Pollinator Traits Research Articles

Evolutionary emergence of plant and pollinator polymorphisms in consumer-resource mutualisms

Mutualism is considered a major driver of biodiversity, as it enables extensive codiversification in terrestrial communities. An important case is flowering plants and their pollinators, where convergent selection on plant and pollinator traits is combined with divergent selection to minimize niche overlap within each group. In this article, we study the emergence of polymorphisms in communities structured trophically: plants are the primary producers of resources required by the primary consumers, the servicing pollinators. We model natural selection on traits affecting mutualism between plants and pollinators and competition within these two trophic levels. We show that phenotypic diversification is favored by broad plant niches, suggesting that bottom-up trophic control leads to codiversification. Mutualistic generalism, i.e., tolerance to differences in plant and pollinator traits, promotes a cascade of evolutionary branching favored by bottom-up plant competition dependent on similarity and top-down mutualistic services that broaden plant niches. Our results predict a strong positive correlation between the diversity of plant and pollinator phenotypes, which previous work has partially attributed to the trophic dependence of pollinators on plants.

The specialised buzz pollination syndrome poses a partial barrier to plant invasions

Abstract Plants that exhibit generalised pollination syndromes have been hypothesised to become invasive more easily compared with specialists, yet the degree to which specialised pollination traits inhibit plant invasions is unknown. One such specialisation is the buzz pollination syndrome, which encompasses specialised floral traits that restrict pollen access (typically poricidal anthers) and benefits from specialised insect behaviour for pollen extraction. We reviewed the literature on buzz pollination of invasive plants to assess whether: (1) plant species exhibiting specialised pollination syndromes are underrepresented as invasive species, and (2) species with specialised pollination syndromes that have become invasive can reproduce in the absence of specialist buzzing pollinators. Synthesis. We found 2.5% (117/4630) of invasive angiosperms have poricidal anthers, which is an underrepresentation of the proportion of global angiosperms that are estimated to have poricidal anthers (6%–10%). Most invasive buzz‐pollinated plants are genetically self‐compatible (97%), but only 43% can set fruit in the absence of a pollinator. Our findings highlight the importance of establishing new pollinator mutualisms for sexual reproduction. However, we identified six non‐buzzing behaviours used to extract pollen from plants with poricidal anthers, which is important where buzzing pollinators may be absent or not attracted to newly introduced plant species.

Floral and pollinator functional diversity mediate network structure along an elevational gradient

AbstractElevational gradients in alpine ecosystems are well suited to study how plant and pollinator communities respond to climate change. In the Austrian Alps, we tested how the taxonomic and functional diversity of plants and their pollinators change with increasing elevation and how this affects plant–pollinator network structure. We measured the phenotypes of flowering plants and their pollinators and observed their interactions in 24 communities along an elevational gradient. To assess variation in floral and pollinator traits, we then quantified trait spaces (n-dimensional hypervolumes) occupied by flowers and pollinators in each community. To assess plant–pollinator network structure, we quantified the levels of complementary specialization (H2’), modularity and nestedness (weighted NODF) for each community. As elevation increased, most measures of diversity and network specialization either declined linearly or in an oscillating manner. Communities that exhibited higher pollinator functional diversity exhibited larger degrees of complementary specialization and modularity; and communities with greater floral and pollinator functional diversity and higher phylogenetic diversity were less nested. Altogether, the degree to which elevation, species diversity, functional diversity and network structure changed in conjunction suggests environmental effects on the functional and phylogenetic diversity of plants and pollinators and consequently network structure. Our results suggest that the effects of climate change on plant and pollinator community composition will impact plant–pollinator network structure and potentially pollination services at the community scale.

The evolution of flower-pollinator trait matching, and why do some alpine gingers appear to be mismatched?

Morphological matching between flower and pollinator traits has been documented in diverse plant lineages. Indeed, the matching of corolla tube length and pollinator tongue length has been cited repeatedly as a classic case of coevolution. However, there are many possible evolutionary routes to trait matching. Our aim here is both to review the evolutionary mechanisms of plant-pollinator trait matching and to investigate a specific case of trait matching/mismatching in a genus of alpine gingers. Roscoea gingers with long corolla tubes in the western Himalayas have pollinators with correspondingly long tongues, but the match between corolla tube and pollinator tongue lengths is not seen in the eastern Himalayas. Six floral traits were measured, including corolla tube depth, an internal trait controlling pollinator access to nectar. We calculated coefficients of variation and phylogenetically controlled correlation patterns of these traits in six Roscoea species in order to gain possible insights into stabilizing selection and modularization of these traits. The distal (nectar-containing) portion of the corolla tube exhibited lower coefficients of variations than did the basal portion. This is consistent with the hypothesis that pollinators mediate stabilizing selection on the distal, but not basal, portion of the corolla tube. This result, combined with phylogenetic data, suggests that the elevated liquid level of nectar in the distal tube evolved subsequent to dispersal into the eastern Himalayan region and loss of long-tongue pollinators. After accounting for phylogeny, corolla tube length, anther length, style length and labellum width were all intercorrelated. Corolla-tube depth was not part of this covariational module, however, suggesting separate adaptation to short-tongued pollinators. The reduction in functional corolla tube depth in the Roscoea appears to be related to the loss of long-tongued pollinators associated with dispersal to the eastern Himalayas and pollination by short-tongued pollinators. The apparent mismatch between floral tubes and pollinator tongues is a case of cryptic trait matching between flowers and pollinators, underscoring the importance of combining floral anatomy with pollination ecology in assessing plant-pollinator trait matching.

Pollen carryover, pollinator movement, and spatial context impact the delivery of pollination services in apple orchards.

Assessing the relative contributions of different pollinator taxa to pollination services is a central task in both basic eco-evolutionary research and applied conservation and agriculture. To that end, many studies have quantified single-visit pollen deposition and visitation frequency, which together determine a pollinator species' rate of conspecific pollen delivery. However, for plant species that require or benefit from outcrossing, pollination service quality further depends upon the ratio of outcross to self-pollen deposited, which is determined by two additional pollinator traits: pollen carryover and movement patterns among genetically compatible plant individuals. Here, we compare the pollination capacities of managed honey bees, native bumble bees, and native mining bees in apple-a varietally self-incompatible commercial crop-when pollen carryover and pollinator movement patterns are considered. We constructed simulation models of outcross pollen deposition parameterized using empirically measured single-visit pollen deposition, visitation frequency, and probabilities of intertree movement exhibited by each pollinator type, as well as pollen carryover patterns simulated based on parameters reported in the literature. In these models, we also explicitly specified the spatial relationships among cross-compatible trees based on field-realistic orchard layout schemes. We found that estimated pollination service delivery was considerably reduced for all pollinator types when pollen carryover and pollinator movement patterns were considered, as compared to when only single-visit pollen deposition and visitation frequency were considered. We also found that the performance of different pollinator types varied greatly across simulated orchard layout schemes and pollen carryover scenarios, including one instance where bumble and mining bees reversed their relative rankings. In all simulations, native bumble and mining bees outperformed managed honey bees in terms of both outcross pollen delivery per unit time and per flower visited, with disparities being greatest under scenarios of low pollen carryover. We demonstrate the degree to which pollination studies may reach inaccurate conclusions regarding pollination service delivery when pollen carryover and pollinator movement patterns are ignored. Our finding of the strong context dependence of pollination efficiency, even within a single plant-pollinator taxon pair, cautions that future studies in both basic and applied pollination biology should explicitly consider the ecological context in which pollination interactions take place.

The Relation between Flower Traits of Bitter Vetch Landraces and Potential Insect Pollinators’ Visitation

Plant–pollinator interactions research can assist in the development of more ecologically friendly crop breeding methods, leading to enhanced global food security. In the present study, we have aimed to assess fifteen floral traits as insect attractancies of six bitter vetch (Vicia ervilia (L.) Willd.) landraces, a neglected crop. Four traits related to seed yield were also measured. Abundance and foraging behavior of potential insect pollinators on bitter vetch flowers were recorded, and their species were identified. Differences among landraces regarding floral and yield traits were statistically significant in most cases. A total number of four insect species were recorded as positively visiting flowers and constituting potential pollinators of bitter vetch. At a landrace level, there was a positive correlation between potential insect pollinators’ foraging activity and the number of open flowers, especially for the landrace ERV65-Kastania, Korinthia (p ≤ 0.01). Floral tube length, as well as standard petal length, was also positively correlated in some cases with potential insect pollinator species abundance and their visitation frequency. A positive correlation was also recorded between seed yield-related traits, which varied among landraces, and potential insect pollinators’ foraging activity. The results showed that bitter vetch flowers can attract and receive positive visits from insects, despite their mainly self-pollination reproductive system. Bitter vetch flower traits, such as the number of open flowers, floral tube length, and standard petal length, could, therefore, be useful as breeding tools, aiming to develop varieties with insect pollinator-friendly traits that could lead to enhanced seed yield production and help to conserve wild insect species biodiversity in the context of sustainable agriculture.

Landscape composition and pollinator traits interact to influence pollination success in an individual‐based model

Abstract The arrangement of plant species within a landscape influences pollination via changes in pollinator movement trajectories and plant–pollinator encounter rates. Yet the combined effects of landscape composition and pollinator traits (especially specialisation) on pollination success remain hard to quantify empirically. We used an individual‐based model to explore how landscape and pollinator specialisation (degree) interact to influence pollination. We modelled variation in the landscape by generating gradients of plant species intermixing—from no mixing to complete intermixing. Furthermore, we varied the level of pollinator specialisation by simulating plant–pollinator (six to eight species) networks of different connectance. We then compared the impacts of these drivers on three proxies for pollination: visitation rate, number of consecutive visits to the focal plant species and expected number of plants pollinated. We found that the spatial arrangements of plants and pollinator degree interact to determine pollination success, and that the influence of these drivers on pollination depends on how pollination is estimated. For most pollinators, visitation rate increases in more plant mixed landscapes. Compared to the two more functional measures of pollination, visitation rate overestimates pollination service. This is particularly severe in landscapes with high plant intermixing and for generalist pollinators. Interestingly, visitation rate is less influenced by pollinator traits (pollinator degree and body size) than are the two functional metrics, likely because ‘visitation rate’ ignores the order in which pollinators visit plants. However, the visitation sequence order is crucial for the expected number of plants pollinated, since only prior visits to conspecific individuals can contribute to pollination. We show here that this order strongly depends on the spatial arrangements of plants, on pollinator traits and on the interaction between them. Taken together, our findings suggest that visitation rate, the most commonly used proxy for pollination in network studies, should be complemented with more functional metrics which reflect the frequency with which individual pollinators revisit the same plant species. Our findings also suggest that measures of landscape structure such as plant intermixing and density—in combination with pollinators' level of specialism—can improve estimates of the probability of pollination. Read the free Plain Language Summary for this article on the Journal blog.

Seasonality of pollinators in montane habitats: Cool‐blooded bees for early‐blooming plants

AbstractUnderstanding the factors that drive community‐wide assembly of plant‐pollinator systems along environmental gradients has considerable evolutionary, ecological, and applied significance. Variation in thermal environments combined with intrinsic differences among pollinators in thermal biology have been proposed as drivers of community‐wide pollinator gradients, but this suggestion remains largely speculative. We test the hypothesis that seasonality in bee pollinator composition in Mediterranean montane habitats of southeastern Spain, which largely reflects the prevalence during the early flowering season of mining bees (Andrena), is a consequence of the latter's thermal biology. Quantitative information on seasonality of Andrena bees in the whole plant community (275 plant species) and their thermal microenvironment was combined with field and laboratory data on key aspects of the thermal biology of 30 species of Andrena (endothermic ability, warming constant, relationships of body temperature with ambient and operative temperatures). Andrena bees were a conspicuous, albeit strongly seasonal component of the pollinator assemblage of the regional plant community, visiting flowers of 153 different plant species (57% of total). The proportion of Andrena relative to all bees reached a maximum among plant species which flowered in late winter and early spring, and declined precipitously from May onward. Andrena were recorded only during the cooler segment of the annual range of air temperatures experienced at flowers by the whole bee assemblage. These patterns can be explained by features of Andrena's thermal biology: null to weak endothermy; ability to forage at much lower body temperature than strongly endothermic bees (difference ~ 10°C); low upper tolerable limit of body temperature, beyond which thermal stress presumably precluded foraging at the warmest period of year; weak thermoregulatory capacity; and high warming constant enhancing ectothermic warming. Our results demonstrate the importance of lineage‐specific pollinator traits as drivers of seasonality in community‐wide pollinator composition; show that exploitation of cooler microclimates by bees does not require strong endothermy; and suggest that intense endothermy and precise thermoregulation probably apply to a minority of bees. Medium‐ and large‐sized bees with low upper thermal limits and weak thermoregulatory ability can actually be more adversely affected by climate warming than large, hot‐blooded, extremely endothermic species.

Trait‐based effects of plant invasion on floral resources, hoverflies and bees

AbstractPlant invasions can lead to homogeneous communities with decreased functional diversity. However, invasive plants, with various morphological and phenological traits, may drive pollinator communities in a less predictable, more complex way. They can promote pollinators compatible with their floral traits, while leaving others without foraging resources. Our observational study on 10 invasive herbaceous species applied a trait‐based approach to investigate plant invasion‐driven changes in floral resources, hoverfly and bee communities. We sampled invaded and non‐invaded (control) sites before and during the flowering of the invasive plants. We analysed the differences in floral traits between invasive and native plants, functional diversity and trait distributions of flower and pollinator communities between the invaded and control sites. Five invasive plant species differed from natives in floral traits. Plant invasion caused species‐specific changes in functional diversity and trait distributions of communities. For instance, invaded sites had a decreased functional diversity of hoverflies before flowering of invasive species, and larger hoverflies during flowering of invasive species compared with control sites. Smaller bees were associated with invasive plants with shallow flowers, while larger and long‐tongued bees were associated with two invasive species with restricted floral access. Similar to previous studies, pollinator traits showed mixed or neutral responses to plant invasion. This is probably due to the high integration capability of invasive plants into plant‐pollinator systems, or limitations in sampling, trait resolution, and unrevealed environmental factors. We provide recommendations for future studies to better understand the trait‐based community composition of flowering plants and pollinators.

The pollen virome: A review of pollen-associated viruses and consequences for plants and their interactions with pollinators.

The movement of pollen grains from anthers to stigmas, often by insect pollinator vectors, is essential for plant reproduction. However, pollen is also a unique vehicle for viral spread. Pollen-associated plant viruses reside on the outside or inside of pollen grains, infect susceptible individuals through vertical or horizontal infection pathways, and can decrease plant fitness. These viruses are transferred with pollen between plants by pollinator vectors as they forage for floral resources; thus, pollen-associated viral spread is mediated by floral and pollen grain phenotypes and pollinator traits, much like pollination. Most of what is currently known about pollen-associated viruses was discovered through infection and transmission experiments in controlled settings, usually involving one virus and one plant species of agricultural or horticultural interest. In this review, we first provide an updated, comprehensive list of the recognized pollen-associated viruses. Then, we summarize virus, plant, pollinator vector, and landscape traits that can affect pollen-associated virus transmission,infection, and distribution. Next, we highlight the consequences of plant-pollinator-virus interactions that emerge in complex communities of co-flowering plants and pollinator vectors, such as pollen-associated virus spread between plant species and viral jumps from plant to pollinator hosts. We conclude by emphasizing the need for collaborative research that bridges pollen biology, virology, and pollination biology.

Scale‐dependent effects of landscape structure on pollinator traits, species interactions and pollination success

The environmental filtering of species traits can influence the identity of their interaction partners and the contribution of species interactions to ecosystem functioning, but the extent to which this process is influenced by landscape composition and configuration remains unclear. We combined a field experiment with an agent‐based model to assess how landscape structure and local flower patch isolation affect pollinator body‐size distribution and plant–pollinator interactions, sampled at different spatial extents. We then evaluated how these changes in pollinator functional (i.e. body‐size) diversity influence plant reproduction. We observed higher pollinator functional diversity in less‐isolated patches, which promoted plant reproduction via a relationship between functional diversity and interaction complementarity. This complementarity occurred partly because larger pollinators interacted with more plant species. Moreover, we showed that patch configuration at the landscape level can change the direction of these local‐scale patch isolation effects on pollinator body‐size distribution, functional diversity and plant–pollinator interactions. Importantly, these relationships were robust to sampling spatial extent. Thus, management strategies to promote pollination should account for local resources and landscape structure, because response, effect and interaction traits like body size connect landscape filtering effects with local community responses and outcomes of interaction‐based functions.

Evaluation of pollination traits important for hybrid wheat development in Great Plains germplasm

AbstractHybrid wheat (Triticum aestivum L.) offers potential yield advantages over conventional inbred cultivars. For hybrid wheat to be a commercial success, the cost to produce the hybrid seed needs to be minimized. Although wheat is naturally self‐pollinated, hybrid wheat seed production can be improved by increasing the amount and availability of pollen for cross‐pollination. This research examined 19 pollination traits using the Hard Winter Wheat Association Mapping Panel for 3 years. Anther extrusion, pollen 50 date (date at which a genotype has 50% of spikes pollinating), plant height, and pollination duration (last spike pollen 50 date minus first spike pollen 50 date) were identified as the most important traits for hybrid seed production. Anther extrusion, plant height, and pollen 50 date varied widely among genotypes, while pollination duration had significant genotypic differences in one year of testing. These traits also had significant genotype × year interactions, but better and poorer performers were consistent among years. Anther extrusion was weakly, negatively correlated with plant height, and high anther extrusion semi‐dwarf genotypes were identified. Pollination duration was reduced in a high temperature (>30°C) environment, and genotypic differences in pollination duration were identified only in a milder temperature (24°C) environment. Hierarchical clustering suggested that excellent pollinator genotypes with high anther extrusion and longer pollination duration tended to pollinate early and were of short to moderate stature. Pollination traits were higher when temperatures were mild, which benefited early genotypes because they pollinated before higher temperatures limited their pollination duration.

Analysis of trait-performance-fitness relationships reveals pollinator-mediated selection on orchid pollination traits.

The role of pollinators in evolutionary floral divergence has spurred substantial effort into measuring pollinator-mediated phenotypic selection and its variation in space and time. For such estimates, the fitness consequences of pollination processes must be separated from other factors affecting fitness. We built a fitness function linking phenotypic traits of food-deceptive orchids to female reproductive success by including pollinator visitation and pollen deposition as intermediate performance components and used the fitness function to estimate the strength of pollinator-mediated selection through female reproductive success. We also quantified male performance as pollinarium removal and assessed similarity in trait effects on male and female performance. The proportion of plants visited at least once by an effective pollinator was moderate to high, ranging from 53.7% to 85.1%. Tall, many-flowered plants were often more likely to be visited and pollinated. Given effective pollination, pollen deposition onto stigmas tended to be more likely for taller plants. Pollen deposition further depended on traits affecting the physical fit of pollinators to flowers (flower size, spur length), though the exact relationships varied in time and space. Using the fitness function to assess pollinator-mediated selection through female reproductive success acting on multiple traits, we found that selection varied detectably among taxa after accounting for sampling uncertainty. Across taxa, selection on most traits was stronger on average and more variable when pollination was less reliable. These results support pollination-related trait-performance-fitness relationships and thus pollinator-mediated selection on traits functionally involved in the pollination process.

What makes a good pollinator? Relationship between pollinator traits and pollination effectiveness in apple flowers

What makes a good pollinator? Relationship between pollinator traits and pollination effectiveness in apple flowers

Combination of organic farming and flower strips in agricultural landscapes – A feasible method to maximise functional diversity of plant traits related to pollination

Agri-environment schemes (AES) are valuable instruments to support pollination in agricultural landscapes. Evaluating AES based on their effects on pollinators has high practical relevance for agricultural production and nature conservation. In our two-year assessment, we studied the effectiveness of two AES (organic farming vs flower strips) on plant traits associated with pollinator attraction (flower size, colour, and ultraviolet pattern) and reward accessibility (flowering duration, and nectar quantity). We selected ten landscapes along a landscape-scale field size gradient in Central Germany. Three types of winter wheat fields (organic, and conventional fields with and without flower strips) were chosen in each landscape. We sampled the vegetation in transects designated in characteristic field parts, i.e. grassy margins, field edges (or flower strips), and field interiors in the growing seasons of 2016 and 2017. We calculated community-weighted means and functional diversity of plant traits and tested the effects of field size, management, and within-field position with linear mixed-effects models. We showed that organic fields and flower strips provided more abundant and functionally more diverse flowers than conventional fields. Flower strips were superior with the highest insect-pollinated plant cover and the highest ratio of plants with flowers showing ultraviolet patterns. Although grassy margins next to flower strips harboured twice as many species as those without flower strips, this positive effect did not emerge in conventional field interiors. Landscape configuration expressed as mean field size did not affect pollination traits in our study. Our results highlighted that both organic farming and flower strips maintained abundant and functionally diverse insect-pollinated flora, and thus they can potentially support larger pollinator communities. However, only organic farming could maintain high functional diversity of pollination-related plant traits in field interiors. Hence flower strips and organic farming in combination might be a good option for sustaining diverse pollinator communities and their services. • Organic fields and annual wildflower strips can boost pollinator-friendly flora. • Plant pollination trait diversity is high in both agro-environmental schemes. • Both schemes can supposedly maintain high pollination ecosystem service. • There is little spill-over from flower strips to intensive field interiors. • Plant functional diversity of grassy field margins benefited from flower strips.

Phenotypic integration of pollination traits in a distylous species with high intra-individual floral variation

Phenotypic integration of pollination traits in a distylous species with high intra-individual floral variation

Hold tight or loosen up? Functional consequences of a shift in anther architecture depend substantially on bee body size.

A fundamental question in pollination ecology is how pollinators affect the evolution of different floral forms. Yet functional effects of shifts in floral form for plant and pollinator are frequently unclear. For instance, flowers that conceal pollen within tube-like anthers that are spread apart and move freely (free architecture) or are tightly joined together (joined architecture) have evolved independently across diverse plant families and are geographically widespread. Surprisingly, how their bee pollinators affect the function of both architectures remains unknown. We hypothesised that bee body size would affect foraging success and pollination differently for free and joined anther architectures. Therefore, we modified the anther architecture of a single plant species (Solanum elaeagnifolium) and used a single species of generalist bumble bee (Bombus impatiens), which varies greatly in body size. We found that on free anther architecture, larger bees were better pollinators. More pollen on their bodies was available for pollination and they deposited more pollen on stigmas. Conversely, on joined anther architecture, smaller bees were better pollinators. They collected less pollen into their pollen baskets, had more pollen on their bodies available for pollination, and deposited more pollen on stigmas. While we also found modest evidence that plants benefit more from joined versus free anther architecture, further investigation will likely reveal this also depends on pollinator traits. We discuss potential mechanisms by which pollinator size and anther architecture interact and implications for floral evolution.

Assessing ecological interactions in urban areas using citizen science data: Insights from hummingbird–plant meta-networks in a tropical megacity

Urbanization is one of the most intensive threats to biodiversity worldwide. The rapid sprawl of urban settings often comprises a drastic landscape transformation due to the replacement of natural vegetation by impervious surfaces. However, cities can serve as critical refuges for some native fauna, particularly for pollinators. Here we used citizen data to contrast the structure of hummingbird-plant meta-networks across different greenspaces (natural protected areas, urban parks, urban gardens and street trees areas) in a tropical megacity. We compiled hummingbird-plant visitation records in Mexico City available in two citizen science resources: iNaturalist and eBird. We first determined whether the retrieved dataset was representative to estimate network metrics by calculating sample coverage and estimating species richness in different greenspaces. Then, we characterized network structure and plant importance for network organization according to plant origin, life form and pollination syndrome. We recorded 17 hummingbirds visiting 84 plant species, encompassing a total of 742 interactions. Natural protected areas and urban parks showed a higher richness of hummingbirds and plants. All networks had low levels of connectance, specialization, and nestedness. Modularity was significant across all networks with higher values in natural protected areas and urban gardens. Native and introduced plant species showed a similar contribution to network organization. Non-ornithophilous plants were most important in natural protected areas, while tree species were most important in street trees greenspaces. Our results provide evidence of generalization of hummingbird-plant networks in urban areas. Introduced species and non-ornithophilous plants were equally important for hummingbirds, suggesting an integration of alien plants with no specialized bird pollination traits into ecological networks in urban scenarios. Promoting conservation initiatives as pollinator gardens with key native species for hummingbirds across the city could contribute to the functional connectivity and restoration of ecological interactions in cities.

Division of foraging behaviour: Assessments of pollinator traits when visiting a model plant species

Diverse animals visit flowers but not all engage in pollination, and only behaviours involving stigmal contact result in successful pollination events. Ethological indices developed for sociobiological contexts (caste evolution) have unrealized potential to provide insights on pollination services but have not been applied in this context before. In the present study, we characterized foraging behaviours as functional traits, which allowed us to predict whether ecosystems services are robust to species-specific trait loss. We aimed to (1) document the variety, duration and frequency of on-flower behaviours, (2) determine which taxa engage in stigmal contact and (3) investigate vulnerabilities of pollination service to loss of pollinator taxa. We used video recordings to document on-flower behaviours of animals visiting a single apple cultivar (Malus domestica var. ‘Pink Lady’), which removed confounding factors to enable a robust assessment of functional pollination behaviour. We adapted division of labour statistics (designed to assess caste-specific behavioural task fidelity within social insect colonies) to investigate taxon-specific foraging behaviours within this assemblage of pollinators – a novel application. An ethogram of 11 behaviours was derived from 19,518 min of observations (2350 visits; 19 taxa). Most (53%) flower visits involved stigmal contact (termed ‘contact visits’), but the percentage of contact visits varied between taxa. We introduce division of foraging behaviour (DFB) indices – which imply the focal pollinator assemblage consists of a mix of behaviourally generalized and specialized taxa with a slight bias towards specialization: division of taxa into behaviours DFBY|X = 0.59; division of behaviours into taxa DFBX|Y = 0.76. Simulated extinction of taxa from this insect assemblage significantly shifted DFBY|X in four instances. These qualitative assessments of behavioural traits imply moderate functional redundancy in pollination services provided by 11 insect taxa to a model plant, even under simulated extinction events, suggesting pollination services may be somewhat resilient to animal–plant network disruptions in this Australian agroecological study system.

Functional traits of plants and pollinators explain resource overlap between honeybees and wild pollinators

Managed and wild pollinators often cohabit in both managed and natural ecosystems. The western honeybee, Apis mellifera, is the most widespread managed pollinator species. Due to its density and behaviour, it can potentially influence the foraging activity of wild pollinators, but the strength and direction of this effect are often context-dependent. Here, we observed plant–pollinator interactions in 51 grasslands, and we measured functional traits of both plants and pollinators. Using a multi-model inference approach, we explored the effects of honeybee abundance, temperature, plant functional diversity, and trait similarity between wild pollinators and the honeybee on the resource overlap between wild pollinators and the honeybee. Resource overlap decreased with increasing honeybee abundance only in plant communities with high functional diversity, suggesting a potential diet shift of wild pollinators in areas with a high variability of flower morphologies. Moreover, resource overlap increased with increasing trait similarity between wild pollinators and the honeybee. In particular, central-place foragers of family Apidae with proboscis length similar to the honeybee exhibited the highest resource overlap. Our results underline the importance of promoting functional diversity of plant communities to support wild pollinators in areas with a high density of honeybee hives. Moreover, greater attention should be paid to areas where pollinators possess functional traits similar to the honeybee, as they are expected to be more prone to potential competition with this species.