Loss of habitats and native species, introduction of invasive species, and changing climate regimes lead to the homogenization of landscapes and communities, affecting the availability of habitats ...and resources for economically important guilds, such as pollinators. Understanding how pollinators and their interactions vary along resource diversity gradients at different scales may help to determine their adaptability to the current diversity loss related to global change. We used data on 20 plant–pollinator communities along gradients of flower richness (local diversity) and landscape heterogeneity (landscape diversity) to understand how the diversity of resources at local and landscape scales affected (1) wild pollinator abundance and richness (accounting also for honey bee abundance), (2) the structure of plant–pollinator networks, (3) the proportion of actively selected interactions (those not occurring by neutral processes), and (4) pollinator diet breadth and species' specialization in networks. Wild pollinator abundance was higher overall in flower‐rich and heterogeneous habitats, while wild pollinator richness increased with flower richness (more strongly for beetles and wild bees) and decreased with honeybee abundance. Network specialization (H2′), modularity, and functional complementarity were all positively related to floral richness and landscape heterogeneity, indicating niche segregation as the diversity of resources increases at both scales. Flower richness also increased the proportion of actively selected interactions (especially for wild bees and flies), whereas landscape heterogeneity had a weak negative effect on this variable. Overall, network‐level metrics responded to larger landscape scales than pollinator‐level metrics did. Higher floral richness resulted in a wider taxonomic and functional diet for all the study guilds, while functional diet increased mainly for beetles. Despite this, specialization in networks (d′) increased with flower richness for all the study guilds, because pollinator species fed on a narrower subset of plants as communities became richer in species. Our study indicates that pollinators are able to adapt their diet to resource changes at local and landscape scales. However, resource homogenization might lead to poor and generalist pollinator communities, where functionally specialized interactions are lost. This study highlights the importance of including different scales to understand the effects of global change on pollination service through changes in resource diversity.
Conservation areas established in agricultural fields can provide habitat for native organisms, but they also have the potential to accumulate and expose organisms to insecticides. Prairie strips are ...zones of cropland that have been converted to native prairie vegetation. Prairie strips increase biodiversity and reduce nutrient runoff, but they may also accumulate insecticides that endanger visiting organisms or facilitate the movement of insecticides across the landscape. In a study of paired catchments with ongoing neonicotinoid inputs, we measured the impact of prairie strips (10 % of cropland) on the accumulation and movement of the neonicotinoid insecticide clothianidin (CLO) into surface soil, deep soil, plant tissue, and groundwater across multiple slope positions during three phases of a maize growing season. While CLO accumulates in maize leaf tissue midseason following neonicotinoid application, we did not find evidence that prairie plant species in prairie strips accumulate CLO at concentrations lethal to pollinator insects. We also found that downslope soils contained the highest CLO concentrations in both catchments, showing that prairie strips did not eliminate downslope insecticide runoff. Our study adds to the existing literature examining prairie strip effects on downslope agrochemical transport, showing that when prairie strips are planted in cropland with ongoing neonicotinoid inputs, they can provide safe, low-insecticide habitat for visiting organisms amidst their other services, but may not reduce offsite insecticide runoff.
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•We measured neonicotinoids in two catchments with ongoing neonicotinoid inputs.•Prairie strips contained lower plant and soil neonicotinoids than cropland.•Plants in prairie strips contained neonicotinoid levels nonlethal to pollinators.•Planting prairie strips in a neonicotinoid-treated field did not reduce runoff.•Prairie strips did not change neonicotinoid levels in surrounding maize leaf tissue.
Summary
Pollinators utilize floral resources that vary in colour, scent and reward quality. Variation in such traits, including nectar rewards, in addition to cues associated with their quality, can ...influence pollinator foraging decisions with consequences for pollinator reproductive success. Nectar is commonly subject to colonization by micro‐organisms capable of affecting a suite of traits important for pollinator attraction and fitness; yet, links between microbial presence and changes in pollinator preference and performance remain few.
Here, we evaluated the effects of a nectar‐inhabiting micro‐organism on pollinator foraging behaviour and reproduction using the common eastern bumblebee Bombus impatiens and the cosmopolitan nectar yeast Metschnikowia reukaufii. Using a combination of choice and no‐choice behavioural and feeding assays, we manipulated the presence and viability of M. reukaufii in nectar and assessed bumblebee foraging and reproductive responses.
Bombus impatiens workers responded positively to the presence of yeasts. Foragers trained to associate yeast presence with flower colour visited a significantly greater proportion of flowers inoculated with yeast when subject to a colour discrimination test. Moreover, foragers naïve to nectar yeasts incorporated more yeast‐inoculated flowers into initial foraging bouts when presented with a novel floral array. In addition, bees spent significantly longer foraging on yeast‐inoculated flowers compared to yeast‐free flowers. However, when we manipulated yeast presence and viability in microcolonies of queenless workers, we found no effect of yeast on components of bumblebee reproduction, such as initiation of egg laying and number of eggs laid. This lack of an effect of yeast persisted even under conditions of pollen limitation.
Taken together, these results suggest that nectar yeasts can enhance floral signalling and alter pollinator foraging behaviour at individual flowers, though they may not directly affect pollinator performance. Thus, nectar yeasts may play a significant role in mediating pollinator foraging behaviour, with consequences for plant fitness and evolution of floral traits.
Lay Summary
Premise
Floral traits are frequently under pollinator‐mediated selection, especially in taxa subject to strong pollen‐limitation, such as those reliant on pollinators. However, antagonists can be ...agents of selection on floral traits as well. The causes of selection acting on spring ephemerals are understudied though these species can experience particularly strong pollen‐limitation. I examined pollinator‐ and antagonist‐mediated selection in a narrowly endemic spring ephemeral, Trillium discolor.
Methods
I measured pollen limitation in T. discolor across two years and evaluated its breeding system. I compared selection on floral traits (display height, petal size, petal color, flowering time) between open‐pollinated, and pollen‐supplemented plants to measure the strength and mode of pollinator‐mediated selection. I assessed whether natural levels of antagonism impacted selection on floral traits.
Results
Trillium discolor was self‐incompatible and experienced pollen limitation in both years of the study. Pollinators exerted negative disruptive selection on display height and petals size. In one year, pollinator‐mediated selection favored lighter petals but in the second year pollinators favored darker petals. Antagonist damage did not alter selection on floral traits.
Conclusions
Results demonstrate that pollinators mediate the strength and mode of selection on floral traits in T. discolor. Interannual variation in the strength, mode, and direction of pollinator‐mediated selection on floral traits could be important for maintaining of floral diversity in this system. Observed levels of antagonism were weak agents of selection on floral traits.
Residential gardens are a valuable habitat for insect pollinators worldwide, but differences in individual gardening practices substantially affect their floral composition. It is important to ...understand how the floral resource supply of gardens varies in both space and time so we can develop evidence‐based management recommendations to support pollinator conservation in towns and cities.
We surveyed 59 residential gardens in the city of Bristol, UK, at monthly intervals from March to October. For each of 472 garden surveys, we combined floral abundances with nectar sugar data to quantify the nectar production of each garden, investigating the magnitude, temporal stability, and diversity and composition of garden nectar supplies.
We found that individual gardens differ markedly in the quantity of nectar sugar they supply (from 2 to 1,662 g), and nectar production is higher in more affluent neighbourhoods, but not in larger gardens. Nectar supply peaks in July (mid‐summer), when more plant taxa are in flower, but temporal patterns vary among individual gardens. At larger spatial scales, temporal variability averages out through the portfolio effect, meaning insect pollinators foraging across many gardens in urban landscapes have access to a relatively stable and continuous supply of nectar through the year.
Turnover in species composition among gardens leads to an extremely high overall plant richness, with 636 taxa recorded flowering. The nectar supply is dominated by non‐natives, which provide 91% of all nectar sugar, while shrubs are the main plant life form contributing to nectar production (58%). Two‐thirds of nectar sugar is only available to relatively specialised pollinators, leaving just one‐third that is accessible to all.
Synthesis and applications. By measuring nectar supply in residential gardens, our study demonstrates that pollinator‐friendly management, affecting garden quality, is more important than the size of a garden, giving every gardener an opportunity to contribute to pollinator conservation in urban areas. For gardeners interested in increasing the value of their land to foraging pollinators, we recommend planting nectar‐rich shrubs with complementary flowering periods and prioritising flowers with an open structure in late summer and autumn.
By measuring nectar supply in residential gardens, our study demonstrates that pollinator‐friendly management, affecting garden quality, is more important than the size of a garden, giving every gardener an opportunity to contribute to pollinator conservation in urban areas. For gardeners interested in increasing the value of their land to foraging pollinators, we recommend planting nectar‐rich shrubs with complementary flowering periods and prioritising flowers with an open structure in late summer and autumn.
Alpine environments are among the habitats most strongly affected by climate change, and consequently their unique plants and pollinators are faced with the challenge of adapting or going extinct. ...Changes in temperature and precipitation affect snowpack and snowmelt, resulting in changes in the growing season in this environment where plant growth and pollinator activity are constrained to the snow‐free season, which can vary significantly across the landscape if there is significant topographic complexity. As in other ecosystems, the resulting changes in phenology are not uniform among species, creating the potential for altered and new interspecific interactions. New plant and animal species are arriving as lower altitude species move up with warming temperatures, introducing new competitors and generating changes in plant–pollinator interactions. Repeating historical surveys, taking advantage of museum collections, and using new technology will facilitate our understanding of how plants and pollinators are responding to the changing alpine environment.
Gardens are important habitats for pollinators, providing floral resources and nesting sites. There are high levels of public support for growing ‘pollinator‐friendly’ plants but while plant ...recommendation lists are available, they are usually inconsistent, poorly supported by scientific research and target a narrow group of pollinators. In order to supply the most appropriate resources, there is a clear need to understand foraging preferences, for a range of pollinators, across the season within horticultural landscapes.
Using an innovative DNA metabarcoding approach, we investigated foraging preferences of four groups of pollinators in a large and diverse, horticultural and agricultural landscape, across the flowering season and over 2 years, significantly improving on the spatial and temporal scale that can be achieved using observational studies.
Bumblebees, honeybees, non‐corbiculate bees and hoverflies visited 191 plant taxa. Overall floral resources were shared between the different types of pollinators, but significant differences were seen between the plants used most abundantly by bees (Hymenoptera) and hoverflies (Diptera).
Floral resource use by pollinators is strongly associated with seasonal changes in flowering plants, with pollinators relying on dominant plants found within each season, with preferences consistent across both years.
The plants identified were categorised according to their native status to investigate the value of native and non‐native plants. The majority of floral resources used were of native and near‐native origin, but the proportion of horticultural and naturalised plants increased during late summer and autumn.
Synthesis and applications. Plant recommendation lists for pollinators should distinguish between bees and hoverflies and provide evidence‐based floral recommendations throughout the year that include native as well as non‐native plants for use in the United Kingdom and Northern Europe. Specific management recommendations include reducing mowing to encourage plants such as dandelion Taraxacum officinale and buttercups Ranunculus spp., and reducing scrub management to encourage bramble Rubus fruticosus.
Crynodeb
Mae gerddi'n gynefinoedd pwysig ar gyfer peillwyr, yn darparu adnoddau blodeuo a safleoedd nythu. Mae llawer iawn o gefnogaeth gan y cyhoedd i dyfu planhigion sy'n “garedig i beillwyr”, ond er bod rhestrau ar gael o blanhigion sy'n ‘garedig i beillwyr’ yn cael eu hargymell, maen nhw fel rheol yn anghyson, heb lawer o ymchwil wyddonol yn sail iddynt, ac yn targedu grŵp cyfyng o beillwyr. Er mwyn darparu'r adnoddau mwyaf priodol, mae angen amlwg i ddeall dewisiadau fforio, ar gyfer amrywiaeth o beillwyr ar draws y tymhorau ac o fewn amgylcheddau gardd.
Gan ddefnyddio dull meta‐barcodio DNA arloesol, rydym wedi bod yn archwilio dewisiadau fforio pedwar grŵp o beillwyr mewn tirwedd garddio mawr ac amrywiol, ar draws y tymhorau blodeuo a thros ddwy flynedd. Mae hyn wedi gwella'n sylweddol y raddfa o ran lle ac amser y gellir ei sicrhau drwy ddefnyddio astudiaethau arsylwi.
Daeth cacwn, gwenyn mêl, gwenyn heb beillgodau a phryfed hofran i ymweld â 191 tacson. Cafodd adnoddau blodeuo cyffredinol eu rhannu rhwng y gwahanol fathau o beillwyr, ond gwelwyd gwahaniaethau sylweddol rhwng y planhigion a ddefnyddiwyd fwyaf gan wenyn (Hymenoptera) a phryfed hofran (Diptera).
Mae cysylltiad cryf rhwng yr adnoddau blodeuo a ddefnyddir gan beillwyr a newidiadau tymhorol mewn planhigion sy'n blodeuo. Mae peillwyr yn dibynnu ar y planhigion mwyaf amlwg ym mhob tymor, ac roedd y dewisiadau'n gyson ar draws y ddwy flynedd.
Cafodd y planhigion a nodwyd eu gosod mewn categori yn ôl eu statws brodorol i ymchwilio i werth planhigion brodorol a rhai nad ydynt yn frodorol. Roedd mwyafrif yr adnoddau blodeuo a ddefnyddiwyd yn rhai brodorol neu bron yn frodorol, ond cynyddwyd cyfran y planhigion garddwriaethol a rhai wedi cynefino yn ystod diwedd yr haf a'r hydref.
Synthesis a defnyddio. Dylai rhestrau planhigion ar gyfer peillwyr wahaniaethu rhwng gwenyn a phryfed hofran, a darparu argymhellion blodeuo'n seiliedig ar dystiolaeth drwy gydol y flwyddyn, sy'n cynnwys planhigion brodorol a rhai heb fod yn frodorol i'w defnyddio yn y Deyrnas Gyfunol a Gogledd Ewrop. Mae argymhellion rheoli penodol yn cynnwys llai o dorri gwair i annog planhigion fel dant y llew Taraxacum officinale a blodau ymenyn Ranunculus spp. a, lleihau rheoli prysgwydd i annog drain Rubus fruticosus i dyfu.
Plant recommendation lists for pollinators should distinguish between bees and hoverflies and provide evidence‐based floral recommendations throughout the year that include native as well as non‐native plants for use in the UK and Northern Europe. Specific management recommendations include reducing mowing to encourage plants such as dandelion Taraxacum officinale and buttercups Ranunculus spp., and reducing scrub management to encourage bramble Rubus fruticosus.
• The causative link between phenotypic divergence and reproductive isolation is an important but poorly understood part of ecological speciation. We studied the effects of floral-tube length ...variation on pollen placement/receipt positions and reproductive isolation.
• In a population of Lapeirousia anceps (Iridaceae) with bimodal floral-tube lengths, we labelled pollen of short- and long-tubed flowers with different colour fluorescent nanoparticles (quantum dots). This enabled us to map pollen placement by long- and short-tubed flowers on the only floral visitor, a long-proboscid fly. Furthermore, it allowed us to quantify pollen movement within and between short- and long-tubed flowers.
• Short- and long-tubed flowers placed pollen on different parts of the pollinator, and long-tubed flowers placed more pollen per visit than short-tubed flowers. This resulted in assortative pollen receipt (most pollen received comes from the same phenotype) and strong but asymmetric reproductive isolation, where short-tubed plants are more reproductively isolated than long-tubed plants.
• These results suggest that floral-tube length divergence can promote mechanical isolation in plants through divergence in pollen placement sites on pollinators. Consequently, in concert with other reproductive isolation mechanisms, selection for differences in floral-tube length can play an important role in ecological speciation of plants.
1 Multiple-species floral displays have been hypothesized to facilitate pollination by attracting a greater number and/or diversity of pollinators. Here I present experimental confirmation of ...pollination facilitation among coflowering plants that have morphologically distinct flowers. 2 Pollinator visits to Raphanus raphanistrum, a self-incompatible herbaceous plant, increased when it occurred with one or a combination of Cirsium arvense, Hypericum perforatum and Solidago canadensis than when it occurred alone. 3 Enhanced visitation to R. raphanistrum in mixed species plots was reflected by increased seed production. 4 Facilitative effects in pollination were conditional on the density and evenness of the floral mixture and graded into competition as the relative abundance of R. raphanistrum declined in a two-species mixture. 5 Previously proposed mechanisms for facilitative interactions cannot explain facilitation among florally distinct plant displays. An alternative mechanism of differential but complementary floral rewards is proposed to explain facilitative attraction of pollinators. 6 Facilitation of, and competition for, pollination has implications for regeneration by seed of rare or isolated plants, and of mitigating Allee effects that afflict such populations.
The western honey bee (Apis mellifera) is the most frequent floral visitor of crops worldwide, but quantitative knowledge of its role as a pollinator outside of managed habitats is largely lacking. ...Here we use a global dataset of 80 published plant–pollinator interaction networks as well as pollinator effectiveness measures from 34 plant species to assess the importance of A. mellifera in natural habitats. Apis mellifera is the most frequent floral visitor in natural habitats worldwide, averaging 13% of floral visits across all networks (range 0–85%), with 5% of plant species recorded as being exclusively visited by A. mellifera. For 33% of the networks and 49% of plant species, however, A. mellifera visitation was never observed, illustrating that many flowering plant taxa and assemblages remain dependent on non-A. mellifera visitors for pollination. Apis mellifera visitation was higher in warmer, less variable climates and on mainland rather than island sites, but did not differ between its native and introduced ranges. With respect to single-visit pollination effectiveness, A. mellifera did not differ from the average non-A. mellifera floral visitor, though it was generally less effective than the most effective non-A. mellifera visitor. Our results argue for a deeper understanding of how A. mellifera, and potential future changes in its range and abundance, shape the ecology, evolution, and conservation of plants, pollinators, and their interactions in natural habitats.
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