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a Geographic distribution of 12,003 museum specimen records (small points) used to assess rarity for bees in the northeastern USA. In order to associate bee rarity with different land cover types, we collected intensive community samples from 36 sites in forested (large black points), agricultural (gray) and urban (white) landscapes. b Frequency distribution of the maximum monthly abundances of 443 species in the museum data set used to define species rarity classes (light gray bars). Dark bars identify the subset of 226 species observed in our field study, which we classified into rarity categories based on the 25th, 50th, and 75th percentiles (x-axes values mark percentile boundaries)
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ContextThe response of rare species to human land use is poorly known because rarity is difficult to study; however, it is also important because rare species compose most of biodiversity, and are disproportionately vulnerable. Regional bee pollinator faunas have not been assessed for rarity outside of Europe. Therefore, we do not know to what exte...
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Citations
... We predicted higher edge density and mean perimeter-area ratio would be correlated with more diverse pollinator communities because, compared with core forest or adjacent agricultural land, in mid-Atlantic USA, forest edges and hedgerows often have more diverse plant communities with higher floral abundance (Kammerer et al. 2016b;Iverson et al. unpublished data). We expected that landscapes with high diversity of land cover classes would have higher richness of bees because diverse landscapes are more likely to contain habitat specialists and rare species (Harrison et al. 2019). ...
... Additionally, targeted additions or restorations of wetlands and surface-water features provides conservation benefits to spring bees as well as other plant and animal taxa. While late season bees increase in abundance in areas with more summer-flowering plants, in highly agricultural landscapes, improving local quality for late bees will likely primarily benefit disturbancetolerant, generalist species (Harrison et al. 2019). By considering spatial and temporal variation in resources, we developed context and season-specific recommendations to improve habitat quality for wild bees, a critical component of conservation efforts to offset the manifold stressors threatening these taxa. ...
Context
There is great interest in land management practices for pollinators; however, a quantitative comparison of landscape and local effects on bee communities is necessary to determine if adding small habitat patches can increase bee abundance or species richness. The value of increasing floral abundance at a site is undoubtedly influenced by the phenology and magnitude of floral resources in the landscape, but due to the complexity of measuring landscape-scale resources, these factors have been understudied.
Objectives
To address this knowledge gap, we quantified the relative importance of local versus landscape scale resources for bee communities, identified the most important metrics of local and landscape quality, and evaluated how these relationships vary with season.
Methods
We studied season-specific relationships between local and landscape quality and wild-bee communities at 33 sites in the Finger Lakes region of New York, USA. We paired site surveys of wild bees, plants, and soil characteristics with a multi-dimensional assessment of landscape composition, configuration, insecticide toxic load, and a spatio-temporal evaluation of floral resources at local and landscape scales.
Results
We found that the most relevant spatial scale and landscape factor varied by season. Early-season bee communities responded primarily to landscape resources, including the presence of flowering trees and wetland habitats. In contrast, mid to late-season bee communities were more influenced by local conditions, though bee diversity was negatively impacted when sites were embedded in highly agricultural landscapes. Soil composition had complex impacts on bee communities, and likely reflects effects on plant community flowering.
Conclusions
Early-season bees can be supported by adding flowering trees and wetlands, while mid to late-season bees can be supported by local addition of summer and fall flowering plants. Sites embedded in landscapes with a greater proportion of natural areas will host a greater bee species diversity.
... One of the main contributing factors to the current pollinator declines is the alteration and loss of their habitat due to human activity [5,6]. Anthropogenic landscapes present new challenges for the survival and reproduction of organisms, increasing their risk of extinction by maladaptation [7][8][9]. Yet, not all pollinator species are negatively affected by land use change. Indeed, some bee species are able to tolerate human-altered environments [10][11][12] or even to thrive [13,14]. ...
The rapid conversion of natural habitats to anthropogenic landscapes is threatening insect pollinators worldwide, raising concern regarding the negative consequences on their fundamental role as plant pollinators. However, not all pollinators are negatively affected by habitat conversion, as certain species find appropriate resources in anthropogenic landscapes to persist and proliferate. The reason why some species tolerate anthropogenic environments while most find them inhospitable remains poorly understood. The cognitive buffer hypothesis, widely supported in vertebrates but untested in insects, offers a potential explanation. This theory suggests that species with larger brains have enhanced behavioural plasticity, enabling them to confront and adapt to novel challenges. To investigate this hypothesis in insects, we measured brain size for 89 bee species, and evaluated their association with the degree of habitat occupancy. Our analyses revealed that bee species mainly found in urban habitats had larger brains relative to their body size than those that tend to occur in forested or agricultural habitats. Additionally, urban bees exhibited larger body sizes and, consequently, larger absolute brain sizes. Our results provide the first empirical support for the cognitive buffer hypothesis in invertebrates, suggesting that a large brain in bees could confer behavioural advantages to tolerate urban environments.
... Urbanization is considered a major global driver of biodiversity change, with negative impacts on many pollinator species (Theodorou et al. 2020a), including lower flower visitation rates, reduced species richness, species loss and homogenisation, and changes in pollinator and plant phenology (Hernandez et al. 2009;Harrison and Winfree 2015;Harrison et al. 2019). Furthermore, green heterogeneous spaces within urban areas can maintain taxonomic diversity, greater bee diversity, niche complementarity, higher flower visitation rates, and positively increase pollination services (Theodorou et al. 2016;Baldock et al. 2019;Hamblin et al. 2018;2020a, b;Fournier and Moretti 2020;Casanelles-Abella et al. 2021). ...
Bees are the most important pollinators and, like many other insects, are facing a global decline that threatens crop pollination services. Both honey bees and some wild bee species are used commercially for pollination, including pollination in blueberry and cherry orchards. In our study, we assessed bee visits to experimental blueberry and cherry orchards immersed in an urban landscape to understand how air-temperature affects the potential contribution of honey bees and wild bees to pollination services. The potential contribution to pollination services was estimated using the Pollination Importance Value index, where the pollen collected by the floral visitor is a determining variable. In our study, bumble bees and honey bees were the most important floral visitors in the orchards, followed by the wild bee Anthophora plumipes. We found that honey bees were affected by changes in air-temperature and their decrease in the potential contribution to pollination services was offset by the niche complementarity provided by bumble bees.
Implications for insect conservation Even small changes in air-temperature can alter bee communities by affecting bee species susceptible to low temperatures. Our work is a first assessment of how climate change may affect the complementarity of pollinator communities in orchards. We suggest that strategies to mitigate local air-temperature changes in urban areas, focusing primarily on these species, could potentially have cascading effects that would support the overall pollination services provided by bee communities.
... These dominant crop pollinators are generally robust to land-use change, being able to persist even in intensively managed agricultural landscapes, and can relatively easily be promoted by generic, local-scale conservation measures . In contrast, non-dominant or rare bee species are often more susceptible to agricultural intensification and loss of semi-natural habitats (Fijen et al., 2019;Harrison et al., 2019), and the conservation of these species typically requires more targeted conservation measures and landscape-scale approaches (Pywell et al., 2012;Senapathi et al., 2015). ...
... Urbanization has been shown to negatively impact pollinators, particularly bee species (Brant et al. 2022;Harrison et al. 2019;Hernandez et al. 2009). Cities convert natural habitat into paved landscapes, which contribute to a depletion of provisioning and nesting resources that affects bee foraging, fecundity, and overall species richness and abundance (Ayers and Rehan 2021;Cardoso and Gonçalves 2018;Geslin et al. 2016;Potts et al. 2010). ...
... While rapid urbanization around the globe has high impact on wild bee populations (Cardoso and Gonçalves 2018;Geslin et al. 2016;Hernandez et al. 2009;Zipper et al. 2017;Harrison et al. 2019), cities can also support bee diversity, providing refuges for a considerable number of managed and wild bees (Hall et al. 2017;Threlfall et al. 2015;Wilson andJamieson 2019, reviewed in Ayers and. In fact, more bees visit residential and community gardens in the UK than other land types, thus urban areas may be considered pollinator hotspots (Baldock et al. 2019). ...
Urbanization is considered one of the major threats to biodiversity worldwide, with a special concern for native species decline, including wild bees. Through the increase of impervious surfaces, urbanization diminishes, fragments, and warms city environments, significantly reducing nesting and foraging resources for bees. Understanding the response of wildlife to urbanization in terms of reproduction, foraging efficiency, and offspring provisioning is important to species conservation in the face of continued urban development. In this study, we investigated how different levels of urbanization affect individual foraging effort, survival, brood productivity, and fitness in Ceratina calcarata. Our findings show that low urbanization levels favour larger-bodied adults, but foraging efforts (determined by wing wear) were higher at moderate disturbance levels. Larger-bodied mothers produced more numerous offspring (clutch size), mainly in medium disturbance sites. Likewise, larger-bodied mothers produced a larger-bodied offspring at low urbanization levels. Our results indicate that wild bees benefit from low and medium levels of urbanization indicated by maternal and offspring fitness in terms of body size and the number of brood, respectively. This suggests significant effects of urbanization on the fitness and stability of wild bee populations. This study provides novel insights into the impact of urban land use and highlights the importance of conserving and providing green spaces for pollinators.
... Miller-Rushing et al. (2008) recommended sampling every second day to ensure a 97% probability of detecting significant change in date of flowering; they noted however, that for many studies less frequent sampling may be adequate to determine simple trend detection. At the opposite end of the scale, sampling every two weeks was recommended to monitor tropical tree phenology (Harrison et al. 2019). Because the purpose of this study is to give an indication of the number of weeks for which regular grass-cutting should be suspended during spring, a weekly fieldwork protocol was used. ...
Converting road verges and Public Open Space (POS) to floral-rich resources is an important strategy for supporting populations of urban pollinators. One of the ways this can be achieved is through adjusting mowing schedules, either with a “delayed start” after the end of winter, or a reduction in mowing frequency. In Mediterranean climate ecosystems with mild, wet winters, plant growth continues through the winter season and the definition of a “delayed start” is unclear. This study sought to identify a strategic period for the suspension of mowing activities in a city in South Africa with a Mediterranean climate. It estimated the duration of the flowering to seed-broadcast season of 20 species of native geophytes. Observations were made of phenological status from bud to seed broadcast in ten city parks in Cape Town during the austral spring flowering seasons of 2019 and 2020 (August – December). The Underhill and Zucchini (1988) Moult Model was employed to estimate the duration of the flowering season. Model results showed that mowing should stop in the second week of August and should not resume until the beginning of November in the study context. The results are discussed against the relative biodiversity contribution that different parks and verges make and the potential conflicts with the utility objectives of urban society.
... Increasing urbanisation through urban densification and expansion may reduce pollinator richness, lower flower visitation rates, and reduce the diversity of interactions between plants and flower visiting insects due to landscape fragmentation and habitat loss (Udy et al. 2020;Harrison et al. 2019;Deguines et al. 2016;Bates et al. 2011) -with potential cascading effects on pollination services (Theodorou et al. 2021;Aguilar et al. 2006;Cheptou and Avendaño 2006; but see also Verboven et al. 2014b), as urbanization often drives the loss of nesting and floral resources (Theodorou et al. 2020a, b;Harrison and Winfree 2015;Williams et al. 2010). However, at the local habitat scale, the availability of floral resources, namely floral richness and abundance can have a positive effect on plant-pollinator interactions (Udy et al. 2020), pollinator diversity (Tasker et al. 2020;Woodard and Jha 2017;Wojcik and McBride 2012;Potts et al. 2003), flower visitation frequency (Gilpin et al. 2022;Ebeling et al. 2008;Hegland and Boeke 2006) and pollen deposition (Monasterolo et al. 2022;Cohen et al. 2021). ...
Pollinating insects are essential for food production. Both bee and non-bee pollinators are undergoing dramatic declines due to land use intensification and its consequences on native ecosystems. While interactions between crops and bee pollinators are well studied, our understanding of the pollination service provided by non-bee flower visitors including flies, ants, beetles and others is still limited. Moreover, the effects of landscape urbanization and changes in floral and nesting resource availability on the network structure of pollinators with both cultivated and wild plants have been poorly studied. We assessed which common bee and non-bee flower visitor groups dominate the interactions with both wild (e.g. Trifolium pratense, Taraxacum officinales) and cultivated plants (e.g. Fragaria ananassa, Cucurbita pepo) in urban community gardens in Berlin and Munich and explored how these interactions between flower visitor groups and plants change over the growing season. We further investigated the effect of changes in urbanization surrounding community gardens, and the availability of floral and nesting resources within gardens on the complexity (i.e. nestedness, linkage density, connectance) of interaction networks. We observed 20 focal plant species and 13 common bee and non-bee flower visitor groups in 30 urban community gardens. We found that dominant plant visitors changed over the growing season, with non-bee flower visitors including ants and flies as dominant early season visitors, and bee pollinators as important visitors later in the season. Nestedness of the flower visitor network increased with increases in floral richness in community gardens, while neither floral abundance nor the impervious surface surrounding the community gardens, garden size or the availability of nesting resources in gardens strongly influenced the flower visitor networks. Our findings suggest that high floral richness in community gardens may ensure the complexity and, thus, the stability of flower visitor networks. Findings further suggest that the role of non-bee flower visitors should be considered for pollination service provision especially in the shoulder seasons. Finally, our results emphasize that urban gardeners play a key role in mediating flower visitor interactions through their gardening practices.
... While rare species are not always at risk (Vermeij and Grosberg, 2018), the fossil record indicates they are more prone to extinction (Harnik et al., 2012) and may be particularly sensitive to habitat loss and fragmentation caused by human activity (Davies et al., 2004;Sykes et al., 2020). In the Eastern US, human-dominated landscapes support fewer rare bees than native forest habitats (Harrison et al., 2019), and intensive land use around native forest fragments can reduce the abundance of rare bee species (Volenec and Smith, 2021). ...
Managing and restoring tallgrass prairie ecosystem is an important form of pollinator conservation in the Midwestern United States. Prairie reconstruction has been found to enhance native bee diversity and abundance, but it is less clear if prairie reconstruction conserves species thought to be at-risk. We reanalyze a previously published dataset on the bee communities of reconstructed and remnant prairie in the US state of Minnesota to investigate how the abundance of at-risk species respond to local factors, such as floral diversity and prairie type (reconstructed or remnant), and landscape factors, in the form of surrounding agricultural production. We defined at-risk species in two ways. For bumble bees, we used the IUCN red list of bumble bees for North America. As other species in the bee community have not been systematically evaluated, we used an independent data set to calculate a community-level measure of rarity as a proxy for species risk. We calculated community rarity metrics using a Species Weighted Mean (SWM) approach, with species level rarity (relative abundance and site occurrence) derived from a regional dataset comprised of over 30,000 specimens from across the US state of Minnesota. We found that the declining bumble bee Bombus fervidus had higher abundances in remnant rather than reconstructed prairies. Floral richness was associated with rarer bee communities (lower SWM values) across remnant and reconstructed prairies. We show that planting and managing prairies for floral diversity promotes bee communities with rarer species, but that remnants better support some at-risk species such as Bombus fervidus.
... Humans have been altering North American ecosystems for thousands of years (Denevan 1992), but anthropogenic disturbance accelerated post-European colonization to the extent that human land use is the primary cause of reduced terrestrial biodiversity (Pereira et al. 2010;Harrison et al. 2019;Wang et al. 2021). Urbanization has also steadily increased globally from 1992-2018, and urban development is expected to continue to displace natural vegetation (Radwan et al. 2021). ...
With increased population growth and suburban sprawl, anthropogenic landscapes such as urban ecosystems are becoming increasingly abundant, with changes in land cover contributing to loss of biodiversity and ecosystem functions. As such, it is important to understand how land cover choices impact ecosystem services and functions within urban ecosystems. Turf grass lawns are the default landscape in North America, but recent efforts have focused on replacing lawns with native plant communities. Native plant communities within urban ecosystems increase abundance and diversity of insects and insectivorous birds, but less is known about how native gardens could impact underlying soil bacterial communities. In this study, we identified 13 sites in the Omaha/Lincoln, Nebraska, USA area with native plant gardens that were converted from turf grass. We collected soil samples in October, 2020 (n = 18 native garden soil samples and n = 13 turf grass samples) and isolated DNA for high throughput sequencing. We compared the bacterial community structure, bacterial diversity, and individual bacterial taxa between native plant gardens and adjacent turf grass. We found several potentially beneficial bacterial taxa to be more abundant in native garden soil than in adjacent turf. The genera Gemmatimonas, Kofleria, and Acidobacteria belonging to Subdivision3 genera incertae sedis, were significantly more abundant in native garden soils, while Solirubrobacter was significantly more abundant in turf grass soils. Kofleria has been suggested as a keystone taxon for rich organic soils, while greater abundance of Gemmatimonas in native garden soils indicates a high level of soil carbon and phosphorous sequestration and functions as a potential sink for the greenhouse gas nitrous oxide. Native gardens also supported significantly more bacterial biodiversity than adjacent turf. These findings suggest that conversion of turf grass to native gardens could improve ecosystem services associated with soil bacterial diversity such as increased carbon sequestration, phosphate dissolution, and soil reduction of nitrous oxide.
... As such, although small sections of conservation habitat can be beneficial, it is essential to consider optimal spatial configuration of these sections to avoid "doing more harm than good". In comparison with the density of research on pollinator conservation schemes for rural (primarily agricultural) environments (Albrecht et al., 2020;Holzschuh et al., 2016), urban pollinator ecology have remained largely under-researched (Harrison et al., 2019;Hicks et al., 2016). Small-scale conservation efforts like those we have detailed here are likely more suitable for urban (or anthropogenic) environments, due to a lack of expansive areas for conservation schemes commonly found in rural space. ...
... Small-scale conservation efforts like those we have detailed here are likely more suitable for urban (or anthropogenic) environments, due to a lack of expansive areas for conservation schemes commonly found in rural space. Urban landscapes support fewer rare bee species than natural landscapes, and in many cases worldwide, urbanization and nutritional stress have collectively contributed to declines (Harrison et al., 2019;Penick et al., 2016). With significant "grass roots" efforts within communities, urban environments can support native solitary bee communities (Prendergast, 2021). ...
Insect pollinators are declining globally as a result of the anthropogenic pressures that have destroyed native habitats and eroded ecosystems. These declines have been associated with agricultural productivity losses, threatening food security. Efforts to restore habitat for pollinators are underway, emphasizing large-scale habitat creation like wildflower strips, yet ignoring the impact of smaller or more isolated patch-creation.
A meta-analysis of 31 independent published studies assessed the effect of scale of pollinator planting interventions (herbaceous strips, hedgerows, fertiliser/grazing/mowing control). We assessed pollinator species richness and abundance against size of intervention and type. Pollinator conservation interventions increased species richness and abundance in almost all of the studies examined, with the greatest increases in pollinator ecological metrics seen from hedgerows covering 40 m² and herbaceous interventions at 500 m².
We then analysed results from a 5-year study that deployed small pollinator habitats (30 m²) at community gardens and farms (<150,000 m²) practicing organic methods in the Pacific Northwest US. Small additions to pollinator resources had a significant local impact on pollinator abundance, but this effect was lost when these relatively small additions were introduced to sites in larger landscapes (>150,000 m²).
Together, we show that small interventions (∼500 m²) can significantly benefit pollinators, but only when sufficiently densely distributed at a landscape level. Though we understand the effects of single interventions at various scales, future research is needed to understand how these relatively small interventions act cumulatively at a landscape scale, and within this context whether larger areas are still needed for some species. Nonetheless, these preliminary data are promising, and may play an important role in convincing smaller landowners to act to preserve insect pollinators.
