Landscape impacts on pollinator communities in temperate systems: evidence and knowledge gaps

Trace Metals in Nectar of Important Urban Pollinator Forage Plants: A Direct Exposure Risk to Pollinators and Nectar-Feeding Animals in Cities

Pollinators are exposed to metals while foraging in the landscape and accumulate detectable concentrations of trace metals within their bodies, although major exposure routes remain unclear. As nectar is the main source of food for pollinators, we analyzed trace metal content within floral rewards to identify if nectar contained detectable metals and may serve as an oral exposure route. Nectar from flowering plant species growing within vacant lots in the city of Cleveland, OH, USA was extracted using a centrifuge and tested for the metals arsenic, cadmium, chromium, and lead using ICP-MS. We collected volunteer flower species that are common pollinator forage plants. Nectar metal content varied by plant and metal species, but not by location. Nectar arsenic concentrations ranged from 0 to 8.44 μg/L, cadmium from 0 to 32.99 μg/L, chromium from 0 to 45.69 μg/L, and lead from 0 to 135.31 μg/L. The presence of these soil contaminants in nectar indicates that the uptake and concentration of metals within nectar resources is likely a major route of metal exposure for pollinators and nectar-feeding animals.

Bumblebee Abundance in Species-Rich Grasslands in Southern Sweden Decreases with Increasing Amount of Arable Land at a Landscape Level

Conservation of bumblebee populations is essential because of their role as pollinators. Declines in bumblebee abundance have been documented in recent decades, mostly attributed to agricultural intensification, landscape simplification and loss of semi-natural grasslands. In this study, we investigated the effects of landscape composition on bumblebee abundance at different spatial scales in 476 semi-natural grassland sites in southern Sweden. The area of arable land had a negative effect on total bumblebee abundance at all scales. This was most pronounced for short-tongued bumblebees, species typical of forested landscapes, and species with medium to large colony sizes and early queen emergence. The area of semi-natural grassland had a clear negative effect up to 1 km, affecting short-tongued bumblebees in both forested and agricultural landscapes and species with medium colony sizes and early queen emergence. The negative effect of arable land on bumblebees calls for action to adapt farming practices to ensure their conservation, e.g., by reducing pesticide use, improving crop diversity and promoting the presence of floral resources and alternative bumblebee habitats, such as species-rich field margins.

Landscape structure affects temporal dynamics in the bumble bee virome: Landscape heterogeneity supports colony resilience

Virus spillovers from managed honey bees, Apis mellifera, are thought to contribute to the decline of wild pollinators, including bumble bees. However, data on the impact of such viruses on wild pollinators remain scarce, and the influence of landscape structure on virus dynamics is poorly understood. In this study, we deployed bumble bee colonies in an agricultural landscape and studied changes in the bumble bee virome during field placement under varying habitat composition and configuration using a multiscale analytical framework. We estimated prevalence of viruses and viral loads (i.e. number of viral genomic equivalent copies) in bumble bees before and after placing them in the field using next generation sequencing and quantitative PCR. The results show that viral loads and number of different viruses present increased during placement in the field and that the virus composition of the colonies shifted from an initial dominance of honey bee associated viruses to a higher number (in both viral loads and number of viruses present) of bumble bee associated viruses. Especially DWV-B, typical for honey bees, drastically decreased after the time in the field. Viral loads prior to placing colonies in the field showed no effect on colony development, suggesting low impacts of these viruses in field settings. Notably, we further demonstrate that increased habitat diversity results in a lower number of different viruses present in Bombus colonies, while colonies in areas with well-connected farmland patches decreased in their total viral load after field placement. Our results emphasize the importance of landscape heterogeneity and connectivity for wild pollinator health and that these influences predominate at fine spatial scales.

Bees in the city: Findings from a scoping review and recommendations for urban planning

Over the last decades, bee biodiversity has dropped sharply due to land use change, including urbanization. To contrast this, recent research has pointed to cities as a hotspot for bees. Because of this ambiguity, a scoping review has been conducted to examine the urban characteristics that impact bees and how bees are impacted. A total of 276 articles were analyzed against landscape and local habitat characteristics. The key findings include first that natural areas are more valuable for bees since biodiversity levels are higher. Second, urban areas generally score better than agricultural and rural areas. Third, plant biodiversity positively influences bee biodiversity. Fourth, the urban environment strongly affects some bee traits and the proportion of native bees. For making cities bee friendly and bee inclusive, we recommend to maintain natural areas, connect natural areas to urban ecosystems, encourage floral abundance and diversity and increasing the size of urban green areas overall.

Stable gullies provide a suitable habitat for functional insects and reduce the threat of pests on crops in farmland of Northeast China

Gullies with lower altitudes compared to the surrounding environment are widely distributed in farmland of the watershed and their numbers are still expanding. However, it is still unclear how these gullies regulate the functional insects in farmland. In this study, land use types combined with the herbaceous plant, herbicide application, soil moisture, topography and climatic factors during crop growth were considered to understand how gullies influence the dynamics of functional insects in farmland from a watershed (240 ha) of Northeast China. The primary findings demonstrate that the richness and abundance of functional insects are generally greatest in gullies, particularly in stable gullies, and decrease in the following order: forest belts, grasslands, and farmlands within the watershed. Notably, the ratios of beneficial insects to pests (BI/Pest) in terms of richness and abundance were lower in gullies before July but reversed after July, in comparison to farmland. Stable gullies exhibited higher BI/Pest abundance and diversity ratios than developing gullies. The richness and abundance of functional insects were higher in the middle sections of gullies compared to their heads and tails. Furthermore, the ratios of BI/Pest were generally lower in farmlands than in any gully position. Functional insect dynamics were mainly determined by season, followed by plant abundance and biomass in the gullies, and rarely by soil moisture in the both watershed and single gullies scales. Generally, the richness and abundance of functional insects in farmland were mainly influenced by gullies, especially influenced by the gully middle position. Insect composition in farmland influenced by stable gullies was stronger than by developing gullies, and stable gullies were more beneficial in reducing the threat of pests to crops in the farmland of the watershed.

Pollinator-mediated effects of landscape-scale land use on grassland plant community composition and ecosystem functioning - seven hypotheses

Environmental change is disrupting mutualisms between organisms worldwide. Reported declines in insect populations and changes in pollinator community compositions in response to land use and other environmental drivers have put the spotlight on the need to conserve pollinators. While this is often motivated by their role in supporting crop yields, the role of pollinators for reproduction and resulting taxonomic and functional assembly in wild plant communities has received less attention. Recent findings suggest that observed and experimental gradients in pollinator availability can affect plant community composition, but we know little about when such shifts are to be expected, or the impact they have on ecosystem functioning. Correlations between plant traits related to pollination and plant traits related to other important ecosystem functions, such as productivity, nitrogen uptake or palatability to herbivores, lead us to expect non-random shifts in ecosystem functioning in response to changes in pollinator communities. At the same time, ecological and evolutionary processes may counteract these effects of pollinator declines, limiting changes in plant community composition, and in ecosystem functioning. Despite calls to investigate community- and ecosystem-level impacts of reduced pollination, the study of pollinator effects on plants has largely been confined to impacts on plant individuals or single-species populations. With this review we aim to break new ground by bringing together aspects of landscape ecology, ecological and evolutionary plant-insect interactions, and biodiversity-ecosystem functioning research, to generate new ideas and hypotheses about the ecosystem-level consequences of pollinator declines in response to land-use change, using grasslands as a focal system. Based on an integrated set of seven hypotheses, we call for more research investigating the putative pollinator-mediated links between landscape-scale land use and ecosystem functioning. In particular, future research should use combinations of experimental and observational approaches to assess the effects of changes in pollinator communities over multiple years and across species on plant communities and on trait distributions both within and among species.

Evolutionary plant-pollinator responses to anthropogenic land-use change: impacts on ecosystem services

Agricultural intensification at field and landscape scales, including increased use of agrochemicals and loss of semi-natural habitats, is a major driver of insect declines and other community changes. Efforts to understand and mitigate these effects have traditionally focused on ecological responses. At the same time, adaptations to pesticide use and habitat fragmentation in both insects and flowering plants show the potential for rapid evolution. Yet we lack an understanding of how such evolutionary responses may propagate within and between trophic levels with ensuing consequences for conservation of species and ecological functions in agroecosystems. Here, we review the literature on the consequences of agricultural intensification on plant and animal evolutionary responses and interactions. We present a novel conceptualization of evolutionary change induced by agricultural intensification at field and landscape scales and emphasize direct and indirect effects of rapid evolution on ecosystem services. We exemplify by focusing on economically and ecologically important interactions between plants and pollinators. We showcase available eco-evolutionary theory and plant-pollinator modelling that can improve predictions of how agricultural intensification affects interaction networks, and highlight available genetic and trait-focused methodological approaches. Specifically, we focus on how spatial genetic structure affects the probability of propagated responses, and how the structure of interaction networks modulates effects of evolutionary change in individual species. Thereby, we highlight how combined trait-based eco-evolutionary modelling, functionally explicit quantitative genetics, and genomic analyses may shed light on conditions where evolutionary responses impact important ecosystem services.

Six Steps towards a Spatial Design for Large-Scale Pollinator Surveillance Monitoring

Despite the importance of pollinators to ecosystem functioning and human food production, comprehensive pollinator monitoring data are still lacking across most regions of the world. Policy-makers have recently prioritised the development of large-scale monitoring programmes for pollinators to better understand how populations respond to land use, environmental change and restoration measures in the long term. Designing such a monitoring programme is challenging, partly because it requires both ecological knowledge and advanced knowledge in sampling design. This study aims to develop a conceptual framework to facilitate the spatial sampling design of large-scale surveillance monitoring. The system is designed to detect changes in pollinator species abundances and richness, focusing on temperate agroecosystems. The sampling design needs to be scientifically robust to address questions of agri-environmental policy at the scales of interest. To this end, we followed a six-step procedure as follows: (1) defining the spatial sampling units, (2) defining and delimiting the monitoring area, (3) deciding on the general sampling strategy, (4) determining the sample size, (5) specifying the sampling units per sampling interval, and (6) specifying the pollinator survey plots within each sampling unit. As a case study, we apply this framework to the "Wild bee monitoring in agricultural landscapes of Germany" programme. We suggest this six-step procedure as a conceptual guideline for the spatial sampling design of future large-scale pollinator monitoring initiatives.

Using individual-based trait frequency distributions to forecast plant-pollinator network responses to environmental change

Determining how and why organisms interact is fundamental to understanding ecosystem responses to future environmental change. To assess the impact on plant-pollinator interactions, recent studies have examined how the effects of environmental change on individual interactions accumulate to generate species-level responses. Here, we review recent developments in using plant-pollinator networks of interacting individuals along with their functional traits, where individuals are nested within species nodes. We highlight how these individual-level, trait-based networks connect intraspecific trait variation (as frequency distributions of multiple traits) with dynamic responses within plant-pollinator communities. This approach can better explain interaction plasticity, and changes to interaction probabilities and network structure over spatiotemporal or other environmental gradients. We argue that only through appreciating such trait-based interaction plasticity can we accurately forecast the potential vulnerability of interactions to future environmental change. We follow this with general guidance on how future studies can collect and analyse high-resolution interaction and trait data, with the hope of improving predictions of future plant-pollinator network responses for targeted and effective conservation.

DNA metabarcoding unveils the effects of habitat fragmentation on pollinator diversity, plant-pollinator interactions, and pollination efficiency in Maldive islands

Habitat fragmentation affects biodiversity, but with unclear effects on pollinators and their interactions with plants in anthropized landscapes. Islands could serve as open air laboratories, suitable to disentangle how land-use alteration impacts pollination ecology. In Maldive islands we investigated how pollinator richness, plant-pollinator interactions and pollination efficiency are influenced by the green area fragmentation (i.e., gardens and semi-natural patches). Moreover, we considered the mediating role of pollinator body size and the plant trait of being invasive in shaping interactions. To do this, we surveyed pollinator insects from 11 islands representing a gradient of green area fragmentation. A DNA metabarcoding approach was adopted to identify the pollen transported by pollinators and characterize the plant-pollinator interactions. We found that intermediate levels of green area fragmentation characterized pollinator communities and increased their species richness, while decreasing interaction network complexity. Invasive plants were more frequently found on pollinator bodies than native or exotic noninvasive ones, indicating a concerningly higher potential for pollen dispersal and reproduction of the former ones. Intriguingly, pollinator body size mediated the effect of landscape alteration on interactions, as only the largest bees expanded the foraging diet in terms of plant richness in the transported pollen at increasing fragmentation. In parallel, the pollination efficiency increased with pollinator species richness in two sentinel plants. This study shows that moderate landscape fragmentation of green areas shapes many aspects of the pollination ecosystem service, where despite interactions being less complex and mediated by pollinator body size, pollinator insect biodiversity and potential plant reproduction are supported.

Identity and diversity of pollens collected by two managed bee species while in blueberry fields for pollination

The nutritional needs and foraging behavior of managed bees often lead to pollen collection from flowers other than the focal crop during crop pollination. To understand the pollen needs and preferences of managed bees during blueberry pollination, we identified pollen collected by Apis mellifera Linnaeus, 1758 (Hymenoptera: Apidae) and Bombus impatiens Cresson, 1863 (Hymenoptera: Apidae) colonies across two years. Bumble bees collected a wider diversity of pollens compared to honey bees, whereas honey bees were more focused on abundant resources. Despite blueberries being the most abundant resource in the landscape, it was not the most collected pollen by either bee species in 2018. However, it was the most collected pollen by bumble bees in 2019 and they collected substantially more blueberry pollen than honey bees in both years. In 2018, buckthorn, Rhamnus L. (Rosales: Rhamnaceae) or Frangula Mill. (Rosales: Rhamnaceae), and willow, Salix L. (Malpighiales: Salicaceae), pollens were abundantly collected by both bee species. In 2019, cherry, Prunus L. (Rosales: Rosaceae), and willow (Salix) pollens were collected at high proportions by both species. Brambles, Rubus L. (Rosales: Rosaceae), and white clover, Trifolium repens L. (Fabales: Fabaceae), were also common pollen sources for honey bees, whereas oak, Quercus L. (Fagales: Fagaceae), was collected by bumble bees. Landscape analyses also revealed that certain land cover types were positively correlated with the collection of preferred pollen types. Herbaceous wetlands were associated with collection of buckthorn (Rhamnus/Frangula), willow (Salix), and cherry (Prunus) pollen, which were primary pollen resources for both bee species. There was no correlation between landscape diversity and pollen diversity, suggesting that colonies forage based on nutritional requirements rather than resource availability.

Diverse flower-visiting responses among pollinators to multiple weather variables in buckwheat pollination

Response diversity to environmental change among species is important for the maintenance of ecosystem services, but response diversity to changes in multiple environmental parameters is largely unexplored. Here, we examined how insect visitations to buckwheat flowers differ among species groups in response to changes in multiple weather variables and landscape structures. We found differences in responses to changes in weather conditions among insect taxonomic groups visiting buckwheat flowers. Beetles, butterflies, and wasps were more active in sunny and/or high-temperature conditions, whereas ants and non-syrphid flies showed the opposite pattern. When looking closely, the different response pattern among insect groups was itself shown to be different from one weather variable to another. For instance, large insects were responsive to temperatures more than small insects while smaller insects were responsive to sunshine duration more than large insects. Furthermore, responses to weather conditions differed between large and small insects, which agreed with the expectation that optimal temperature for insect activity depends on body size. Responses to spatial variables also differed; large insects were more abundant in fields with surrounding forests and mosaic habitats, whereas small insects were not. We suggest that response diversity at multiple spatial and temporal niche dimensions should be a focus of future studies of the biodiversity-ecosystem service relationships.

The degree of urbanisation reduces wild bee and butterfly diversity and alters the patterns of flower-visitation in urban dry grasslands

Insect-provided pollination services are increasingly threatened due to alarming declines in insect pollinator populations. One of the main threats to insect pollinators and consequently pollination is urbanisation. Here, we investigate the effects of local habitat quality (patch size, flowering plant richness, bare soil cover, vegetation structure), degree of urbanisation (impervious surfaces) and 3D connectivity on bee, hoverfly and butterfly flower visitors and plant-flower visitor networks in flower-rich urban dry grasslands. Overall, the degree of urbanisation and the quality of the local habitat influenced the flowering plant and pollinator communities. Although flowering plant abundance increased with urbanisation, bee species richness and butterfly species richness decreased with increasing impervious surfaces. Flowering plant richness and ground nesting resource availability were positively related to bee richness and local vegetation structure boosted hoverfly and butterfly visitation rates. In terms of plant-pollinator interactions, insect pollinators visited a lower proportion of the available flowering plants in more urbanised areas and network modularity and specialisation increased with patch size. Our findings show that urban dry grasslands are valuable habitats for species-rich pollinator communities and further highlight the importance of minimizing the intensity of urbanisation and the potential of local management practices to support insect biodiversity in cities.

Linear scaling – negative effects of invasive Spiraea tomentosa (Rosaceae) on wetland plants and pollinator communities

Invasive plants directly and indirectly disrupt the ecosystem functioning, of which indirect effects, for example, through trophic cascades, are particularly difficult to predict. It is frequently assumed that the impact of an invading species on the ecosystem is proportional (linearly related) to its density or abundance in a habitat, but this assumption has rarely been tested. We hypothesised that abundance and richness of plants and potentially pollinators of wet meadows change as a result of invasion of steeplebush Spiraea tomentosa and that these changes are proportional to the density of the shrub. We selected 27 sites amongst wet meadows habitats invaded by S. tomentosa with coverage ranging from 0% to 100% and examined the diversity of plants, as well as the abundance and diversity of flower visitors (bees, butterflies with moths and flies). Our results showed that the richness of plants, as well as the richness and number of individuals of flower visitors, decrease significantly and linearly with an increase of the S. tomentosa cover. This finding supports the hypothesis that the impact of an invasive species can be proportional to their population density, especially if this species is limiting the available resources without supplying others. Our study is the first to show such an unequivocal negative, linear effect of an invasive shrub on the abundance and richness of potential pollinators. It proves that the negative impact of S. tomentosa on the wetland ecosystem appears even with a minor coverage of the invader, which should be taken into account when planning activities aimed at controlling the population of this transformer species. The simultaneously detected linear dependence allows us to assume that the benefits of controlling secondary populations of the shrub can be proportional to the incurred effort.

Nesting Biology and Ecology of a Resin Bee, Megachile cephalotes (Megachilidae: Hymenoptera)

We report the nesting biology and ecology of Megachile cephalotes Smith, 1853 for the first time in Pakistan. Wooden and bamboo trap nests were deployed at three different locations in Bahawalpur district, Pakistan, from January 2020 to May 2021. A total of 242 nests of M. cephalotes were occupied in all three locations with the maximum abundance in the Cholistan Institute of Desert Studies. Megachile cephalotes remained active from March to September (the spring and summer seasons). In a nest, females made 7-8 brood cells each having a length of 1.2-2.3 cm. Plant resin was used to construct cells and mud or animal dung to plug the nest entrance. A vestibular cell was also made between the outermost brood cell and the nest entrance that ranged from 1.4 to 2.5 cm in length. No intercalary cells were observed in the nests. The males took 65.3 days to become adults, while the females took 74.78 days. The sex ratio was significantly biased toward females in all three locations. Grewia asiatica was the predominant pollen grain species found in the brood cells. Megachile cephalotes were observed collecting resin from Acacia nilotica, Prosopis juliflora, and Moringa oleifera. Three cleptoparasites of this species were also recorded: Euaspis carbonaria, Coelioxys sp., and Anthrax sp. This study set up a background to encourage new studies on artificial nesting and provides tools for proper biodiversity management and conservation.

Bumble Bee Breeding on Artificial Pollen Substitutes

Bumble bees are important pollinators for many temperate crops. Because of the growing demand for food from entomophilous crops, bumble bee colonies are commercially reared and placed in fields or greenhouses to guarantee sufficient pollination services. Besides, commercial colonies are increasingly used in laboratories for various bioassays under controlled conditions. For both usages, bumble bee colonies are commonly provided with sugar solution and honey bee-collected pollen pellets. However, the latter display several disadvantages since they may contain pollutants, pathogens, or toxic phytochemicals. Consequently, companies have developed pollen-free artificial diets to sustain colonies. Such diets are designed to boost worker health in the field, in complement of floral pollen collected by workers outside the colonies, but their suitability in 'closed' systems without access to floral pollen, such as in laboratory bioassays, is arguable. Here, we used microcolonies of the commercially important bumble bee Bombus terrestris L. (Hymenoptera: Apidae) to assess the suitability of five artificial pollen substitutes and three mixed diets. We also assessed the evaporation rate of the different diets as it could impact their suitability. At the end of the bioassays, microcolonies fed the artificial diets showed a reduced offspring development when compared to microcolonies fed natural pollen, which was partly offset by mixing these diets with natural pollen. By contrast, the artificial diets did not have deleterious effects on worker's health. We discuss the potential nutritional and physical causes of artificial diets unsuitability for offspring development and encourage further research to accordingly establish appropriate pollen-free diets for bumble bee breeding.

California Native Perennials Attract Greater Native Pollinator Abundance and Diversity Than Nonnative, Commercially Available Ornamentals in Southern California

While many factors have been implicated in global pollinator decline, habitat loss is a key driver of wild pollinator decline in both abundance and species richness. An increase in and diversification of pollinator habitat, even in urban settings, can assist in the conservation of pollinator populations. In Southern California, a highly fragmented and urbanized landscape with a rich yet threatened native pollinator fauna, the availability of food resources for native pollinators hinges largely upon the selection of ornamental plants grown in the urban landscape. To examine the pollinator attractiveness of ornamental plants in a Southern California context, we installed an experimental garden with common California native and nonnative ornamental perennials and observed floral visitation and visitor community composition for 3 yr. Our study demonstrates that while native pollinators visited common ornamental perennials native to California at a higher rate than they visited nonnative ornamentals, introduced honey bees showed no significant preference for either native or nonnative species. Native plants also received a greater diversity of visitor taxa, including a richer suite of native bees. Plant species differed dramatically in attractiveness, by as much as a factor of 12, even within the native status group. Our results suggest that including a data-driven selection of both native and non-native ornamental perennials in the urban landscape can diversify the assemblage of native pollinators, provide critical floral resources throughout the year, and reduce the impact of honey bee landscape foraging dominance by providing plants highly attractive to native pollinators and less so to honey bees.

Heat of the moment: extreme heat poses a risk to bee-plant interactions and crop yields

Extreme heat events threaten the development, functioning, and success of bee pollinators and crops that rely on pollinators for high yields. While direct effects of extreme heat and climate warming have gained more attention, the indirect effects on bees and crops remain largely unexplored. Extreme heat can directly alter the nutritional value of floral rewards, which indirectly contributes to lower bee survival, development, and reproduction with implications for pollination. Phenological mismatches between bee activity and crop flowering are also expected. Heat-stressed crop plants with reduced floral rewards may reduce bee foraging and nesting, limiting pollination services. Understanding how extreme heat affects bee-crop interactions will be essential for resilient production of pollinator-dependent crops in this era of climate change.

Effect of Landscape Composition and Invasive Plants on Pollination Networks of Smallholder Orchards in Northeastern Thailand

Destruction of natural habitat, land-use changes and biological invasion are some of the major threats to biodiversity. Both habitat alteration and biological invasions can have impacts on pollinator communities and pollination network structures. This study aims to examine the effect of an invasive plant, praxelis (Praxelis clematidea; Asteraceae), and land-use types on pollinator communities and the structure of pollination networks. We conducted the study in smallholder orchards which are either invaded or non-invaded by P. clematidea. We estimated the pollinator richness, visitation rates, and pollinator diversity and evaluated the network structures from 18 smallholder orchards in Northeastern Thailand. The effect of landscape structure in the vicinity of the orchards was investigated, with the proportion of agricultural, forest, and urban landscape within a 3 km radius analyzed. The invasive species and land-use disturbance influence the pollinator communities and pollination network structure at species level was affected by the presence of P. clematidea. Bees were the most important pollinator group for pollinator communities and pollination networks of both invaded or non-invaded plots, as bees are a generalist species, they provide the coherence of both the network and its own module. The urban landscape had a strong negative influence on pollinator richness, while the proportions of agriculture and forest landscape positively affected the pollinator community.

Powerline Corridors Can Add Ecological Value to Suburban Landscapes When Not Maintained as Lawn

Electric powerline corridors are informal green spaces that encompass large areas of land and have the potential to support biodiversity in urban and suburban landscapes. However, the extent to which these corridors provide novel habitats compared to the surrounding landscape is unclear. Biodiversity in corridors is often compared to that of “natural” habitats despite the fact that the corridors are subject to frequent vegetation management. In urban and suburban landscapes, residential yards may provide a more appropriate comparison because they are a dominant type of green space and are also characterized by frequent vegetation management. We conducted a study of the biodiversity in suburban powerline corridors in northern Illinois, USA, and compared it to the biodiversity found in nearby residential yards. Our goal was to determine whether powerline corridors added ecological value to these suburban landscapes. We included three different management styles of powerline corridors: (1) frequently mowed and kept as lawn, (2) brush mowed on a five-year cycle (“old-field”), and (3) restored and/or maintained as native prairie. We measured the species richness and composition of plants, birds, and insect pollinators in corridors and yards. The corridor management types and comparison yards differed significantly in the richness of all three taxa, with old-field and/or prairie sites having greater species richness than mown corridors and/or comparison yards. Community composition also differed by management category. While the species richness of old-field sites tended to be high, prairie sites generally had more species of conservation interest. Our study shows that both old-field- and prairie-managed powerline corridors add habitat value to Midwestern U.S. suburban landscapes by providing alternative habitat types that support many species. Nonetheless, we suggest that managers looking to specifically support native and/or grassland specialist species in this region should manage sites as prairies when possible.

Pollen-insect interaction meta-networks identify key relationships for conservation in mosaic agricultural landscapes

Flower visitors use different parts of the landscape through the plants they visit, however these connections vary within and among land uses. Identifying which flower-visiting insects are carrying pollen, and from where in the landscape, can elucidate key pollen-insect interactions and identify the most important sites for maintaining community-level interactions across land uses. We developed a bipartite meta-network, linking pollen-insect interactions with the sites they occur in. We used this to identify which land-use types at the site- and landscape-scale (within 500 m of a site) are most important for conserving pollen-insect interactions. We compared pollen-insect interactions across four different land uses (remnant native forest, avocado orchard, dairy farm, rotational potato crop) within a mosaic agricultural landscape. We sampled insects using flight intercept traps, identified pollen carried on their bodies and quantified distinct pollen-insect interactions that were highly specialized to both natural and modified land uses. We found that sites in crops and dairy farms had higher richness of pollen-insect interactions and higher interaction strength than small forest patches and orchards. Further, many interactions involved pollinator groups such as flies, wasps, and beetles that are often under-represented in pollen-insect network studies, but were often connector species in our networks. These insect groups require greater attention to enable wholistic pollinator community conservation. Pollen samples were dominated by grass (Poaceae) pollen, indicating anemophilous plant species may provide important food resources for pollinators, particularly in modified land uses. Field-scale land use (within 100 m of a site) better predicted pollen-insect interaction richness, uniqueness, and strength than landscape-scale. Thus, management focused at smaller scales may provide more tractable outcomes for conserving or restoring pollen-insect interactions in modified landscapes. For instance, actions aimed at linking high-richness sites with those containing unique (i.e., rare) interactions by enhancing floral corridors along field boundaries and between different land uses may best aid interaction diversity and connectance. The ability to map interactions across sites using a meta-network approach is practical and can inform land-use planning, whereby conservation efforts can be targeted toward areas that host key interactions between plant and pollinator species.

Interactive effects of climate and land use on pollinator diversity differ among taxa and scales

Changes in climate and land use are major threats to pollinating insects, an essential functional group. Here, we unravel the largely unknown interactive effects of both threats on seven pollinator taxa using a multiscale space-for-time approach across large climate and land-use gradients in a temperate region. Pollinator community composition, regional gamma diversity, and community dissimilarity (beta diversity) of pollinator taxa were shaped by climate-land-use interactions, while local alpha diversity was solely explained by their additive effects. Pollinator diversity increased with reduced land-use intensity (forest < grassland < arable land < urban) and high flowering-plant diversity at different spatial scales, and higher temperatures homogenized pollinator communities across regions. Our study reveals declines in pollinator diversity with land-use intensity at multiple spatial scales and regional community homogenization in warmer and drier climates. Management options at several scales are highlighted to mitigate impacts of climate change on pollinators and their ecosystem services.

Who can pass the urban filter? A multi-taxon approach to disentangle pollinator trait-environmental relationships

Cities are considered important refuges for insect pollinators. This has been shown repeatedly for wild bees, but may also be true for other diverse taxa such as hoverflies. However, our understanding of how urban environmental filters shape pollinator species communities and their traits is still limited. Here, we used wild bee and hoverfly species, communities and their functional traits to illustrate how environmental filters on the landscape and local scale shape urban species pools. The multi-taxon approach revealed that environmental filtering predominantly occurred at the landscape scale as urbanisation and 3D connectivity significantly structured the taxonomic and functional composition of wild bee (sociality, nesting, diet, body size) and hoverfly (larval food type, migratory status) communities. We identified urban winners and losers attributed to taxon-specific responses to urban filters. Our results suggest that insect pollinator conservation needs to take place primarily at the landscape level while considering species traits, especially by increasing habitat connectivity.

Insect Visitors of Black Cherry (Prunus serotina) (Rosales: Rosaceae) and Factors Affecting Viable Seed Production

Since 2000, wild black cherry (Prunus serotina Ehrh.) has produced erratic seed crops, especially in the Allegheny National Forest where poor seed production has been implicated in difficulties with black cherry regeneration in forest stands. Given that black cherry is insect pollinated and unable to produce viable seed from self-pollination, a reduction in seed crops could be due to a pollination deficit; however, its key pollinators are unknown. Identifying the pollinators and factors that influence pollinator abundance and fidelity is critical for supporting and enhancing seed production for this valuable timber species. Over a two-year period in developed, semideveloped, and forested areas in Pennsylvania, we identified the potential pollinators of black cherry and examined how their abundance, along with several other abiotic and biotic factors, influenced viable seed production. We found that andrenid (Andrenidae: Hymenoptera) bees are likely the most important pollinators. The proportion of viable seeds increased as the number of andrenids increased, and these ground nesting bees were most abundant on forest edges, highlighting this habitat's potential to support pollination services. Andrenids carried an average of 347-fold more black cherry pollen than flies and 18-fold more than halictid (Halictidae: Hymenoptera) bees. We did not find a significant relationship between the abundance of any other taxa besides andrenids and viable seed production. Black cherry flowers also provide resources for natural enemies such as the economically important parasitoid of Popillia japonica Newman (Scarabaeidae: Coleoptera), Tiphia vernalis Rohwer (Tiphiidae: Hymenoptera), which was observed feeding on black cherry nectar in this study.

A review of the opportunities to support pollinator populations in South African cities

Globally insects are declining, but some guilds of pollinators are finding refuge in urban landscapes. The body of knowledge on urban pollinators is relatively mature, which means it is now possible to begin to make generalization. Unfortunately, studies do not represent climatic regions evenly and there is a gap in research from the African continent. This study aimed to address some of the gaps on urban pollination knowledge in South Africa and to identify opportunities to improve urban habitats for pollinators. We reviewed the international literature on urban pollinators and the South African literature on pollinators with a landscape ecology focus, drawing on literature with an emphasis on agricultural and ecosystem services. The findings show that some taxa (e.g. large-bodied, cavity nesting bees) will exploit urban environments increasing in abundance with urban intensity. Moderately sensitive taxa (such as small-bodied, ground-nesting bees) take advantage of urban environments only if local habitats are supportive of their needs for resource provision and habitat connectivity. The South African urban poor rely on pollination services for subsistence agriculture and the reproduction of wild-foraged medicines and food. Potential interventions to improve habitat quality include strategic mowing practices, conversion of turf-grass to floral rich habitats, scientific confirmation of lists of highly attractive flowers, and inclusion of small-scale flower patches throughout the urban matrix. Further research is needed to fill the Africa gap for both specialized and generalized pollinators (Diptera, Halictids, Lepidoptera and Hopliini) in urban areas where ornamental and indigenous flowering plants are valued.

Community structure of pollinating insects and its driving factors in different habitats of Shivapuri‐Nagarjun National Park, Nepal

Insect pollinators are important means for a stable ecosystem. The habitat types play a crucial role in the community composition, abundance, diversity, and species richness of the pollinators. The present study in Shivapuri‐Nagarjun National Park explored the species richness and abundances of insect pollinators in four different habitats and different environmental variables in determining the community composition of the pollinators. Data were collected from 1,500 m to 2,700 m using color pan traps and hand sweeping methods. Non‐Metric Multidimensional Scaling (NMDS) and Redundancy Analysis (RDA) were conducted to show the association between insect pollinators and environmental variables. The results firmly demonstrated that species richness and abundances were higher (158) in Open trail compared to other habitats. The distribution of the pollinator species was more uniform in the Open trail followed by the Grassland. Similarly, a strong positive correlation between flower resources and pollinators' abundance (R² = .63, P < .001) was found. In conclusion, the Open trail harbors rich insect pollinators in lower elevation. The community structure of the pollinators was strongly influenced by the presence of flowers in the trails.

A global-scale expert assessment of drivers and risks associated with pollinator decline

Pollinator decline has attracted global attention and substantial efforts are underway to respond through national pollinator strategies and action plans. These policy responses require clarity on what is driving pollinator decline and what risks it generates for society in different parts of the world. Using a formal expert elicitation process, we evaluated the relative regional and global importance of eight drivers of pollinator decline and ten consequent risks to human well-being. Our results indicate that global policy responses should focus on reducing pressure from changes in land cover and configuration, land management and pesticides, as these were considered very important drivers in most regions. We quantify how the importance of drivers and risks from pollinator decline, differ among regions. For example, losing access to managed pollinators was considered a serious risk only for people in North America, whereas yield instability in pollinator-dependent crops was classed as a serious or high risk in four regions but only a moderate risk in Europe and North America. Overall, perceived risks were substantially higher in the Global South. Despite extensive research on pollinator decline, our analysis reveals considerable scientific uncertainty about what this means for human society.

Landscape Effects on Native Bees (Hymenoptera: Anthophila) Captured in Pheromone Traps for Noctuid Crop Pests (Lepidoptera: Noctuidae)

Noctuid pests, including tobacco budworm (Chloridea virescens (Fab.)) and bollworm (Helicoverpa zea (Boddie)), are significant pests of southern row crops including cotton (Gossypium hirsutum L.), corn (Zea mays L.), and soybean (Glycine max (L.) Moench.). This pest complex is seasonally monitored through Hartstack traps that are baited with synthetic lepidopteran pheromones across the southern United States. We examined bycatch from the noctuid traps deployed across the Mississippi Delta in 2015, 2016, and 2017 for the presence of bees. The most abundant species collected were honey bees (Apis mellifera L.), bumble bees (Bombus spp.), and long-horned bees (Melissodes spp.); these three genera accounted for 82.4% of specimens collected. We also evaluated the proportion of local- and landscape-level habitats on the abundance and richness of the bees caught as bycatch. The proportion of natural and semi-natural habitat affected the abundance and richness of bees collected at the landscape level, but not at more local scales. Additional research is needed to better understand these interactions between bycatch and landscape factors to minimize non-target collections.

Japanese Honeybees (Apis cerana japonica Radoszkowski, 1877) May Be Resilient to Land Use Change

Simple Summary

Pollinators are threatened globally by growing urban sprawl and agriculture. The Western Honeybee (Apis mellifera) readily adapts to whatever food is available, so people have made it the most widely distributed pollinator across the world. Previous research has suggested that the Western Honeybee may be less resilient to land use change outside of its natural range. This study examines a different honeybee species—the Japanese Honeybee (Apis cerana japonica). Unlike the Western Honeybee, this species is found almost exclusively in its natural range in Japan. Consequently, it may be better adapted to its local food sources and therefore more resilient. Working in southern Japan, in the Nagasaki and Saga prefectures, we looked at the nectar and pollen that the Japanese Honeybee feeds on. Their food intake was then examined in relation to local land use composition. We found minimal impact of increasing urban sprawl on the forage of the Japanese Honeybee. This goes against previous studies on the Western Honeybee elsewhere in the world. Though in need of a direct comparison with Western Honeybee, these preliminary results could be due to differences in urban green infrastructure in Japan, or due to an adaptation by the Japanese honeybee to its surroundings.

Abstract

Pollinators are being threatened globally by urbanisation and agricultural intensification, driven by a growing human population. Understanding these impacts on landscapes and pollinators is critical to ensuring a robust pollination system. Remote sensing data on land use attributes have previously linked honeybee nutrition to land use in the Western Honeybee (Apis mellifera L.). Here, we instead focus on the less commonly studied Apis cerana japonica—the Japanese Honeybee. Our study presents preliminary data comparing forage (honey and pollen) with land use across a rural-urban gradient from 22 sites in Kyushu, southern Japan. Honey samples were collected from hives between June 2018 and August 2019. Pollen were collected and biotyped from hives in urban and rural locations (n = 4). Previous studies of honey show substantial variation in monosaccharide content. Our analysis of A. cerana japonica honey found very little variation in glucose and fructose (which accounted for 97% of monosaccharides), despite substantial differences in surrounding forage composition. As expected, we observed temporal variation in pollen foraged by A. cerana japonica, likely dependent on flowering phenology. These preliminary results suggest that the forage and nutrition of A. cerana japonica may not be negatively affected by urban land use. This highlights the need for further comparative studies between A. cerana japonica and A. mellifera as it could suggest a resilience in pollinators foraging in their native range.

Using Matching Traits to Study the Impacts of Land-Use Intensification on Plant-Pollinator Interactions in European Grasslands: A Review

Simple Summary

Permanent grasslands are main habitats for many plant species and pollinators. Their destruction as well as their intensification has a major impact on plant and pollinator biodiversity, which has a cascading effect on pollination. However, we lack an understanding of these effects, thereby limiting our ability to predict them. In this review, we synthesised the literature on the mechanisms behind this cascade to provide new insights into the relationship between land-use intensification and pollination. By matching functional traits that mediate the relationship between the two trophic levels, we identified major knowledge gaps about how land-use intensification affects plant–pollinator interactions and how it favours plants with generalised floral traits, which are likely harmful to pollination.

Abstract

Permanent grasslands are suitable habitats for many plant and animal species, among which are pollinating insects that provide a wide range of ecosystem services. A global crisis in pollination ecosystem service has been highlighted in recent decades, partly the result of land-use intensification. At the grassland scale, however, the underlying mechanisms of land-use intensification that affect plant–pollinator interactions and pollination remain understudied. In this review, we first synthesise the literature to provide new insights into the relationships between land-use intensification and pollination by using matching community and interaction traits. We then identify knowledge gaps and summarise how land-use intensification of grassland influences floral traits that may in turn be associated with modifications to pollinator matching traits. Last, we summarise how these modifications may affect pollination function on permanent grasslands. Overall, land-use intensification may lead to a shift in flower colour, a decrease in mean nectar tube depth and a decrease in reward production and pollen quality at the community level. This, in turn, may generate a decrease in pollinator mouthparts length and body size, that may favour pollinators that require a low amount of floral reward. We found no study citing the effect of land-use intensification on volatile organic compounds emitted by flowers despite the importance of these molecules in pollinator community composition. Overall, our review highlighted major knowledge gaps about the effects of land-use intensification on plant–pollinator interactions, and suggests that land-use intensification could favour plants with generalised floral traits that adversely affect pollination.

Designing a survey to monitor multi-scale impacts of agri-environment schemes on mobile taxa

Agri-environment schemes (AES) are key mechanisms to deliver conservation policy, and include management to provide resources for target taxa. Mobile species may move to areas where resources are increased, without this necessarily having an effect across the wider countryside or on populations over time. Most assessments of AES efficacy have been at small spatial scales, over short timescales, and shown varying results. We developed a survey design based on orthogonal gradients of AES management at local and landscape scales, which will enable the response of several taxa to be monitored. An evidence review of management effects on butterflies, birds and pollinating insects provided data to score AES options. Predicted gradients were calculated using AES uptake, weighted by the evidence scores. Predicted AES gradients for each taxon correlated strongly, and with the average gradient across taxa, supporting the co-location of surveys across different taxa. Nine 1 × 1 km survey squares were selected in each of four regional blocks with broadly homogenous background habitat characteristics. Squares in each block covered orthogonal contrasts across the range of AES gradients at local and landscape scales. This allows the effects of AES on species at each scale, and the interaction between scales, to be tested. AES options and broad habitats were mapped in field surveys, to verify predicted gradients which were based on AES option uptake data. The verified AES gradient had a strong positive relationship with the predicted gradient. AES gradients were broadly independent of background habitat within each block, likely allowing AES effects to be distinguished from potential effects of other habitat variables. Surveys of several mobile taxa are ongoing. This design will allow mobile taxa responses to AES to be tested in the surrounding countryside, as well as on land under AES management, and potentially in terms of population change over time. The design developed here provides a novel, pseudo-experimental approach for assessing the response of mobile species to gradients of management at two spatial scales. A similar design process could be applied in other regions that require a standardized approach to monitoring the impacts of management interventions on target taxa at landscape scales, if equivalent spatial data are available.

Effects of Natural Habitat Loss and Edge Effects on Wild Bees and Pollination Services in Remnant Prairies

Habitat loss and edge effects resulting from habitat fragmentation are key processes implicated in the decline of bee populations globally. Their effects on wild bees and their pollination services in natural ecosystems are poorly understood, particularly in North American prairies. Our objectives were to determine whether natural habitat loss and edge effects affect bee abundance and pollination services in the Northern Great Plains. We sampled bee abundance and pollination services along transects beginning at road or tree edges in grasslands located in Manitoba, Canada. We measured bee abundance using pan traps, and pollination services using seed-set of Brassica rapa (L.) (Brassicales: Brassicaceae) phytometers. We collected local-scale habitat data by measuring occurrence of flowering species, vegetation type, and vegetation structure, and we measured habitat amount at 1-km radii using GIS analysis of landscape cover. Increasing amounts of habitat loss resulted in declines in bee abundance, and sometimes in pollination services. Results varied with bee life-history: proximity to road edges negatively affected social bees, and litter depth had negative effects on below- ground-nesting bees. Surprisingly, few effects on bees led to corresponding impacts on pollination services. This suggests that conservation of intact natural habitat across the northern Great Plains is important for maintaining resilient and diverse bee communities, but that efforts to conserve bee populations cannot be assumed to also maintain all associated pollination services.

Agroecological Strategies to Safeguard Insect Pollinators in Biodiversity Hotspots: Chile as a Case Study

Industrial agriculture (IA) has been recognized among the main drivers of biodiversity loss, climate change, and native pollinator decline. Here we summarize the known negative effects of IA on pollinator biodiversity and illustrate these problems by considering the case of Chile, a “world biodiversity hotspot” (WBH) where food exports account for a considerable share of the economy in this country. Most of Chile’s WBH area is currently being replaced by IA at a fast pace, threatening local biodiversity. We present an agroecological strategy for sustainable food production and pollinator conservation in food-producing WBHs. In this we recognize native pollinators as internal inputs that cannot be replaced by IA technological packages and support the development of agroecological and biodiversity restorative practices to protect biodiversity. We suggest four fundamental pillars for food production change based on: (1) sharing the land, restoring and protecting; (2) ecological intensification; (3) localized knowledge, research, and technological development; and (4) territorial planning and implementation of socio-agroecological policies. This approach does not need modification of native pollination services that sustain the world with food and basic subsistence goods, but a paradigm change where the interdependency of nature and human wellbeing must be recognized for ensuring the world’s food security and sovereignty.

Landscape and Local Drivers Affecting Flying Insects along Fennel Crops (Foeniculum vulgare, Apiaceae) and Implications for Its Yield

Agricultural landscapes are increasingly characterized by intensification and habitat losses. Landscape composition and configuration are known to mediate insect abundance and richness. In the context of global insect decline, and despite 75% of crops being dependent on insects, there is still a gap of knowledge about the link between pollinators and aromatic crops. Fennel (Foeniculum vulgare) is an aromatic plant cultivated in the South of France for its essential oil, which is of great economic interest. Using pan-traps, we investigated the influence of the surrounding habitats at landscape scale (semi-natural habitat proportion and vicinity, landscape configuration) and local scale agricultural practices (insecticides and patch size) on fennel-flower-visitor abundance and richness, and their subsequent impact on fennel essential oil yield. We found that fennel may to be a generalist plant species. We did not find any effect of intense local management practices on insect abundance and richness. Landscape configuration and proximity to semi-natural habitat were the main drivers of flying insect family richness. This richness positively influenced fennel essential oil yield. Maintaining a complex configuration of patches at the landscape scale is important to sustain insect diversity and crop yield.

Rich and abundant spider communities result from enhanced web capture breadth and reduced overlap in urban greenspaces

Urbanization is a key contributor to biodiversity loss, but evidence is mounting that cities can support rich arthropod communities, including rare and threatened species. Furthermore, greenspace is growing within hundreds of "shrinking cities" that have lost population resulting in a need to demolish an overabundance of infrastructure creating vacant land. Efforts are underway to transform vacant lots, often viewed as blighted areas, into habitats that promote biodiversity and generate ecosystem services, such as urban agroecosystems. To understand how reconfiguring these greenspaces might influence species conservation, elucidation of the factors that drive the distribution of an urban species pool is needed. In particular, the importance of species interactions in structuring urban communities is poorly understood. We tested hypotheses that (1) greater breadth of prey captured by web-building spiders and reduced overlap of prey capture among individuals facilitates the conservation of genera richness and abundance and (2) heterogeneity within a greenspace patch facilitates enhanced dietary niche breadth and greater resource partitioning. In 2013 and 2014, the abundance, breadth and degree of overlap in prey capture of sheet web spiders (Linyphiidae) was measured using web mimic traps at 160 microsites (0.25 m² ) situated in four urban vacant lots and four urban farms in the city of Cleveland, Ohio, USA. Within a subset of 40 microsites, we used vacuum sampling and hand collection to measure the abundance and genera richness of Linyphiidae. Spider richness and abundance were significantly reduced within urban farms relative to vacant lots. The distribution of spiders and prey was explained by habitat structure, with microsites dominated by tall grasses and flowering plants, with a high bloom abundance and richness, supporting greater prey capture and a higher genera richness and abundance of spiders. In 2014, web capture overlap was significantly greater within microsites dominated by bare ground. These findings illustrate that urban greenspace conservation efforts that focus on reducing bare ground and incorporating a diversity of grasses and flowering plant species can promote linyphiid spiders, potentially by relaxing exploitative competition for shared prey.

Supporting Bees in Cities: How Bees Are Influenced by Local and Landscape Features

Simple Summary

Cities are complex ecosystems that, while generally contributing to an overall reduction in biodiversity, can support surprisingly unique communities of organisms including bees. Bees are both ecologically and economically essential, therefore preserving and conserving these insects represents a significant challenge as cities continue to expand and diminish surrounding landscapes. Some attempts to support bees in cities have included establishing and improving urban green spaces. Exactly how bees and, to a lesser extent, other pollinators respond to these green spaces in addition to other urban landscape and local features, however, remains incompletely understood. Therefore, this review summarizes the current literature and generalizable trends in pollinator response to urban landscape and local features. While some functional traits or characteristics of bees such as dietary breadth and nesting strategy are more conclusively understood and supported, other characteristics such as sociality remain less generalizable. Lack of knowledge on bee responses to city features is in part due to the individual variation exhibited across different groups and species. To promote greater biodiversity in urban spaces, research should focus on specific responses to urban local and landscape features and how green spaces can be optimized for sustainable bee conservation.

Abstract

Urbanization is a major anthropogenic driver of decline for ecologically and economically important taxa including bees. Despite their generally negative impact on pollinators, cities can display a surprising degree of biodiversity compared to other landscapes. The pollinating communities found within these environments, however, tend to be filtered by interacting local and landscape features that comprise the urban matrix. Landscape and local features exert variable influence on pollinators within and across taxa, which ultimately affects community composition in such a way that contributes to functional trait homogenization and reduced phylogenetic diversity. Although previous results are not easily generalizable, bees and pollinators displaying functional trait characteristics such as polylectic diet, cavity-nesting behavior, and later emergence appear most abundant across different examined cities. To preserve particularly vulnerable species, most notably specialists that have become underrepresented within city communities, green spaces like parks and urban gardens have been examined as potential refuges. Such spaces are scattered across the urban matrix and vary in pollinator resource availability. Therefore, ensuring such spaces are optimized for pollinators is imperative. This review examines how urban features affect pollinators in addition to ways these green spaces can be manipulated to promote greater pollinator abundance and diversity.

Type and intensity of surrounding human land use, not local environment, shape genetic structure of a native grassland plant

Landscape heterogeneity can shape genetic structure and functional connectivity of populations. When this heterogeneity imposes variable costs of moving across the landscape, populations can be structured according to a pattern of "isolation by resistance" (IBR). At the same time, divergent local environmental filters can limit gene flow, creating an alternative pattern of "isolation by environment" (IBE). Here, we evaluate IBR and IBE in the insect-pollinated, biennial plant Sabatia angularis (L.) Pursh (Gentianaceae) across serpentine grasslands in the fragmented landscape of SE Pennsylvania, USA using ~4500 neutral SNP loci. Specifically, we test the extent to which radical alteration of the landscape matrix by humans has fundamentally altered the cost of movement, imprinting a pattern of IBR dictated by land use type and intensity, and the potential for IBE in relation to a gradient of heavy metal concentrations found in serpentine soil. We reveal a strong signal of IBR and a weak signal of IBE across sites, indicating the greater importance of the landscape matrix in shaping genetic structure of S. angularis populations in the study region. Based on Circuitscape and least cost path approaches, we find that both low- and high-intensity urbanization resist gene flow by orders of magnitude greater than "natural" habitats, although resistance to low-intensity urbanization weakens at larger spatial scales. While cropland presents a substantially lower barrier than urban development, cumulative human land use surrounding populations predicts within-population genetic diversity and inbreeding in S. angularis. Our results emphasize the role of forest buffers and corridors in facilitating gene flow between serpentine grassland patches and averting local extinction of plant populations.

Landscape-Based Visions as Powerful Boundary Objects in Spatial Planning: Lessons from Three Dutch Projects

In a context of a rapidly changing livability of towns and countryside, climate change and biodiversity decrease, this paper introduces a landscape-based planning approach to regional spatial policy challenges allowing a regime shift towards a future land system resilient to external pressures. The concept of nature-based solutions and transition theory are combined in this approach, in which co-created normative future visions serve as boundary concepts. Rather than as an object in itself, the landscape is considered as a comprehensive principle, to which all spatial processes are inherently related. We illustrate this approach with three projects in the Netherlands in which landscape-based visions were used to guide the land transition, going beyond the traditional nature-based solutions. The projects studied show that a shared long-term future landscape vision is a powerful boundary concept and a crucial source of inspiration for a coherent design approach to solve today’s spatial planning problems. Further, they show that cherishing abiotic differences in the landscape enhances sustainable and resilient landscapes, that co-creation in the social network is a prerequisite for shared solutions, and that a landscape-based approach enhances future-proof land-use transitions to adaptive, circular, and biodiverse landscapes.

Exploitative competition and displacement mediated by eusocial bees: experimental evidence in a wild pollinator community

Abstract

Eusocial bees are likely to be ecologically important competitors for floral resources, although competitive effects can be difficult to quantify in wild pollinator communities. To investigate this, we excluded honeybees (HBE treatment), bumblebees (BBE) or both (HB&BBE) from wild-growing patches of bramble, Rubus fruticosus L. agg., flowers in two eight-day field trials at separate locations, with complementary mapping of per-site local floral resource availability. Exclusions increased per-flower volume of nectar and visitation rates of non-excluded bees, compared to control patches with no bee exclusions (CON). There was a large increase in average nectar standing crop volume both at Site 1 (+ 172%) and Site 2 (+ 137%) in HB&BBE patch flowers, and no significant change in HBE or BBE, compared to CON patches. Foraging bee responses to exclusion treatments were more pronounced at Site 2, which may be due to lower local floral resource availability, since this is likely to increase the degree of exploitative competition present. Notably, at Site 2, there was a 447% increase in larger-bodied solitary (non-Apis/Bombus) bees visiting HB&BBE patches, suggesting ecological release from competition. Hoverflies showed no response to bee removals. Numbers of other non-bee insect groups were very small and also showed no clear response to exclusions. Our findings reveal patterns of competitive exclusion between pollinator groups, mediated by resource depletion by eusocial bees. Possible long-term implications of displacement from preferred flowers, particularly where alternative forage is reduced, are discussed.

Significance statement

Understanding patterns of exploitative competition and displacement is necessary for pollinator conservation, particularly for vulnerable or threatened species. In this research, experimental methods reveal underlying patterns of resource competition exerted by eusocial bees in a wild pollinator community. We show that honeybees and bumblebees competitively displace each other and particularly solitary (non-Apis/Bombus) bees from bramble, an important native nectar and pollen source. Effects were stronger where local floral resource availability was identified to be limited. Notably, following experimental exclusion of both honey- and bumblebees from flowers, visitation by solitary bees increased by up to 447%, strongly suggesting ecological release from competition. These results highlight the need for informed landscape management for pollinator wellbeing, including appropriate honeybee stocking densities and improved floral resource availability.