Bee Abundance Research Articles

Bee diversity decreases rapidly with time since harvest in intensively managed conifer forests.

Despite widespread concerns about the anthropogenic drivers of global pollinator declines, little information is available about the impacts of land management practices on wild bees outside of agricultural systems, including in forests managed intensively for wood production. We assessed changes in wild bee communities with time since harvest in 60 intensively managed Douglas-fir (Pseudotsuga menziesii) stands across a gradient in stand ages spanning a typical harvest rotation. We measured bee abundance, species richness, and alpha and beta diversity, as well as habitat characteristics (i.e., floral resources, nesting substrates, understory vegetation, and early seral forest in the surrounding landscape) during the spring and summer of 2018 and 2019. We found that bee abundance and species richness declined rapidly with stand age, decreasing by 61% and 48%, respectively, for every 5 years since timber harvest. Asymptotic estimates of Shannon and Simpson diversity were highest in stands 6-10 years post-harvest and lowest after the forest canopy had closed, ~11 years post-harvest. Bee communities in older stands were nested subsets of bee communities found in younger stands, indicating that changes were due to species loss rather than turnover as the stands aged. Bee abundance-but not species richness-was positively associated with floral resource density, and neither metric was associated with floral richness. The amount of early seral forest in the surrounding landscape seemed to enhance bee species richness in older, closed-canopy stands, but otherwise had little effect. Changes in the relative abundance of bee species did not relate to bee functional characteristics such as sociality, diet breadth, or nesting substrate. Our study demonstrates that Douglas-fir plantations develop diverse communities of wild bees shortly after harvest, but those communities erode rapidly over time as forest canopies close. Therefore, stand-scale management activities that prolong the precanopy closure period and enhance floral resources during the initial stage of stand regeneration will provide the greatest opportunity to enhance bee diversity in landscapes dominated by intensively managed conifer forests.

Agricultural land-use and landscape composition: Response of wild bee species in relation to their characteristic traits

In the past centuries, farmland has undergone a fundamental transformation through changed farming practices, such as the use of agrochemicals and advanced machine processing. Particularly since the 1970s, agriculturally driven land-use change has caused destruction of natural and semi-natural habitats, and as a consequence, severe loss of biodiversity. Hence, identifying landscape patterns and habitats that enhance species richness, and detecting species and traits that are most vulnerable to intensive land-use are prerequisites for conservation. To evaluate the effects of agricultural land-use and landscape composition on wild bees, we investigated 340 cross-transects in 34 test areas in the main agricultural regions of Austria within the framework of the biodiversity monitoring program BINATS. Using multivariate models (GLM, DCA), wild bees and potential explanatory parameters (e.g. Shannon landscape diversity index, plant diversity, flower cover) were documented, and their interrelationships analyzed. We found strong negative effects of increased agricultural land cover on species richness, abundance and functional richness. Species richness was positively correlated with an increasing area of semi-natural elements (e.g. extensive grassland, hedgerows, fallows) and the number of different habitat types, while wild bee abundance was best explained by the presence of semi-natural habitats and flower cover. Colletidae were significantly associated with the area of semi-natural elements, and were especially sensitive to agricultural intensification. Many species from communities that are present in complex landscapes disappeared in intensively managed farmland, and the majority of species decreased in response to simplified landscapes. A few species, however, even benefited. Our results emphasize the importance of diverse semi-natural elements and high regional flower cover within farmland for maintaining and enhancing species richness and abundance, and for promoting a positive spillover effect of pollinators to the surrounding agricultural landscape. Especially members of the family Colletidae, with a high proportion of specialized species, will benefit from diverse semi-natural habitat types. Given the unique importance of wild bees as pollinators of wildflowers and crops, it is crucial to improve and expand agri-environmental schemes to combat ongoing biodiversity loss in farmland.

B.Y.O. Bees: Managing wild bee biodiversity in urban greenspaces.

As cities become more populated and the density of urban development increases, local biodiversity is threatened. Urban greenspaces have the capacity to preserve pollinator biodiversity, but the quality of support they provide depends on greenspace landscape attributes, including the availability of pollinator habitat and foraging resources. Wild native bees provide important pollination services to urban ecosystems, yet relatively little is known about how urban landscape management influences pollinator community composition and diversity. Our study explores how wild bee communities are affected by greenspace and landscape-level features like pollinator management practices, in urban greenspaces in and around Appleton Wisconsin: a mid-sized urban community spanning more than 100 sq. km. We sampled and identified native bees periodically between late-May 2017 and mid-September of 2018 using standardized arrays of pan traps at 15 sites around the city. We classified greenspaces based on their level of development (urban or suburban) and whether they were managed or unmanaged for increasing wild pollinator diversity. We quantified floral species diversity, floral color diversity, tree species diversity, and proximity of sites to open water for each site and used remotely sensed satellite data from both the USGS National Land Cover Database (NLCD) and the Normalized Difference Vegetation Index (NDVI). All variables were tested as potential correlates of wild bee abundance and species richness. Active pollinator management sites supported higher levels of bee abundance and richness. Notably, active greenspace management (e.g. planting native wildflowers) was a stronger correlate of bee abundance and richness than greenspace size and other landscape-level attributes. Within-greenspace attributes such as floral diversity, tree diversity, and proximity to open water contributed positively to both bee abundance and richness. Based on these findings, we suggest that urban greenspaces may be managed more efficiently and cost-effectively by focusing resources on active management by planting wildflowers, removing invasive species, creating nesting habitat, and providing water resources, rather than simply expanding in area.

The effect of urbanisation and seasonality on wild bee abundance, body size and foraging efforts

Abstract Anthropogenic changes highly impact the world's biodiversity. An important human‐driven change to natural environments is increasing urbanisation, which is responsible for decreasing suitable habitats for many wild species, including bees. In this study, we investigate if three levels of urbanisation (low, medium and high) affect body size, foraging efforts and abundance of the sweat bee Agapostemon virescens. Overall, A. virescens was more abundant in medium‐urbanised sites. Second‐generation females (summer bees) were more abundant than overwintered (spring bees) at all levels of urbanisation. According to body size, female bees were larger in highly urbanised sites and male bees were larger in medium‐urbanised sites. According to foraging efforts, we observed an increase in wing wear during spring and a decrease during summer. It was also found a female‐biased sex ratio under high urbanisation and a male‐biased in low urbanisation sites. Our results suggest that highly urbanised sites can still provide sufficient nesting and foraging resources for A. virescens. In addition to our findings of higher bee abundance in low and medium urbanised sites, we suggest that maintaining different levels of urbanisation and heterogenous landscapes within a populous city might have a more positive impact on wild be sustainability.

Native and introduced pollinators vary in their seasonal floral resource visitation and selection between native and exotic plant species

Abstract Anthropogenic pressures on native ecosystems have resulted in numerous functional and compositional changes, creating novel ecosystems with new interactions between native and exotic species. How native species utilize these resources is crucial for their management in altered landscapes and the promotion of their essential ecosystem services. We compared seasonal floral selection between European honey bees and their most phylogenetically similar native component in our study region, bumble bees, in North American grasslands with high densities of exotic plant species. Additionally, we determined whether floral species richness, total flowering density, native floral density or exotic floral density best explained the abundance of both groups. Selection analyses revealed that honey bees and native bumble bees differed in selection between native and non‐native floral resource availability, with any significant selection of honey bees being for exotic plants while native bumble bees selected for native plants. Native forb presence and floral richness best explained the variation in bumble bee abundance, while honey bee abundance was associated with flowering densities in the early and mid‐seasons and floral richness in both the early and late seasons. Despite their generalist diets, we emphasize the importance of native floral availability for bumble bee foraging in novel grassland landscapes and the importance of exotic plants to support honey bee production. Synthesis and applications. Our results indicate that pollinator forage management should differ for non‐native and native species, despite morphological and life‐history similarities. However, greater floral diversity provides a common management focus that can benefit honey bees and bumble bees in particular seasonal periods. Our results suggest that management actions promoting resource diversity can benefit functionally different species. In grasslands, implementing disturbance processes that can favour floral expression (e.g. fire; grazing) can support bumble bees of conservation concern and agriculturally important bees simultaneously.

Composition and Nutrition of Wild Bees in Solanum melongena L. Agroecosystems in Pune, Maharashtra, India

Eggplant, (Solanum melongena L.), also called aubergine or Guinea squash, in the nightshade family (Solanaceae) is an economically important crop in India. We investigated the significance of Solanum melongena pollen in the diet of wild bees found in agroecosystems by examining pollen on the bees using a pollen load analysis and a nutritive analysis. We selected five agricultural sites that cultivate S. melongena near Pune, Maharashtra, India. At each site, over a two-year period, we sampled the wild bees that visited mature flowers. We sampled pollen from mature flowers and also from the bodies of the bee specimens. The pollen grains from the bees were observed under a light microscope and a scanning electron microscope. They were counted using a Neubauer chamber and the pollen probability index for each bee species was calculated. The nutritive value of S. melongena pollen was estimated by extracting and characterising their proteins using liquid chromatography mass-spectrometry. Protein peptides sequences were extracted from the NCBI protein database to examine their essential amino acids. We collected 324 bees representing 11 species in three families involved in S. melongena pollination. Apis florea and A. cerana were the most abundant bees that visited S. melongena flowers. Pollen load size is highly variable ranging between few thousand to 134146 pollen grains per bee. However, the pollen probability index indicated a high degree of specificity to S. melongena pollen. S. melongena has high pollen protein content and a total of 10 different proteins were identified that are important for plant cell activities as well as the nourishment of pollinators. Further proteomic characterization of the indicated that nearly half the essential amino acids played and nutrient role in the bees. This study highlights that nutrititive composition of S. melongena pollen and highlights its potential to play a significant role in wild bee diets.

Spillover of chalkbrood fungi to native solitary bee species from non‐native congeners

Abstract Introduced, managed bees such as mason bees (genus Osmia) can confer significant pollination benefits to agricultural systems, but a risk of introducing non‐native species into new ecosystems is the co‐introduction of pathogens along with them. Pathogen spillover to wild, native bees may then drive native bee species declines. This study examined prevalence of the chalkbrood‐causing fungal genus Ascosphaera in the nests of both non‐native and native mason bee species. We conducted large‐scale trap‐nesting and pan‐trapping efforts across the Mid‐Atlantic United States with community scientists. Using molecular methods, nests were screened for all known Ascosphaera species in which genetic sequences have been published. After finding Ascosphaera species first described in Asia, we compared their local prevalence with the local abundance of mason bees from Asia. Lastly, we compared the prevalence of co‐introduced Ascosphaera species across sites with a variety of landcover profiles. Results indicate species originally described in Japan, Ascosphaera naganensis and Ascosphaera fusiformis, are now present in native Virginia mason bees, Osmia lignaria and Osmia georgica, with high prevalence of A. naganensis found in O. georgica. We also found that the declining native mason bee O. georgica experienced higher prevalence of non‐native Ascosphaera spp. at sites with larger numbers of non‐native O. cornifrons and O. taurus, perhaps indicating greater likelihood of spillover of these Ascosphaera species with greater sources of transmission. Lastly, when the proportion of agricultural landcover surrounding bee nests was high, there was greater prevalence of non‐native Ascosphaera in O. georgica compared to more natural landcover types. Synthesis and applications. Through community science programming, we documented species of Japanese chalkbrood fungi inside native mason bee nests in North America. Native mason bees encounter non‐native fungi more frequently with increasing abundance of non‐native mason bees. Agricultural landscapes may exacerbate spillover of non‐native fungi for native mason bees. Any use of non‐native bee species in agriculture should involve monitoring native bees for pathogens in the surrounding area for detection of spillover and species declines.

Tailoring your bee sampling protocol: Comparing three methods reveals the best approaches to capturing bees

Abstract Bees are prolific, vital pollinators in agricultural and natural settings, but some taxa are declining. Surveying bees is crucial to understand the needs of these taxa; however, we lack a fine‐grained understanding of assemblages associated with different sampling methods that would enable us to analyse data range‐wide. Here we examine the difference in abundance and richness of bees (bee bowls and vane traps only) and bumble bees (genus Bombus; bee bowls, blue vane traps and target netting) sampled with these methods from mixed‐grass prairie to alpine habitats in Wyoming, USA. We collected four times more bees and twice as many genera of bees in vane traps than bee bowls. Vane traps captured more individuals of abundant genera than bee bowls. Bombus species abundance did not vary between vane traps and target netting; however, richness was higher in vane traps. Bee bowls captured few Bombus species. Overall, we recommend using vane traps to sample most bees, and a combination of vane traps and target netting to collect bumble bees. We evaluated how three sampling techniques perform when surveying for wild bees, which will aid in identifying declining species as well as monitoring species of conservation concern.

Bee functional traits and their relationship to pollination services depend on many factors: A meta‐regression analysis

Abstract Understanding relationships between organisms and the ecosystem services they provide is crucial for predicting the impacts of continued biodiversity changes. Functional traits of organisms can affect ecosystem properties and are thus increasingly used to predict long‐term ecosystem functioning. Bees are ideal taxa for using functional approaches given their role in pollination for many plant species and wide diversity of traits. Although distributions of bee functional traits are being documented in the literature, there is a clear lack of understanding of how they relate to ecosystem functioning (i.e. pollination). To address this knowledge gap, we conducted a meta‐regression analysis with the following objectives: (1) quantify the effects of bee functional traits on pollination and (2) assess sources of heterogeneity to identify variables that might explain variation across studies. Seventeen studies met our criteria for inclusion, yielding 45 individual effect sizes for six traits (body size, tongue length, diet breadth, nesting, parasitism, and sociality). Overall, bee functional traits had a significant effect on pollination; however, effect sizes were weak with high variability across studies. Sources of heterogeneity included the metrics used to quantify pollination, the number of bee genera analysed in a study, and whether traits were measured categorically or continuously. These results indicate a need for more research to improve understanding of trait–pollination relationships. For some bee traits, effects on pollination may be dependent on other factors like bee abundance, environmental context, and the plant species evaluated in studies.

A novel approach for surveying flowers as a proxy for bee pollinators using drone images

The abundance and diversity of plants and insects are important indicators of biodiversity, overall ecosystem health and agricultural production. Bees in particular are interesting indicators as they provide a key ecosystem service in many agricultural crops. Worldwide, habitat loss and fragmentation, agricultural intensification and climate change are important drivers of plant and bee decline. Monitoring of plants and bees is a crucial first step to safeguard their diversity and the services they provide but traditional in situ methods are time consuming and expensive. Remote sensing and Earth observation have the advantages that they can cover large areas and provides repeated, spatially continuous and standardized information. However, to date it has proven challenging to use these methods to assess small-scaled species-level biodiversity components with this approach. Here we surveyed bees and flowering plants using conventional field methods in 30 grasslands along a land-use intensity gradient in the Southeast of the Netherlands. We took RGB (true colored Red-Green–Blue) images using an Unmanned Aerial Vehicle (UAV) from the same fields and tested whether remote sensing can provide accurate assessments of flower cover and diversity and, by association, bee abundance and diversity. We explored the performance of different machine learning methods: Random Forest (RF), Neural Networks (NNET) and Support-Vector Machine (SVM). To evaluate the effect of the spatial resolution on the accuracy of the estimates, we tested all approaches using images at the original spatial resolution (∼ 0.5 cm) and re-sampled at 1 cm, 2 cm and 5 cm. We generally found significant relationships between UAV RGB derived estimates of flower cover and in situ estimates of flower cover and bee abundance and diversity. The highest resolution images generally resulted in the strongest relationships, with RF and NNET methods producing considerably better results than SVM methods (flower cover RF R2 = 0.8, NNET R2 = 0.79; bee abundance RF R2 = 0.65, NNET R2 = 0.54, bee species richness RF R2 = 0.62, NNET R2 = 0.52; bee species diversity RF R2 = 0.54, NNET R2 = 0.46). Our results suggest that methods based on the coupling of UAV imagery and machine learning methods can be developed into valuable tools for large-scale, standardized and cost-effective monitoring of flower cover and therefore of an important aspect of habitat quality for bees.

Managed and unmanaged floral margins for the conservation of bee communities in intensive agricultural areas

Floral resources on crop field margins are a well-accepted measure to increase bee abundance in agricultural landscapes. However, studies have mainly focused on managed margins, while studies on the effect of unmanaged floral margins for the conservation of bees are still scarce. This work aims to test and compare the effects of three types of floral margins (managed herbaceous, managed shrubby, and unmanaged herbaceous) on the abundance and diversity of bees in order to propose a management strategy for the conservation of pollinating insects. Bee abundance was recorded by visual samplings in plots of 2 × 2 square meters over two years in the three margin types in four localities in southern Spain. The diversity of plant species and the flowers they supported were measured to explain the associated bee communities. Differences in the relative abundances of bee families and the number and abundance of bee genera were observed between margin types. Andrenidae was generally more abundant in the herbaceous margins regardless of whether these were managed or not. With the exception of the Halictidae, the majority of bees families (wild Apidae, Apis mellifera, Colletidae and Megachilidae) were more abundant in the managed than unmanaged margins. Moreover, the number of bee genera was higher in managed than in unmanaged margins. In addition, here we show that managed margins supported at least 30% more rare bee genera than unmanaged margins, highlighting the importance of floral margins management for the enhancement and conservation of bee communities, restoring habitat and food resources for pollinators across the Mediterranean agricultural landscape.

Urbanization and abundance of floral resources affect bee communities in medium‐sized neotropical cities

AbstractBees are important pollinators that have been negatively impacted by anthropogenic environmental changes, such as urbanization. In addition, urban development can reduce and degrade the natural habitat of bees by increasing the proportion of impervious surfaces, decreasing green areas and increasing the number of exotic ornamental plants. However, cities can provide refuge for bees because they provide an environment with a wide variety of nesting and foraging resources. The objective of our study was to evaluate the richness and abundance of bees, their respective functional groups, and community composition along with an urbanization gradient in 21 locations distributed among six medium‐sized Brazilian cities (with populations between 80 000 and 170 000 inhabitants). We also evaluated the effect of richness, number of plants and proportion of native plants. We collected a total of 132 species of bees. Total bee richness decreased with increasing impervious cover and increased with landscape heterogeneity, which also had a positive effect on the richness of above‐ground nesting bees and generalist bees. Regarding abundance data, solitary bees and belowground‐nesting bees were positively influenced by the increase in grass cover. The total number of native and exotic plants collected positively influenced the total abundance of bees, as well as the abundances of eusocial bees, which nest above‐ and belowground, and generalists. The proportion of native plants positively influenced the total richness and abundance of specialist bees. Our results indicate that medium‐sized urban areas may be home to a wide diversity of bee species, but species that nest in the soil and specialist species may be more sensitive to urbanization and the decrease in the supply of floral resources.

Environmental and biotic filters interact to shape the coexistence of native and introduced bees in northern Patagonian forests

Native and introduced species can coexist in rich ecosystems where competition for resources is less intense; however, native species can be excluded from suitable habitats hosting a high abundance of introduced species. To test these hypotheses, we estimated the probability of introduced bees (buff-tailed bumblebees and honeybees) to co-occur and dominate giant bumblebees in forested landscapes of northern Patagonia. We evaluated the effects of 29 remote-sensing variables of forest ecosystems on bee abundance using data from 56 landscapes. Then, we used a probabilistic Bayesian model to estimate the effects of the most important predictors of bee abundance on their co-occurrence and dominance probabilities. Introduced and native bees exhibited heterogeneous and scale-dependent responses to environmental conditions, with only six variables affecting their co-occurrence and dominance probabilities. A high maximum temperature was associated with both a decreased co-occurrence and an increased dominance of introduced bumblebees, and the opposed pattern was found for vegetation continuous fields, an index of canopy continuity. Similar responses were found for the co-occurrence probability of honeybees and giant bumblebees. Thus, species dominance and co-occurrence changed differently along environmental gradients, with co-occurrence increasing as native and introduced species become more abundant. A high dominance of introduced bees in unsuitable habitats suggests interspecific competition is strengthened as resources become scarcer, thus reinforcing the idea that abiotic and biotic filters interact with each other.

Large Remaining Forest Habitat Patches Help Preserve Wild Bee Diversity in Cultivated Blueberry Bush

Global declines in wild and managed bee populations represent a major concern for the agricultural industry. Such declines result, in part, from the loss of natural and semi-natural habitats in and around agricultural ecosystems. However, remaining forest patches in heavily modified landscapes represent nesting habitats that may be crucial to preserving wild bees and their services. Because wild bees are the main pollinators of fruit crops, preserving potential nesting habitats might be particularly important for the crops’ yield and profitability. Here, we assessed whether the abundance and richness of visiting wild bees in blueberry crops relates to the amount of surrounding forest cover and if so, whether those relationships varied with spatial scale. Specifically, we sampled wild bee communities in 18 blueberry fields during the blooming period in Montérégie, Quebec, Canada, where sampling consisted of pan trap triplets and direct observation of flower visitors on blueberry bushes. Then, we quantified the proportion of forest in radii of 0.5 km, 1 km, and 2 km around each field. Wild bee abundance was positively related to the proportion of forest habitat surrounding the crop field, but the relationship for wild bee richness was less clear. Moreover, these relationships were strongest at 1 and 2 km radii of measured land cover. Overall, pollinator diversity was highest when at least 30% of the surrounding landscape consisted of forest patches, representing a total area of at least 1 km2. Our results suggest that preserving large habitat patches in agricultural landscapes can help prevent further decline in wild bee diversity while maximizing pollination services to fruit crops.

Habitat characteristics structuring bee communities in a forest-shrubland ecotone

The relationship between bee community composition and habitat characteristics at local scales may inform management decisions and conservation strategies for species of conservation concern. Ecotones are transition zones between two adjacent habitats that can potentially support abundant and diverse bee communities by providing complementary habitat characteristics within the foraging distance of most bee species. In a forest-shrubland ecotone, we evaluated the relationships between multiple habitat characteristics and the taxonomic and functional diversity of bee communities. Early in the growing season, floral abundance was positively associated with bee abundance but negatively associated with bee richness and functional diversity, indicating that large floral displays increase specialization of common bee species. The abundance of trees within the ecotone was positively associated with coarse woody debris (CWD), and in turn CWD had a positive association with bee richness and functional diversity early in the growing season and positive association with functional richness later in the growing season. Ecological processes within the ecotone that convert trees into CWD may provide resources for aboveground cavity nesting bee species. Late in the growing season soil composition was associated with bee functional diversity. The functional richness of bee communities also had a positive association with the specialization of bee-flower interaction networks, indicating that bee communities with more functional groups contain more specialist bee species. Studies that disentangle the effects of specific habitat characteristics on bee community composition will help identify management strategies that are consistent with bee conservation in ecotone environments.

Declines of bees and butterflies over 15 years in a forested landscape

Despite growing concerns about pollinator declines,1,2,3,4 evidence that this is a widespread problem affecting entire communities remains limited.5 There is a particular shortage of pollinator time series from relatively undisturbed natural habitats, such as forests, which are generally thought to provide refuge to biodiversity from anthropogenic stressors.6 Here, we present the results from standardized pollinator sampling over 15 years (2007-2022) at three relatively undisturbed forested locations in the southeastern United States. We observed significant declines in the richness (39%) and abundance (62.5%) of bees as well as the abundance of butterflies (57.6%) over this time period. Unexpectedly, we detected much stronger declines in the richness and abundance of above-ground-nesting bees (81.1% and 85.3%, respectively) compared with below-ground-nesting bees. Even after dropping the first or last year of sampling, which happened to yield the greatest and lowest numbers of pollinators, respectively, we still detected many of the same negative trends. Our results suggest that sharp declines in pollinators may not be limited to areas experiencing direct anthropogenic disturbances. Possible drivers in our system include increasing mean annual minimum temperatures near our study sites as well as an invasive wood-nesting ant that has become increasingly widespread and abundant in the region over the course of this study.

Forest and grassland habitats support pollinator diversity more than wildflowers and sunflower monoculture

Abstract Intensively managed agricultural landscapes often lack suitable habitats to support diverse wildlife, particularly harming pollinator communities. Besides mass flowering crops, remnant patches of natural and semi‐natural vegetation may play a key role in maintaining and conserving biodiversity. Yet, the effects of different natural habitats, including forests and grasslands, on different pollinator communities are poorly understood at the landscape scale. We examined the abundance, richness, and diversity of wild bees and hoverflies, two key pollinator groups, across a land‐use gradient spanning forest edges, grassland, wildflower strips, and sunflower monoculture. We also examined the distribution of hoverfly larvae trophic guilds and wild bee nesting traits across the above‐mentioned land‐use gradient. Finally, we evaluated the impact of landscape structure (forest, grassland, and water cover in the surrounding landscape) on pollinator community composition. Our results indicate that forest and grassland habitats supported a higher abundance and greater richness of pollinators than wildflower strips and sunflower monocultures. Furthermore, hoverflies were more sensitive to habitat and floristic homogenization than wild bees. Sunflower and wildflower habitats also hosted a lower diversity of larvae trophic guilds and wild bee nesting guilds as compared to forests and grasslands. Our study suggests that conserving and restoring forest and grassland habitats within agricultural mosaics may serve as the main ‘refuge’ for wild pollinators.

Planted pollinator habitat in agroecosystems: How does the pollinator community respond?

Pollinators are important both ecologically and economically. Nonetheless, documented pollinator population decline threatens ecosystem functioning and human well-being. In response, conservation methods such as augmented pollinator habitat are becoming popular tools to combat pollinator losses. While previous research has shown added habitat can benefit bee communities, there are still aspects of the habitat implementation that require further research, particularly how this will impact bee communities in real-world settings beyond researcher-led efforts. In our study, we use a 2016 initiative mandating the planting of pollinator habitat on research stations across North Carolina, United States to act as an outdoor laboratory to investigate this exact question. From 2016 to 2018, we found significant increases in bee abundance and diversity. However, these increases depended on the quality of habitat, with areas of higher flower cover and diversity supporting larger, more diverse bee communities. Although the habitats positively supported bee communities, we found that resources within the habitats were lower later in the sampling season, highlighting the need of developing seed mixes that include late season resources. Weedy plants were documented to establish within the habitats, demonstrating the need for regular upkeep and maintenance of pollinator habitat in order to appropriately support bee communities. It is likely that planting pollinator habitat will not be a one-size-fits-all conservation solution, as bee species can respond differently to some habitat characteristics. Future long-term studies on pollinators will be important as natural fluctuations in bee populations may limit findings and many knowledge gaps on native bees still persist.

Enhanced urban roadside vegetation increases pollinator abundance whereas landscape characteristics drive pollination

Roads cause pollution, habitat degradation and fragmentation, while recent studies report that roadside vegetation can benefit plant and insect diversity. However, the factors that drive effects of roadside vegetation on pollinator abundance and pollination need further attention. Our main interest in this study was to evaluate urban roadside enhancement by identifying direct and indirect effects of local resource availability and landscape characteristics on pollinator abundance and quality of pollination, by using functionally different phytometer plants. Thus, we established 34 species-rich wildflower patches along urban roads, and monitored flowering species and floral density at the local scale. At the landscape scale we measured the amount of impervious surface within a radius of 500 m around the wildflower patches, as well as edge density of all major land-use types, and distance to the city center. As control, we used 34 patches with existing species-poor roadside green. The abundance of pollinators, i.e., honeybees, wild bees, and hoverflies, was sampled with colored pan traps. Pollination was monitored based on fruit number and weight of three phytometer species, i.e., Fragaria × ananassa, Ranunculus acris, and Trifolium pratense, that differ in flower morphology and color, and attract different pollinators. Pollinator abundance was positively related to local richness of flowering plants and floral density. At the landscape scale, pollinator abundance was positively related to the proportion of impervious surface but negatively to edge density. Phytometer-specific effects on pollination were moderated by landscape characteristics: Fruit mass of F. x. ananassa was highest in the inner city, fruit number of R. acris was lower in areas with high edge density, whereas in T. pratense fruit number increased with edge density, and was negatively related with the proportion of impervious surface. There were no indirect effects of local and landscape factors via pollinator abundance on pollination. The study of the three phytometer species revealed that roadside enhancement can directly support fruit production in wild plants and crops in cities. Thereby, different landscape characteristics influenced the quality of fruit set, which also depended on individual plant reproductive adaptations. This stresses the importance of using a set of complementary phytometer species in pollination experiments, especially to gain insights into ecosystem functioning at coarser spatial scales.

Decline in wild bee species richness associated with honey bee (Apis mellifera L.) abundance in an urban ecosystem.

The spatial heterogeneity of urban landscapes, relatively low agrochemical use, and species-rich floral communities often support a surprising diversity of wild pollinators in cities. However, the management of Western honey bees (Apis mellifera L.) in urban areas may represent a new threat to wild bee communities. Urban beekeeping is commonly perceived as an environmentally friendly practice or a way to combat pollinator declines, when high-density beekeeping operations may actually have a negative influence on native and wild bee populations through floral resource competition and pathogen transmission. On the Island of Montréal, Canada there has been a particularly large increase in beekeeping across the city. Over the years following a large bee diversity survey ending in 2013, there was an influx of almost three thousand honey bee colonies to the city. In this study, we examined the wild bee communities and floral resources across a gradient of honey bee abundances in urban greenspaces in 2020, and compared the bee communities at the same sites before and after the large influx of honey bees. Overall, we found a negative relationship between urban beekeeping, pollen availability, and wild bee species richness. We also found that honey bee abundance had the strongest negative effect on small (inter-tegular span <2.25 mm) wild bee species richness. Small bee species may be at higher risk in areas with abundant honey bee populations as their limited foraging range may reduce their access to floral resources in times of increased competition. Further research on the influence of urban beekeeping on native and wild pollinators, coupled with evidence-based beekeeping regulations, is essential to ensure cities contain sufficient resources to support wild bee diversity alongside managed honey bees.