modules due to habitat diversity. Bees, particularly Apis mellifera (exotic) and Trigona spinipes (native), played central roles as network hubs. Hummingbirds and bats, engaged in specialized interactions showing strong connectivity within and between modules. Interestingly, invertebrate-vertebrate modules were more prevalent than expected in the meta network. However, a bias was evident, primarily within specific biogeographical districts with fragmented landscapes and intrusion from other biomes. Variations in plant species and endemism rates influenced pollinator occurrence and the Cerrado network topology. Our study offers valuable insights into pollinator-plant interactions within the Cerrado, encompassing both invertebrates and vertebrates. The modeled network represents a significant step in understanding the structural complexity of pollination networks, integrating partial networks from diverse pollination systems within heterogeneous habitats. Nevertheless, a biogeographical bias could limit a comprehensive understanding of network functionality across the Cerrado.

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.

Lack of pollinators selects for increased selfing, restricted gene flow and resource allocation in the rare Mediterranean sage Salvia brachyodon

Range contraction and habitat fragmentation can cause biodiversity loss by creating conditions that directly or indirectly affect the survival of plant populations. Fragmented habitats can alter pollinator guilds and impact their behavior, which may result in pollen/pollinator limitation and selection for increased selfing as a mechanism for reproductive assurance. We used Salvia brachyodon, a narrowly distributed and endangered sage from eastern Adriatic, to test the consequences of range contraction and habitat fragmentation. Molecular data indicate a severe and relatively recent species range reduction. While one population is reproductively almost completely isolated, moderate gene flow has been detected between the remaining two populations. The high pollen-to-ovule ratio and the results of controlled hand pollination indicate that S. brachyodon has a mixed mating system. Quantitative and qualitative differences in the community and behaviour of flower visitors resulted in limited pollination services in one population where no effective pollinator other than pollen and nectar robbers were observed. In this population, self-pollination predominated over cross-pollination. Various environmental factors, in which plant-pollinator interactions play a pivotal role, have likely created selection pressures that have led to genetic and phenotypic differentiation and different resource allocation strategies among populations.

Manipulation of soil mycorrhizal fungi influences floral traits.

Most plants form root hyphal relationships with mycorrhizal fungi, especially arbuscular mycorrhizal fungi (AMF). These associations are known to positively impact plant biomass and competitive ability. However, less is known about how mycorrhizas impact other ecological interactions, such as those mediated by pollinators. We performed a meta-regression of studies that manipulated AMF and measured traits related to pollination, including floral display size, rewards, visitation, and reproduction, extracting 63 studies with 423 effects. On average, the presence of mycorrhizas was associated with positive effects on floral traits. Specifically, we found impacts of AMF on floral display size, pollinator visitation and reproduction, and a positive but nonsignificant impact on rewards. Studies manipulating mycorrhizas with fungicide tended to report contrasting results, possibly because fungicide destroys both beneficial and pathogenic microbes. Our study highlights the potential for relationships with mycorrhizal fungi to play an important, yet underrecognized role in plant-pollinator interactions. With heightened awareness ofthe need for a more sustainable agricultural industry, mycorrhizal fungi may offer the opportunity to reduce reliance on inorganic fertilizers. At the same time, fungicides are nowubiquitous in agricultural systems. Our study demonstrates indirect ways in which plant-belowground fungal partnerships could manifest in plant-pollinator interactions.