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Abstract

Honeybees might outcompete wild bees by depleting common resources, possibly more so in simplified landscapes where flower-rich habitats have been lost. We tested this by experimentally adding honeybee hives to nine sites while ensuring that ten additional sites were free from hives. The landscape surrounding each geographically separated site either held low (homogeneous landscape) or high (heterogeneous landscape) proportion of semi-natural grasslands. Adding honeybees suppressed bumblebee densities in field borders and road verges in homogeneous landscapes whereas no such effect was detected in heterogeneous landscapes. The proportional abundance of bumblebee species with small foraging ranges was lower at honeybee sites than at control sites in heterogeneous landscape, whereas bumblebee communities in homogeneous landscapes were dominated by a single species with long foraging range irrespective of if honeybees were added or not. We conclude that honeybees can impact bumblebee densities, but that landscape heterogeneity modified this effect.

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... Additionally, Henry and Rodet (2018) found that distance to the apiaries controlled honeybee visitation rates rather than the number of hives in the apiaries and, thereby, the degree of competition for floral resources with wild bees at a distance up to 1100 m from the apiary. A Swedish study by Herbertsson et al. (2016) indicates that the flower richness of a landscape is important for the degree of competition between short-ranged bumble bee species and honeybees. Some simple foraging models for bees have been developed (e.g. ...
... Conceptually, competition from honeybees is assumed to depend on four factors: (1) the total number of foraging trips leaving the apiary (Henry and Rodet, 2018); (2) the foraging range of the honeybees (Henry and Rodet, 2018); (3) the area covered by floral resources in the landscape (Herbertsson et al., 2016); (4) the no effect intensity of foraging honeybees that does not result in resource competition with wild bees. The first three factors determine the impact in terms of the intensity of foraging honeybees in the flowers. ...
... The honeybees also disperse among the flowers. Hence, if the ground cover density of flowers is limited the honeybees will concentrate on this area and thereby increase the competition with wild bees as identified by Herbertsson et al. (2016). Contrarily, when flowers are more abundant, the honeybees will disperse over the area, resulting in less resource competition. ...
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This paper suggest an area model to assess the risk of negative effects on wild bees due to food competition from honeybees. The model includes four factors: (1) the total number of foraging visits by honeybees per day; (2) the foraging range of the honeybees, typically measured as a mean or median value; (3) the area covered by floral resources in the landscape; (4) the tolerable competitive pressure posed by honeybees, i.e. the no effect intensity of foraging honeybees per flowering area below which adverse effects on wild bees due to competition will not occur. However, the need of knowing the foraging range (factor 2) is eliminated in the final model using a worst-case approach. As the honeybees from an apiary disperse into the landscape, the distance between the honeybees increases, leading to a decrease in the competitive pressure. Close to the apiary, the competition may exceed the no effect level, leading to the risk of negative effects on wild pollinators, while the competition will decrease below the no effect level further away from the apiary. The model predicts the distance from the apiary needed to keep the density of foraging honeybees below no effect level to avoid competition with wild bees. In spite of rather high spatial complexity, the final model becomes simple and defines a load factor as a ratio between the number of foraging trips and the carrying capacity of the landscape.
... Urban beekeeping positively impacts agricultural functions, such as pollination, honey production, community building, environmental education, and ecosystem sustainability [11,12]. However, there is mounting evidence of the negative impacts of urban beekeeping on ecosystem services [8,13,14]. Governance is critical for minimizing the negative aspects and maximizing the positive aspects of urban beekeeping [15,16]. ...
... While positive impacts of beekeeping, such as food production, pollination functions, community building, and environmental education, have been widely recognized in recent years, various negative aspects of urban beekeeping have also been recognized [8,13,14,31,32]. The data we collected revealed that current urban beekeeping rules may be biased towards resident safety and do not adequately address the negative aspects of urban beekeeping. ...
... In addition to honey bees, various insects, butterflies, and birds also use nectar and pollen. Thus, the presence of many honey bees in urban areas can potentially harm these other flower users [8,13,14]. Some studies have demonstrated negative impacts of beekeeping on native pollinators [8,35,36]. ...
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Urban beekeeping is gaining salience worldwide. Though beekeeping brings benefits to humanity, it has certain negative aspects. We conducted surveys in eight countries where urban beekeeping is practiced to understand the status of the governance of urban beekeeping. There were a wide variety of rules, ranging from detailed ones to the absence of any. The organizations creating regulations included regional governments, basic governments, and even NGOs. Regulatory items for urban beekeeping were biased toward safety, with few regulations of the other aspects, such as biodiversity conservation and apicultural production. We found a wide range of numerical provisions for this regulation type, with no scientific basis provided, and there is further need for improvements.
... Honey bee colony densities were comprised between 0 and 28 colonies within 500m buffers around sites and between 7 and 53 colonies within 1000m buffers around sites (S1 Data). We chose to use the number of honey bee colonies around sites as it has been previously reported to be a good proxy to study potential competitive pressure exerted by honey bees on the wild pollinating fauna [11,18,21,22]. From May to July 2014 and from April to July 2015 and 2016, we carried 8, 11 and 13 observation rounds per green space respectively, spaced out at least by a week. ...
... Here, we found a negative relation between wild pollinator foraging activities and honey bee colony densities but the intensity of this relation could be modulated by the amount of resources available that could be less abundant in early spring or late summer for example. In this study, the proxy we did use to study the potential impact of honey bees on the wild fauna was the density of honey bee colonies around our sites, and this proxy has been used in several other studies [18,22]. We did not however find any significant correlations between the visitation rate of honey bees and the visitation rate of wild pollinators. ...
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As pollinator decline is increasingly reported in natural and agricultural environments, cities are perceived as shelters for pollinators because of low pesticide exposure and high floral diversity throughout the year. This has led to the development of environmental policies supporting pollinators in urban areas. However, policies are often restricted to the promotion of honey bee colony installations, which resulted in a strong increase in apiary numbers in cities. Recently, competition for floral resources between wild pollinators and honey bees has been highlighted in semi-natural contexts, but whether urban beekeeping could impact wild pollinators remains unknown. Here, we show that in the city of Paris (France), wild pollinator visitation rates are negatively correlated to honey bee colony densities present in the surrounding landscape (500m –slope = -0.614; p = 0.001 –and 1000m –slope = -0.489; p = 0.005). Regarding the morphological groups of wild pollinators, large solitary bee and beetle visitation rates were negatively affected by honey bee colony densities within a 500m buffer (slope = -0.425, p = 0.007 and slope = - 0.671, p = 0.002, respectively) and bumblebee visitation rates were negatively affected by honey bee colony density within a 1000m buffer (slope = - 0.451, p = 0.012). Further, lower interaction evenness in plant-pollinator networks was observed with high honey bee colony density within a 1000m buffer (slope = -0.487, p = 0.008). Finally, honey bees tended to focus their foraging activity on managed rather than wild plant species (student t-test, p = 0.001) whereas wild pollinators equally visited managed and wild species. We advocate responsible practices mitigating the introduction of high density of honey bee colonies in urban environments. Further studies are however needed to deepen our knowledge about the potential negative interactions between wild and domesticated pollinators.
... Large honeybee densities can enhance competition between wild bees and honeybees [4][5][6] , particularly when resource availability is low 7 , although the interplay of other factors (e.g. spatial and temporal context 7,8 ) complicates the picture. Nonetheless, although data is still scarce, the rapid, unregulated increase of urban beekeeping in a growing number of cities worldwide (e.g. ...
... Urban beekeeping is a relatively new activity, yet there is a lack of regulation concerning sustainable densities, and increased beehive densities might have negative effects on biodiversity and on honeybees themselves. High densities of honeybee hives have been shown to deplete existing resources in natural 4 and agricultural 8 areas, ultimately negatively affecting other an even more complex situation. Honeybees are not spatially limited and can exploit the available resources freely, regardless of ownership. ...
Article
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Urban beekeeping is booming, heightening awareness of pollinator importance but also raising concerns that its fast growth mightexceed existing resources and negatively impact urban biodiversity. To evaluate the magnitude of urban beekeeping growth andits sustainability, we analysed data on beehives and available resources in 14 Swiss cities in 2012–2018 and modelled thesustainability of urban beekeeping under different scenarios of availablefloral resources and existing carrying capacities. We foundlarge increases in hives numbers across all cities from an average 6.48 hives per km2(3139 hives in total) in 2012 to an average10.14 hives per km2(9370 in total) in 2018 and observed that available resources are insufficient to maintain present densities ofbeehives, which currently are unsustainable.
... There are studies that indicate competition between honey bees and native insect pollinators, especially in landscapes with low plant diversity, between species (Herbertsson et al. 2016;Ropars et al. 2019) but there are also indications that what is good for honey bee colonies is also good for native pollinating insects when there is sufficient habitat provided for all (Evans et al. 2018). Beefriendly habitat increased wild bee success and wild bee success correlated with honeybee success in a study by Evans et al. (2018). ...
Article
Plant VOCs are signaling compounds that attract pollinators, protect plants from stress, disease and predation, have allelopathic effects and play a role in plant growth and development. The purpose of this review was to evaluate pollinator plants for secondary metabolite VOCs such as monoterpenes and sesquiterpenes for their potential medicinal value to pollinating insects. To address disease pathogens impacting native pollinators and honeybees, plants with medicinal VOCs can be selected for prairie strips and pollinator gardens as agricultural best management practices. Eight flowering plants - bee balm, echinacea, catmint, prairie rose, lavender, thyme, oregano and red clover contain VOCs in their nectars and pollens such as caryophyllene, myrcene, germacrene, cymene, thymol, cineol, carvacrol, borneol, nonanal, linalool and terpineol that offer antimicrobial, antifungal, anti-inflammatory, antioxidant benefits and some are acaricides that may aid in controlling the Varroa destructor mite (=jacobsoni).
... This is especially the case for C. hederae as they are active in early autumn and forage on the main source of nectar and pollen for most pollinator species active at this time. There is growing evidence that Apis mellifera (Hymenoptera: Apidae) can compete with wild bee species for floral resources (Hudewenz and Klein 2015;Herbertsson et al. 2016) in part due to them being generalist foragers (Köppler et al. 2007) and living in large colonies. Their diverse diet, and the fact that A. mellifera are known to forage heavily on H. helix during the autumn (Garbuzov and Ratnieks 2014) mean that they make for an ideal comparison between the specialist C. hederae and can help give an indication of the floral resources available in the surrounding area as they are able to forage across large distances (Couvillon et al. 2014). ...
Article
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Colletes hederae, the ivy bee, (Hymenoptera: Colletidae) has undergone large range expansions in Europe in recent years, including colonising Britain in 2001 with its original distribution limited to Western mainland Europe and the Channel Islands. It is thought to specialise on Hedera helix L. (Apiales: Ariliaceae), common ivy. However, some research has questioned this dependence. This study quantifies the foraging ecology of C. hederae to determine its relationship with ivy in Sussex. We quantified the phenology of ivy bloom, C. hederae activity and flower visitation, and pollen collection of females through pollen analysis. We also gathered equivalent data on Apis mellifera both as a comparison and to assess alternative pollen sources. The phenology of female C. hederae activity was highly correlated with and phonologically contained within the ivy bloom period. Pollen analysis from C. hederae identified ivy pollen was 98.5% of samples, significantly more than for A. mellifera (90%). Two other plant species were identified and more common in C. hederae samples when ivy bloom was not at its peak. Surveys of ivy flowers surrounding the aggregations found that C. hederae were the most common insect (26%) foraging on ivy . Although C. hederae can forage on other species, ivy was found to be an important floral resource. The results also suggest the potential for competition with A. mellifera , the only other bee present in more than small numbers on H. helix flowers, as although A. mellifera is a generalist, in autumn it mainly forages on ivy.
... At least for this specific bumble bee species niche differentiation is not prominent enough to attenuate interspecific competitive interactions with honey bees. Indeed the focal species has an overlap in flower choice 8,13 , and food resource depletion by honey bees can be expected for this species, especially in simplified landscapes 49 . But also in the urban context bumble bee flower visitation rates are negatively correlated to honey bee hive densities 50 . ...
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Wild bees are in decline on a local to global scale. The presence of managed honey bees can lead to competition for resources with wild bee species, which has not been investigated so far for human-modified landscapes. In this study we assess if managed honey bee hive density influence nest development (biomass) of bumble bees, an important trait affecting fitness. We hypothesize that domesticated honey bees can negatively affect Bombus terrestris nest development in human-modified landscapes. In Flanders, Belgium, where such landscapes are dominantly present, we selected 11 locations with landscape metrics ranging from urban to agricultural. The bee hive locations were mapped and each location contained one apiary dense (AD) and one apiary sparse (AS) study site (mean density of 7.6 ± 5.7 managed honey bee hives per km2 in AD sites). We assessed the effect of apiary density on the reproduction of reared B. terrestris nests. Reared B. terrestris nests had more biomass increase over 8 weeks in apiary sparse (AS) sites compared to nests located in apiary dense (AD) sites. This effect was mainly visible in urban locations, where nest in AS sites have 99.25 ± 60.99 g more biomass increase compared to nest in urban AD sites. Additionally, we found that managed bumble bee nests had higher biomass increase in urban locations. We conclude that the density of bee hives is a factor to consider in regard to interspecific competition between domesticated honey bees and bumble bees.
... Although grazing is known to influence insect abundance and diversity, Sjödin et al. (2008), in their study in central Sweden, showed that diversity and abundance of bees and butterflies were not affected by grazing intensity to the same extent as it affected hoverflies (Syrphidae) and beetles. Increase in abundance of bees under high levels of grazing has been previously reported (Vulliamy et al. 2006) where it is also suggested that the increased bee abundances at high grazing levels may not be due to changes in floral resources but could be a result of a few genera that could drive these abundance values (Herbertsson et al. 2016, O'Brien and Arathi 2018, O'Brien and Arathi 2019. This can explain the high abundance of Lasioglossum in our study and being semi-social, Lasioglossum may also have a competitive advantage over other solitary bee genera (Michener 1974, Cane 2015, Wilson and Carril 2015. ...
Article
Recent reports indicate that global insect populations are drastically declining, and amongst insects, bees have attracted significant attention. Decades of research on causal factors for bee population declines, indicate that extensive loss of natural habitats resulting from urbanization and agricultural intensification, has led to a dearth of critical nesting and forage resources essential for the sustenance of bees. To address these concerns and to meet the growing need for food production, simple but effective farm management practices such as restoring habitat diversity through planting pollinator habitats along field margins and underutilized areas, revegetating retired farmland with wildflowers and including pollinator-friendly forbs in cover crop mixes, have been recommended. Earlier studies have provided evidence that planting pollinator habitats along field margins and revegetating retired farmland are indeed viable ways to sustain bee pollinators. Here we report results of a case study exploring the benefits of cover cropping with a pollinator-friendly forb mix. Our results indicate that cover cropping to support pollinators can be effective, particularly when cover crops are retained until the flowering stage and that grazing of cover crops could extend support to those genera of bees that prefer grazed areas. Although the reports on global insect declines are dire, our studies show that pollinator-friendly farm management practices can offset the declines and play a significant role in supporting pollinator populations. Regular assessment of the efficacy of these practices will enable us to target efforts towards better implementation of habitat conservation programs.
... Simply increasing the number of managed bee colonies in crop fields is presumably not the optimal solution for pollination management because this would result in higher costs for farmers and high managed bee densities may negatively affect wild bees (Herbertsson et al., 2016;Mallinger et al., 2017). As an alternative, the selection of pollinator species and adaptation of colony size may be more efficient in directing foraging bee pollinators to crops in agricultural landscapes. ...
Article
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Worldwide pollinator declines lead to pollination deficits in crops and wild plants, and managed bees are frequently used to meet the increasing demand for pollination. However, their foraging can be affected by flower availability and colony size. We investigated how mass-flowering oilseed rape (OSR) can influence the pollen resource use of small and large honey bee (Apis mellifera L.) and bumble bee (Bombus terrestris L.) colonies. Colonies were placed adjacent to strawberry fields along a gradient of OSR availability in the landscapes. We used ITS2 metabarcoding to identify the pollen richness based on ITS2 amplicon sequencing and microscopy for quantification of target pollen. Bumble bees collected pollen from more different plant genera than honey bees. In both species, strawberry pollen collection decreased with high OSR availability but was facilitated by increasing strawberry flower cover. Colony size had no effect. The relationship between next-generation sequencing-generated ITS2 amplicon reads and microscopic pollen counts was positive but pollen type-specific. Bumble bees and, to a lesser degree, honey bees collected pollen from a wide variety of plants. Therefore, in order to support pollinators and associated pollination services, future conservation schemes should sustain and promote pollen plant richness in agricultural landscapes. Both bee species responded to the availability of flower resources in the landscape. Although honey bees collected slightly more strawberry pollen than bumble bees, both can be considered as crop pollinators. Metabarcoding could provide similar quantitative information to microscopy, taking into account the pollen types, but there remains high potential to improve the methodological weaknesses.
... (Smith and Lundholm, 2012;Stein and Kreft, 2015). Ainsi, l'hétérogénéité environnementale permet de surmonter les effets négatifs de l'exclusion compétitive sur la richesse de la communauté (Herbertsson et al., 2016). ...
Thesis
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La connaissance des patrons de diversité des communautés d’insectes herbivores occupe une part importante dans la recherche écologique. Elle est nécessaire en vue d’une lutte biologique, sachant que certains insectes herbivores sont capables de devenir des ravageurs de cultures. Les ennemis naturels et les variables environnementales font partie des facteurs structurant les communautés d’insectes herbivores. Alors que les ennemis naturels assurent la régulation des insectes herbivores, les variables environnementales vont plutôt influencer leur diversité et leur distribution spatiale. L’objectif principal de cette thèse était de comprendre les effets des traits de paysage sur la diversité des communautés de thrips herbivores suivant le gradient altitudinal de La Réunion et d’étudier les effets de la diversité des ennemis naturels dans le contrôle biologique des thrips ravageurs. Dans la première étude, les thrips ont été échantillonnés suivant des gradients d'altitude répliqués, et à chaque site d'échantillonnage, les caractéristiques du paysage et les variables abiotiques ont été estimées dans des zones tampons entourant le site. L’étude a révélé que la plus grande diversité des thrips à La Réunion se concentre en basse altitude, bien que les habitats dans ces altitudes soient fortement dégradés. La diversité des thrips a été particulièrement insensible à la fragmentation et, l’hétérogénéité du paysage et la quantité d’habitat ont interagi pour affecter positivement la diversité des thrips. Dans la deuxième étude, nous avons manipulé dans des cages placées sous serre, des communautés composées de deux thrips ravageurs, Thrips parvispinus et Frankliniella occidentalis, et deux espèces d’acariens prédateurs Amblyseius swirskii et Proprioseiopis mexicanus. L’étude a montré que deux prédateurs assurent une meilleure régulation qu’un seul prédateur, confirmant ainsi l’importance de maintenir de la biodiversité au niveau trophique supérieur dans le contrôle biologique des herbivores. Par ailleurs, l’étude a révélé l’existence possible d’un compromis entre la compétition pour la ressource et la dispersion chez les prédateurs, appelé «The, competition-colonization trade-off », permettant ainsi leur coexistence malgré leur interaction dans une prédation intraguilde.
... While tackling climate change would be the obvious, albeit extremely challenging, solution to conserve bumblebee diversity (Kerr et al. 2015;Soroye et al. 2020), indirect effects of climate change, such as reduced forage resources (Ogilvie et al. 2017;Rasmont & Iserbyt 2012) and changed competitive advantages, can possibly be mitigated by the provision of additional resources (c.f. Herbertsson, Lindström, Rundlöf, Bommarco & Smith 2016). In order to take appropriate actions to conserve bumblebees it is therefore important to disentangle the components behind the effect of climate warming on bumblebee communities. ...
Article
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While many bumblebee species decline due to climate and land-use changes, others cope well with contemporary conditions. One example is Bombus terrestris, which is common in intensively managed agricultural landscapes. During the 20th century its subgenus, which includes the B. lucorum complex (B. lucorum, B. cryptarum and B. magnus) came to dominate Scandinavian bumblebee communities, but the specific contribution of B. terrestris remains to be understood. Using historical data on males, we assessed how the relative abundances of B. terrestris and the B. lucorum complex changed over the past 150 years in southernmost Sweden. We tested if these changes differed between simplified and mixed landscapes and whether the relative abundance of B. terrestris was related to annual mean temperatures. Because floral availability has advanced as a response to climate change, we also tested if the activity period of males (estimated as catching date) has advanced and whether the advancement differs between taxa. The relative abundance of B. terrestris increased similarly in both landscapes, from 21% to 79% over the period, and this was largely explained by increasing temperature. Male activity period has advanced similarly in the two taxa, with 41 days between 1900 and 2015. Although the dominance of B. terrestris correlates clearly with annual mean temperature, it remains to disentangle why. It also remains to understand whether the success of B. terrestris occurs at the expense of other species or simply reflects that this species copes better with contemporary conditions.
... A. mellifera does not rely on native grasslands for habitat, and tends to be a dominant species when it is present. Several studies have shown that A. mellifera can have negative effects on the wild bee community (Walther-Hellwig et al. 2006;Herbertsson et al. 2016;Graystock et al. 2014;Lindstrom et al. 2016). Even if restoration efforts improve habitat for native bees, the presence of A. mellifera may swamp out any benefits. ...
Article
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Natural grasslands are being destroyed at an alarming pace, but land managers are actively working to restore these habitats. Many of these efforts focus on restoring plant diversity but often do not consider responses of higher trophic levels such as pollinators, which provide crucial ecosystems services. We conducted a meta-analysis of 25 large-scale studies to examine the effects of grassland restorations on pollinator communities. Specifically, we compared pollinator communities in restored, degraded and remnant grasslands to determine if restorations improve pollinators from a degraded state and if they fully restore them to remnant values. We found that grassland restorations significantly improved both pollinator abundance and richness as compared to degraded grasslands. Additionally, pollinator abundance and richness did not significantly differ from remnant sites, indicating a near full recovery. Sub-analyses found that factors such as pollinator taxa, restoration age, and mode of land degradation all influenced the magnitude of recovery. In particular, lepidopteran abundance increased more than bee abundance in these restorations. Older restorations (> 10 years) showed the strongest improvements in pollinator communities. This research highlights the importance of grassland restorations in supporting not only plant diversity but also pollinators.
... Ultimately, it also points towards allowing bees more autonomy over the lifecycle of their colony, as some beekeepers are aspiring to do, through practices such as allowing colonies to replace the queen and allowing bees to swarm, which, along with presenting particular conceptual challenges and opportunities, 21 problematizes the status of honeybees as commodities that are owned by an individual beekeeper. Although there are concerns about honeybees competing with native bees (Colla & MacIvor, 2016), there are also hopeful indications that all bees can flourish when given access to an abundance of forage (Herbertsson, Lindstrom, Rundlof, Bommarco, & Smith, 2016). ...
Article
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The growing crisis of bee health has shone a spotlight on the problems facing pollinator populations in many parts of the world, the worrying implications for agriculture and ecosystems, and some of the risks of pesticides. Although this attention is important and can open a range of critical vistas, the threats to bees, other pollinators, and the future of pollination are too often framed in narrow ways. The goal of this paper is to provide a systematic way of thinking about the crisis of bee populations by examining the changing dynamics of pollination within industrial agriculture, drawing heavily on transformations in the United States and Canada. We set out a case for understanding pollination as a biophysical barrier to industrial organization and the rise of pollination services as a response that temporarily fixes (or overrides) this barrier, while containing an internal set of contradictions and overrides. We argue that these dialectic relations are continually generating further problems and hope that this lens can help inform critical education, outreach, and movement building with respect to the urgent problems of bee and pollinator health. In particular, we stress the need to connect growing bee‐related advocacy with struggles to confront industrial capitalist agriculture.
... In most European agricultural landscapes, August is a seasonal challenge for flower foragers (Couvillon et al., 2014a), and the landscape in which our study is set is no exception: main resources present were Casteanea sativa and Rubus spp., but only in small quantities (Dervenn, 2013). In such a context, competition for available flower resources may be greater (Couvillon et al., 2014a;Herbertsson et al., 2016). Further studies on the effect of landscape on interactions between wild and managed pollinators at resource shortage periods would greatly improve our understanding of impacts of beekeeping practices throughout the year. ...
Article
Resource partitioning is a key ecological mechanism allowing species sharing similar resources to limit competition and coexist. Pollinator communities in European agricultural landscapes are ideal models to study resource partitioning, as floral resources are often limited and honeybees, potential competitors, are widespread. Mass-flowering crops can provide abundant resources to pollinators, but spatio-temporal exploitation and resource use by wild pollinators in the presence of a managed competitor is poorly studied. Understanding how wild flower-visiting insects can exploit resources provided by crops under high honeybee abundances is primordial to tailor our management strategies to the conservation of those beneficial insects. In this study, we explored the spatio-temporal resource exploitation of four pollinator morphogroups (the honeybee Apis mellifera, small wild bees, large wild bees and hoverflies) on two uncommon monospecific summer flower crops (cornflower and arnica) in an environment containing a high density of honeybee hives. Our results showed that Apis mellifera was the dominant flower visitor; wild pollinators were also present, but most of them were common and generalist foragers. Moreover, results demonstrated a differential use of the flower crops by the four morphogroups: hoverflies foraged earlier in the day compared to honeybees, and wild bees exploited preferentially cornflower extrafloral nectaries, which are spatially separated from the flowerheads, while honeybees preferred floral resources. Intensive extrafloral nectar visitation by wild bees was a surprising result and may be a mechanism limiting exploitative and interference competition with honeybees. Our study urges to consider simultaneously the quality of the flowers to implement and the potentially negative outcomes of intensive beekeeping practices to sustain wild pollinator communities in agroecological landscapes.
... Focal species Competitor Type experiment Result [49] Agricultural (Europe) Bombus spp. Apis mellifera (M) Addition Reduced Bombus foragers only in homogeneous landscapes [50] Agricultural (Europe) Flying insects Apis mellifera (M) Addition Reduced wild insect density, more strongly in large fields [51] Scrubland (Asia) Native bees Apis mellifera (M) Addition Lower native visitation in 3 of 4 years, but not for all plant species [52 ] Scrubland (Europe) All pollinators Apis mellifera (M) Addition Fewer pollinator species and interaction links [53] (Europe) Osmia bicornis Apis mellifera (M) Cage Reduced visitation, niche breadth, nests and brood cells [58] Subalpine (NA) trap-nesting bees None Nectar addition Increased larval mass but not survival [60] Subalpine (NA) Bombus appositus None Nectar + pollen addition Increased queen production [59] Mixed ( ...
Article
Resource competition likely plays an important role in some insect pollinator declines and in shaping effects of environmental change on pollination services. Past research supports that competition for floral resources affects bee foragers, but mostly with observational evidence and rarely linking foraging with population change. An increasing number of studies ask whether resources limit pollinator populations, using field measurements of reproductive success, time series and models. Findings generally support positive effects of floral resources, but also highlight the potential importance of nest site availability and parasitism. In parallel, recent experiments strengthen evidence that competition reduces access to floral resources. Developing common currencies for quantifying floral resources and integrating analyses of multiple limiting factors will further strengthen our understanding of competitive interactions and their effects in the Anthropocene.
... Both honey bees and bumble bees are able to learn similar behaviors and associate them with floral rewards (Stöbbe et al. 2015), but in this case there was a marked difference in behaviors for both experiments on floral choice. These results support conclusions that highlight differences in competitive potential depending on the distribution and quality of resources across the landscape (Herbertsson et al. 2016). ...
Article
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In an enclosed glasshouse with sucrose provisioned artificial flowers, we observed nectar-foraging bumble bees and honey bees under several resource conditions to determine potential for displacement. Different responses were displayed for varying resource treatments. Overall, bumble bees did not show reduced foraging in the presence of honey bees. When resources were reduced, bumble bees did not change their foraging behavior, whereas honey bees responded by decreasing their visitation rate. When a food resource of higher quality was introduced, bumble bee foragers shifted their foraging effort to the high-quality resources, whereas honey bees continued to forage on the lower quality resources they had been foraging on. We discuss these results by considering how the individual strategy of bumble bees compared with the colony-based strategy of honey bees may explain observed differences and highlight the potential advantages of each strategy in the natural environment.
... Densely populated neighborhoods have a very high diversity of flowers ( Lowenstein et al. 2014;Matteson et al. 2013). Again, the high heterogeneity of urban landscapes might promote the diversification and abundance of resources for bees (Williams and Kremen 2007) and mitigate competition ( Herbertsson et al. 2016). Systems in which resources are not limited ( Minckley et al. 2003) or where honey bee density is low (Roubik 1983) can allow cohabitation between wild and honey bees. ...
Article
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Wild bees provide pollination services and are currently declining at the global scale. A potential cause for this decline is competitive interactions with domestic honey bees. Urban beekeeping, a fairly new activity, is rapidly gaining popularity. In contrast with agricultural and natural areas, the extent of competition between honey bees and wild bees in urban areas is unclear. The objectives of this study were to quantify the impact of honey bees, urbanization, and the availability of floral resources on wild bee communities. We hypothesized that honey bees exert negative impacts on wild bees, that floral resources favor wild bee communities and mitigate the negative impacts of competition with honey bees, and that the influence of heat islands, used as a proxy for urbanization, varies between wild bees with their functional traits (nesting behavior). We tested these hypotheses with a data set of 19,077 wild bee specimens collected using colored pan-traps at 25 urban sites in 2012 and 2013. We investigated community and population patterns after accounting for imperfect detection probability. We found no evidence of competition between wild and domesticated bees. Our analyses indicate mixed effects of urban heat islands across species and positive effects of floral resources. We conclude that cities can allow the coexistence of urban beekeeping and wild bees under moderate hive densities. However, it will remain crucial to further investigate the competitive interactions between wild and honey bees to determine the threshold of hive densities beyond which competition could occur.
... Released biological control agents benefit from complex, resource-rich landscapes (Perez-Alvarez et al. 2019); likewise, landscapes with diverse floral resources benefit managed pollinators (Smart et al. 2016). Conversely, releasing biotic IPPM agents into resource-poor landscapes may lead to increased competition between wild and managed pollinators (Herbertsson et al. 2016) or antagonistic interactions between naturally occurring and introduced natural enemies (Perez-Alvarez et al. 2019). ...
Article
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The objective of integrated pest and pollinator management (IPPM) is to co‐manage for pest control and pollination goals. Departing from the well‐established concept of integrated pest management, we include pollinator management in a hierarchical decision support system of management actions. We depict this support system as an IPPM pyramid. Priority is given to proactive measures at the base of the pyramid, which are undertaken through landscape and crop field management of mobile organisms, primarily arthropods. Farther up the pyramid, practices in the form of reactive use of biotic and abiotic inputs should align with basal actions. The goal of IPPM is to minimize trade‐offs, and to maximize co‐benefits and synergies between pest and pollinator management. We contend that IPPM has the potential to contribute to sustainable pest control and crop pollination, as well as provide broader environmental benefits.
... Additionally, their honey provides information on environmental contaminants, such as pesticides, to which bees are exposed when foraging in agricultural systems [4] . Information on foraging preferences is also critical for the parametrization of dynamic honeybee colony models [5] , as well as quantifying their contribution to crop pollination services [6] and/or competitive interaction with wild pollinators [7] . In the UK, beekeeping is rapidly growing with over 29,0 0 0 beekeepers managing around 126,0 0 0 colonies [8] . ...
Article
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Worldwide honeybees (Apis mellifera L.) are one of the most widely kept domesticated animals, supporting domestic and commercial livelihoods though the production of honey and wax, as well as in the delivery of pollination services to crops. Quantifying which plant species are foraged upon by honeybees provides insights into their nutritional status as well as patterns of landscape scale habitat utilization. Here we outline a rapid and reproducible methodology for identifying environmental DNA (eDNA) originating principally from pollen grains suspended within honey. The process is based on a DNA extraction incorporating vacuum filtration prior to universal eukaryotic internal transcribed spacer 2 region (ITS2) amplicon generation, sequencing and identification. To provide a pre-cursor to sequence phylotyping, we outline systems for error-corrected processing amplicon sequence variant abundance tables that removes chimeras. This methodology underpins the new UK National Honey Monitoring Scheme. •We compare the efficacy and speed of centrifugation and filtration systems for removing pollen from honey samples as a precursor to plant DNA barcoding. •We introduce the ‘HONEYPI’ informatics pipeline, an open access resource implemented in python 2.7, to ensure long-term reproducibility during the process of amplicon sequence variant classification.
... Thus, given the variability of both climate, weather and land use in EU, resource availability can vary greatly at smaller and broader geographic scales. Resource availability can also influence competition among bees, in particular between honey bees and bumble bees (Herbertsson et al., 2016). As a result of competition between honey bees and other plantpollinators, high-density beekeeping in natural areas appears to have more serious negative, long-term impacts on native pollinator biodiversity than was previously assumed (Valido et al., 2019). ...
Article
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The European Parliament requested EFSA to develop a holistic risk assessment of multiple stressors in honey bees. To this end, a systems-based approach that is composed of two core components: a monitoring system and a modelling system are put forward with honey bees taken as a showcase. Key developments in the current scientific opinion (including systematic data collection from sentinel beehives and an agent-based simulation) have the potential to substantially contribute to future development of environmental risk assessments of multiple stressors at larger spatial and temporal scales. For the monitoring, sentinel hives would be placed across representative climatic zones and landscapes in the EU and connected to a platform for data storage and analysis. Data on bee health status, chemical residues and the immediate or broader landscape around the hives would be collected in a harmonised and standardised manner, and would be used to inform stakeholders, and the modelling system, ApisRAM, which simulates as accurately as possible a honey bee colony. ApisRAM would be calibrated and continuously updated with incoming monitoring data and emerging scientific knowledge from research. It will be a supportive tool for beekeeping, farming, research, risk assessment and risk management, and it will benefit the wider society. A societal outlook on the proposed approach is included and this was conducted with targeted social science research with 64 beekeepers from eight EU Member States and with members of the EU Bee Partnership. Gaps and opportunities are identified to further implement the approach. Conclusions and recommendations are made on a way forward, both for the application of the approach and its use in a broader context.
... Instead, increasing the density of honeybees could affect wild bees through competition for floral ressource, pathogens spillover or disruption of pollination networks (Geslin et al. 2017;Mallinger et al. 2017). Over the past few years, the body of literature highlighting negative effects of honeybees on wild pollinators has sharply grown (Herbertsson et al. 2016;Magrachet al. 2017;Henry & Rodet 2018;Valido et al. 2019;Hunget al. 2019;Ropars et al. 2019Ropars et al. , 2022Angelella et al. 2021;Renner et al. 2021). For example, as evidenced in Paris, the increase in the number of hives has resulted in exploitative competition for floral resources exerted by honeybees on wild pollinators (Ropars et al. 2019) and same trends have been found in natural reserves or flowering rich habitats in France, Spain and the United States ...
Preprint
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Problem statement: To halt global biodiversity decline, many conservation measures are set up by citizens, companies, or stakeholders. However, even if originally well-intentioned, some of these actions could have direct or indirect negative effects on biodiversity when ecology is not accounted for. The management of bees is a good example of such misplaced conservation practices. We identified three successive errors in the management of bees which can disrupt the focus on real conservation issues: the multiplication of honey bee hives, the installation of insect hotels, the trade of solitary bee cocoons for release into the wild. To help the bees, as well as biodiversity in general, we must consider prioritizing efficient conservation measures which consider more broadly the complexity of ecosystems.
... Further, however, there is also evidence that honey bee colonies can also disrupt the complex relations from which local landscapes emerge. This concern can be broadly grouped into three interconnected tensions that may arise when managed honey bee colonies are introduced into wild ecosystems: (1) possible competition with native bees for nectar and pollen (forage) [105][106][107][108][109][110][111][112][113][114]; (2) increased likelihood and severity of pathogen transmission from managed honeybees to native bee communities [114][115][116][117][118][119]; and, (3) changes in composition of wild plant communities by both providing (honey bee) and deterring (native bee) pollination [68,112,120,121]. ...
Article
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In an era of mass extinction and biodiversity crisis, it is increasingly crucial to cultivate more just and inclusive multispecies futures. As mitigation and adaption efforts are formed in response to these crises, just transitions forward require intentional consideration of the hybrid entanglement of humans, human societies, and wider landscapes. We thus apply a critical hybridity framework to examine the entanglement of the pollinator crisis with the cultural and agricultural practice of hobbyist beekeeping. We draw on ethnographic engagements with Massachusetts beekeepers and find apiculture to be widely understood as a form of environmentalism-including as both a mitigation to and adaptation for the pollinator crisis. Illustrating how power-laden socioecological negotiations shape and reshape regional environments, we then discuss how this narrative relies on the capitalistic and instrumental logics characteristic of Capitalocene environmentalisms. These rationalities, which obscure the hybridity of landscapes, consequently increase the likelihood of problematic unintended consequences. Also present, however, is a deeper engagement with hybrid perspectives, with some beekeepers even offering pathways toward inclusive solutions. We conclude that if more just and biodiverse futures are to be realized, beekeeping communities must foster increasingly hybrid visions of apiculture as situated within socioecological and contested landscapes.
... The degree of competition and thus its direct effects may depend on the availability of resources, with significant impacts occurring only where resources are scarce, such as in the homogeneous agricultural intensification landscapes. However, competition can have less effect when abundant resources are available or when we study heterogeneous landscapes (Thomson, 2006;Herbertsson et al., 2016;Lindström et al., 2016). In addition to the heterogeneity of the landscape, the Apiary Influence Range (AIR) can vary seasonally depending on the amount of the flowering plants in the area (Couvillon et al., 2014). ...
Article
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During the study, honey bee effects on wild bees were tested and hypothesized that smaller distances from beehives will increase competitions between honey bees and wild bees, while greater distances will have a deleterious effect on competition. The impact to species richness and diversity were tested with distances from beehives, considering that this may differ when large and small wild bee species are considered separately. Altogether 158 species and 13164 individuals were collected, from which 72% (9542 individuals) were A. mellifera. High variation in abundances were detected from one year to another, the species turnover by sites were 67% in site A, 66% in site V and 63% in site F. This last one was the site with previous contact with honey bees. Considering distances from beehives, significant decreases in small bee species diversity were detected from one year to another at each distances except site F, 250 m from hives. Change in species diversity and community structure of small bee species are detected from one year to another.
... Sites in our study with this combination of landscape properties are those with many small isolated patches of SNH, which may provide nesting sites for bees, but require them to forage far into the agricultural matrix where floral resources may be scarce. Similar patterns have been reported in Sweden, where competition between honeybees and wild bees and hoverflies increased with crop field size [57], or when the amount of semi-natural grassland in the surrounding landscape was low [58]. By contrast, sites in our study with low habitat diversity but high proximity to SNH, which seem to promote coexistence between managed and wild pollinators, are those with several large patches dominated by a single use such as moorland, rough grassland or even improved grassland, and divided by linear features (e.g. ...
Article
Research into pollinators in managed landscapes has recently combined approaches of pollination ecology and landscape ecology, because key stressors are likely to interact across wide areas. While laboratory and field experiments are valuable for furthering understanding, studies are required to investigate the interacting drivers of pollinator health and diversity across a broader range of landscapes and a wider array of taxa. Here, we use a network of 96 study landscapes in six topographically diverse regions of Britain, to test the combined importance of honeybee density, insecticide loadings, floral resource availability and habitat diversity to pollinator communities. We also explore the interactions between these drivers and the cover and proximity of semi-natural habitat. We found that among our four drivers, only honeybee density was positively related to wild pollinator abundance and diversity, and the positive association between abundance and floral resources depended on insecticide loadings and habitat diversity. By contrast, our exploratory models including habitat composition metrics revealed a complex suite of interactive effects. These results demonstrate that improving pollinator community composition and health is unlikely to be achieved with general resource enhancements only. Rather, local land-use context should be considered in fine-tuning pollinator management and conservation. This article is part of the theme issue ‘Natural processes influencing pollinator health: from chemistry to landscapes’.
... Honey bees are known to affect the distribution of the bumble bees in linear habitats (e.g. Herbertsson et al., 2016), and might have pushed the bumble bees from linear landscape habitats into the flower strips where they had more opportunity of collecting flower rewards. This proposition is partially supported by observations, where abundant short-tongued bumble bee species, such as B. terrestris, only showed weak responses to higher honey bee abundance in phacelia patches, whereas especially long-tongued bumble bee species were displaced by higher honey bee abundance in wild flower patches (Walther-Hellwig et al., 2006). ...
Article
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Wild bee declines in agricultural landscapes have led farmers to supplement crops with honey bees. Simultaneously, environmental subsidy and conservation programmes have incentivized farmers to establish flower strips to support wild and managed pollinators. To find out if flower strips enhance, and competition from honey bees suppresses, wild bees in the landscape and across seasons, we surveyed bumble bee and honey bee abundances in 16 sites in Sweden in summer 2018. The centre of each site (2 km radius) was with or without an annual flower strip, and with or without added honey bee hives. We surveyed bees in each flower strip and in linear habitats in the landscape around each site, such as field edges and road verges. In the following spring, we surveyed bumble bee queen abundance in each site. We show that adding flower strips benefits bumble bee queen abundance the following year, but this effect is diminished if honeybee hives are added. In sites with flower strips, added honey bee hives reduced male bumble bee abundance. Our relatively small flower strip areas bolstered bumble bee population growth across seasons, probably by relieving a resource bottleneck. Adding honey bee hives in combination with flower strips to landscapes with few floral resources should be avoided as it cancelled the positive effect of flower strips.
... In general, mean foraging distances of B. terrestris workers have been reported to be about 200-500 m (Osborne et al., 1999;Redhead et al., 2016) and 2.5 km as a maximum distance (Redhead et al., 2016). Small differences in bumblebee flight distances between study systems may be related to foraging availability at the local and landscape scales (Heinrich, 1979;Redhead et al., 2016). Our study provides empirical data with a good degree of resolution and replication confirming previous findings on the distance at which commercial bumblebees spill over from greenhouses. ...
Article
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Over two million commercial bumblebee colonies are used on an annual basis to pollinate around 20 crop types worldwide. Despite their use, especially with crops grown in greenhouses, there is mounting evidence that many individuals also forage outside of them. Hence, the use of commercial bumblebees poses a risk to wild pollinators, especially to those who share floral resources and pathogens. To date, however, there is little evidence about the impact of commercial bumblebees on pollinator communities in Europe. We surveyed the abundance of commercial Bombus terrestris and the prevalence of four of its parasites in natural areas at increasing distances from vegetable crops in Cabo de Gata-Níjar (Almería, SE Spain), the most extensive greenhouse cultivation area in the world. We also estimated resource niche overlap (i.e., shared plants used) between commercial bumblebees and the native pollinator community. Finally, we explored whether the abundance and diversity of pollinators in natural habitats were influenced by agricultural expansion (i.e., distance to greenhouses) and bumblebee abundance. We found a sharp reduction in commercial bumblebee densities at increasing distances from greenhouses, with most bumblebees (95%) foraging within a radius of less than 200 m from them. However, these commercial bumblebees had high parasite prevalence (41% of individuals infected) of trypanosomatids, microsporidians and neogregarines. Moreover, their diet particularly overlapped with honeybees and large wild bees. Yet, pollinator density and diversity were not related to the distance from greenhouses or to bumblebee abundance. Although our results suggest that commercial bumblebees do not significantly harm wild pollinators, actions like preventing their escape from greenhouses, monitoring their health and optimising their use should be considered so as to minimise future risks.
... Ultimately, the presence of honey bees can reduce the size, biomass and/or reproduction of wild bees (Thomson 2004, Goulson and Sparrow 2009, Elbgami et al. 2014, Torné-Noguera et al. 2016. Competition may be particularly strong when resources are limited (Martins 2004, Thomson 2006, under unfavourable climatic conditions (Thomson 2016) or in homogeneous landscapes (Herbertsson et al. 2016). All of this suggests that massive introductions of honey bees could potentially lead to depauperate wild pollinator communities, with important consequences for natural ecosystems and agricultural productivity (Winfree et al. 2007, Aizen and Harder 2009, Potts et al. 2010b, Breeze et al. 2011, Garibaldi et al. 2013. ...
Article
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Maintaining the diversity of wild bees is a priority for preserving ecosystem function and promoting stability and productivity of agroecosystems. However, wild bee communities face many threats and beekeeping could be one of them, because honey bees may have a strong potential to outcompete wild pollinators when placed at high densities. Yet, we still know little about how beekeeping intensity affects wild bee diversity and their pollinator interactions. Here, we explore how honey bee density relates to wild bee diversity and the structure of their pollination networks in 41 sites on 13 Cycladic Islands (Greece) with similar landscapes but differing in beekeeping intensity. Our large‐scale study shows that increasing honey bee visitation rate had a negative effect on wild bee species richness and abundance, although the latter effect was relatively weak compared to the effect of other landscape variables. Competition for flowering resources (as indicated by a resource sharing index) increased with the abundance of honey bees, but the effect was more moderate for wild bees in family Apidae than for bees in other families, suggesting a stronger niche segregation in Apidae in response to honey bees. Honey bees also influenced the structure of wild bee pollination networks indirectly, through changes in wild bee richness. Low richness of wild bees in sites with high honey bee abundance resulted in wild bee networks with fewer links and lower linkage density. Our results warn against beekeeping intensification in these islands and similar hotspots of bee diversity, and shed light on how benefits to pollination services of introducing honey bees may be counterbalanced by detriments to wild bees and their ecosystem services.
... Similarly, the benefit of managing honeybees may depend on the forage landscape surrounding hives [11], with consequences for the interest of bee keepers to manage hives for honey production. Finally, honeybees and wild pollinators may to a smaller or larger extent share flower resources,, suggesting that they may compete [18,19]. The scope and consequence of competition may depend on their foraging ranges [20], for example whether or not wide-ranging species such as honeybees are able to outcompete less mobile species in simplified landscapes [21]. ...
Article
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Background Recent declines of honeybees and simplifications of wild bee communities, at least partly attributed to changes of agricultural landscapes, have worried both the public and the scientific community. To understand how wild and managed bees respond to landscape structure it is essential to investigate their spatial use of foraging habitats. However, such studies are challenging since the foraging behaviour of bees differs between species and can be highly dynamic. Consequently, the necessary data collection is laborious using conventional methods and there is a need for novel methods that allow for automated and continuous monitoring of bees. In this work, we deployed an entomological lidar in a homogenous white clover seed crop and profiled the activity of honeybees and other ambient insects in relation to a cluster of beehives. Results In total, 566,609 insect observations were recorded by the lidar. The total measured range distribution was separated into three groups, out of which two were centered around the beehives and considered to be honeybees, while the remaining group was considered to be wild insects. The validity of this model in separating honeybees from wild insects was verified by the average wing modulation frequency spectra in the dominating range interval for each group. The temporal variation in measured activity of the assumed honeybee observations was well correlated with honeybee activity indirectly estimated using hive scales as well as directly observed using transect counts. Additional insight regarding the three-dimensional distribution of bees close to the hive was provided by alternating the beam between two heights, revealing a “funnel like” distribution around the beehives, widening with height. Conclusions We demonstrate how lidar can record very high numbers of insects during a short time period. In this work, a spatial model, derived from the detection limit of the lidar and two Gaussian distributions of honeybees centered around their hives was sufficient to reproduce the observations of honeybees and background insects. This methodology can in the future provide valuable new information on how external factors influence pollination services and foraging habitat selection and range of both managed bees and wild pollinators.
... (side 1207). Tilsvarende fant Herbertsson et al. (2016) at honningbier kunne utkonkurrere humler når det gjaldt tilgang til de begrensede ressursene i homogene landskap. ...
Technical Report
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Pollinating insects are in decline over large parts of the world. This global decline is expected to have adverse consequences for biodiversity, ecosystem services and food production in the future. Norway has prepared a pollinator strategy where the goal is, among other things, to ensure viable populations of pollinating insects in order to maintain pollination in food production. This report provides a broad overview of research-based knowledge of factors that affect pollinators and pollination services in different landscapes, as well as an overview of different models for predicting the occurrence of pollinators.
... For example, while managed honeybee populations are in decline in temperate European countries since the 1960s, they are strongly increasing in many southern European countries in the Mediterranean basin (Herrera, 2020). Given that the concentration of large numbers of commercial honeybee colonies in apiaries can negatively affect wild pollinator populations via competition for food Herbertsson et al., 2016;Magrach et al., 2017;Mallinger et al., 2017;Henry and Rodet, 2018;Herrera, 2020 but see Steffan-Dewenter and Tscharntke, 2000) or the dissemination of infectious diseases (Fürst et al., 2014;Graystock et al., 2015;McMahon et al., 2015;Tehel et al., 2016;Alger et al., 2019;Manley et al., 2019;Tehel et al., 2020), managed honeybees could actually exacerbate wild pollinator decline in some regions (Geldmann and González-Varo, 2018). ...
Article
The diversity of endemic honeybee subspecies and ecotypes is at risk in Europe because modern apiculture promotes only a small number of honeybee strains. A crucial step for the conservation of honeybee diversity is the assessment of the status of remaining wild populations and their limiting factors. Here we present a two-year census of native, wild-living honeybees inhabiting power poles in an intensive agricultural landscape in Galicia, NW Spain. The autumn colony densities were at least 0.22 and 0.17 colonies/km² and winter survival rates were 59% and 26% for the years 2019 (N = 29) and 2020 (N = 23), respectively. Both the initial occurrence and the subsequent winter survival of the colonies were positively correlated with increasing proportions of wood- and shrubland in the surroundings in both study years. These observations highlight the importance of semi-natural habitats for the conservation of wild-living honeybees.
Article
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Managed and wild pollinators often cohabit in both managed and natural ecosystems. The western honeybee, Apis mellifera, is the most widespread managed pollinator species. Due to its density and behaviour, it can potentially influence the foraging activity of wild pollinators, but the strength and direction of this effect are often context-dependent. Here, we observed plant-pollinator interactions in 51 grasslands, and we measured functional traits of both plants and pollinators. Using a multi-model inference approach, we explored the effects of honeybee abundance, temperature, plant functional diversity, and trait similarity between wild pollinators and the honeybee on the resource overlap between wild pollinators and the honeybee. Resource overlap decreased with increasing honeybee abundance only in plant communities with high functional diversity, suggesting a potential diet shift of wild pollinators in areas with a high variability of flower morphologies. Moreover, resource overlap increased with increasing trait similarity between wild pollinators and the honeybee. In particular, central-place foragers of family Apidae with proboscis length similar to the honeybee exhibited the highest resource overlap. Our results underline the importance of promoting functional diversity of plant communities to support wild pollinators in areas with a high density of honeybee hives. Moreover, greater attention should be paid to areas where pollinators possess functional traits similar to the honeybee, as they are expected to be more prone to potential competition with this species.
Article
• Declining bumble bees are threatened by habitat loss, pathogens and climate change. Despite policy and management recommendations to create pollinator habitat, the habitat requirements for at‐risk bumble bees remains unclear. Most studies on bumble bee habitat are descriptive, focus on floral resources, occur at one spatial scale, or do not examine at‐risk species. • We provide the first thorough habitat description for two North American bumblebee species (Bombus terricola and Bombus pensylvanicus) at‐risk of extinction. We asked the following questions: (i) What characterises B. terricola and B. pensylvanicus habitat? (ii) Are landscape variables, local variables, or flowering plant species more important determinants of habitat? (iii) do important variables change throughout the season? • Surveys were conducted at 25 sites with a recent occurrence of either B. terricola, B. pensylvanicus, or both species across southern Ontario, Canada. Landscape variables were extracted from a 1‐km buffer around each site. Local variables related to bumble bee resource requirements (floral, nesting and overwintering) and flowering species cover were measured in spring, mid‐summer, and late‐summer. • We found that the proportion of different land cover classes at 1 km was a more important predictor of B. terricola and B. pennsylvanicus presence than local transect based variables such as floral richness or the patchiness of floral cover. We did not find any evidence of important variables changing temporally, but floral resources were consistently important throughout the season. Our results highlight that management of at‐risk pollinator species requires consideration of species‐specific habitat requirements.
Article
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The current knowledge about pollinators in sub‐Saharan Africa is extremely scarce. General pollinator distributions and resource usages are mainly unknown, as are the main pollinators of different crops (Timberlake and Morgan 2018). In early 2011, I travelled to an Afromontane area of Ethiopia, where arabica coffee, Coffea arabica L., has its origin, to survey coffee pollinators. I surveyed 19 coffee sites, most managed with organic practices, across a gradient from state‐owned, shaded semi‐plantation coffee to coffee grown sparsely, more or less wild, in the understory of disturbed natural forests (Fig 1a, b).
Article
Honey bees (Apis mellifera L.) are important agricultural pollinators, and there is increasing demand for forage habitat for managed colonies. However, there is also evidence that pasturing honey bee colonies within natural landscapes may negatively affect wild bees through resource competition. To assess resource competition between managed honey bees and wild bees, we conducted repeated, short‐term deployments of honey bee colonies within Florida forests coinciding with seasonal wildflower bloom, and compared wild bee foraging with and without honey bee colonies present over multiple seasons. We recorded over 2000 bee visits including 196 pairwise bee–plant interactions. Deploying honey bee colonies was associated with a reduction in wild bee foraging rates, and honey bee and wild bee foraging rates were significantly, negatively correlated. Honey bees disproportionately visited resources with high floral density. Honey bee foraging preferences differed significantly from genera with small‐bodied (Lasioglossum, Perdita, Augochlorella), and/or specialist species (Perdita, Andrena), as well as with Megachile, but overlapped with genera including larger‐bodied (Bombus, Habropoda, Osmia, Xylocopa) and/or generalist species (Bombus, Xylocopa, Agapostemon). Deploying honey bee colonies did not significantly affect plant–pollinator network metrics. These results illustrate that short‐term honey bee colony deployment can negatively affect wild bee foraging and that competition may be greater for certain genera, particularly larger‐bodied bees or those with generalist diets though less for smaller‐bodied and/or specialist bees. Our short‐term, low‐density deployment treatments may have precluded significant effects on network metrics and likely underestimate the effects of typical higher density and longer‐term honey bee deployment. Deploying honey bee colonies was associated with a reduction in wild bee foraging rates, and honey bee and wild bee foraging rates were significantly, negatively correlated. Honey bees disproportionately visited resources with high floral density. Honey bee foraging preferences differed significantly from smaller‐bodied and/or specialist bees but overlapped with larger‐bodied and/or generalist bees. Deploying honey bee colonies did not significantly affect plant–pollinator network metrics.
Article
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Prioritizing where to implement management interventions is critical because managers have limited budgets and the effect of habitat enhancement depends on site-specific environmental conditions. Field experiments can identify the conditions where habitat enhancement is most effective, but are typically of limited extent and thus not sufficient for producing spatial predictions that can guide management efforts. We tested if we could produce spatial predictions maps-showing where management interventions to enhance bee habitat would be most successful-by combining spatial predictions of plant community composition (i.e., environmental conditions) obtained from field surveys with a field experiment, in which we quantified the effect of three types of management interventions on bee species richness. Using information from digital maps, we predicted plant species composition within power line clearings across southeast Norway. The intervention type, which involved cutting and removal of the woody vegetation, resulted in the largest increase in bee species richness, but the enhanced bee species richness was limited to clearings with forb-dominated vegetation. Importantly, the estimated effects on bee species richness did not differ between models using the predicted, versus the empirically observed, plant species composition as predictor, making it possible to produce spatial predictions of the increase in bee richness from implementing different management interventions. Synthesis and applications: Combining field surveys with data from field experiments can be used to produce high-resolution maps showing where wild bee habitat enhancement is likely to have the greatest effect. Such maps can inform decisions about where to allocate costly management interventions.
Article
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Understanding the effects of landscape fragmentation on global bumblebee declines requires going beyond estimates of abundance and richness and evaluating changes in community composition and trophic and competitive interactions. We studied the effects of forest fragmentation in a Scandinavian landscape that combines temperate forests and croplands. For that, we evaluated how forest fragmentation features (patch size, isolation and shape complexity, percentage of forest in the surroundings) as well as local flowering communities influenced bumblebee abundance, richness and community composition in 24 forest patches along a fragmentation gradient. In addition, we assessed the effect of fragmentation on bumblebee–plant network specialization (H2′), and potential inter- and intraspecific competition via shared plants. Patch isolation was associated with lower bumblebee abundance, whereas flower density was positively related to both bumblebee abundance and richness. Overall, forest fragmentation reduced the abundance of forest-specialists while increasing the abundance of open-habitat species. Patches with complex shapes and few flowers showed more generalized bumblebee–plant networks (i.e., fewer specific interactions). Patch shape complexity and the percentage of forest also modified inter- and intraspecific competitive interactions, with habitat generalists outcompeting forest specialists in fragmented areas. Understanding these mechanisms is necessary to anticipate to the impact of forest fragmentation on bumblebee decline.
Article
Spatial aspects of connectivity have received considerable attention from ecologists and conservationists, yet temporal connectivity – the periodic linking of habitats – plays an equally important, but largely overlooked role. Different biological and biophysical attributes of ecosystems underpin temporal connectivity, but here we focus on resource continuity, the uninterrupted availability of foraging sites. We test the response of pollinators to resource continuity at community, population and individual levels using a novel natural experiment consisting of farms with either single or sequential cropping systems. We found significant effects at the population level; colony density of an important crop pollinator (Bombus impatiens L.) was greater when crop floral resources were continuously available. However, we did not find significant effects at the community or individual level; wild bee abundance, diversity and body size did not respond to resource continuity. Raspberry farms with greater early season resources provided by blueberry had greater bumble bee populations, suggesting beneficial effects on resource availability due to crop diversity. Better understanding the impact of resource continuity via crop diversity on broader patterns of biodiversity is essential for the co‐management of biodiversity and ecosystem services.
Article
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A pesar de que España es uno de los países con mayor diversidad de polinizadores silvestres y, que de su conservación depende el futuro de nuestros cultivos y por tanto de nuestra alimentación, lo cierto es que hoy día seguimos sin conocer el estado de conservación de gran parte de esta fauna, una demanda histórica de la sociedad cien- tífica que sigue sin cubrirse en la actualidad. Bajo esta premisa nace este decálogo, fruto de la colaboración de un conjunto de científicos/as especialistas en la materia, quienes han realizado una revisión profunda de la literatura científica sobre el declive de insectos polinizadores desde principios del siglo XX hasta hoy día, que puede consultarse en el monográfico Pérdida de poli- nizadores publicado por la Revista Ecosistemas de la Asociación Española de Ecología Terrestre (AEET). El propósito de este decálogo es recoger una serie de aspectos fundamentales sobre el declive en la península Ibérica de los polinizadores silvestres, los más sensibles a los cambios de los últimos años, para abrir el debate sobre una serie de medidas ur- gentes para su conservación. 1. Conservar y restaurar el paisaje 2. Aumentar la disponibilidad de flores en el medio silvestre, áreas agrícolas y ciudades 3. Maximizar la disponibilidad de recursos de nidificación y oviposición 4. Reducir el uso de plaguicidas 5. Fomentar una agricultura sostenible 6. Realizar acciones de sensibilización y educación sobre los beneficios que los polinizadores silvestres proporcionan al ser humano y al medio ambiente 7. Legislar la protección de las especies más sensibles 8. Potenciar la coordinación de los trabajos de protección y restauración 9. Mejorar la educación ambiental impartida a los agricultores/as 10. Impulsar la investigación y conocimiento sobre los polinizadores silvestres
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The European honeybee Apis mellifera is a highly successful, abundant species and has been introduced into habitats across the globe. As a supergeneralist species, the European honeybee has the potential to disrupt pollination networks, especially in Australia, whose flora and fauna have co-evolved for millions of years. The role of honeybees in pollination networks in Australia has been little explored and has never been characterised in urban areas, which may favour this exotic species due to the proliferation of similarly exotic plant species which this hyper-generalist can utilise, unlike many native bee taxa. Here, we use a bipartite network approach to compare the roles, in terms of species-level properties, of honeybees with native bee taxa in bee-flower (‘pollination’) networks in an urbanised biodiversity hotspot. We also assessed whether the abundance of honeybees influences overall network structure. Pollination networks were created from surveys across seven residential gardens and seven urban native vegetation remnants conducted monthly during the spring-summer period over two years. There were consistent differences in species-level properties between bee taxa, with honeybees often differing from all other native bees. Honeybees had significant impacts on network properties, being associated with higher nestedness, extinction slopes of plants, functional complementarity and niche overlap (year two), as well as lower weighted connectance and generalisation. These associations all are indicative that competition is occurring between the introduced honeybee and the native bee taxa in bee-flower networks. In conclusion, the introduced honeybee occupies a dominant, distinct position in bee-flower networks in urban habitats in the southwest Western Australian biodiversity hotspot and has a major, potentially disruptive, influence on plant-pollinator network properties in these areas.
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The European Parliament requested EFSA to develop a holistic risk assessment of multiple stressors in honey bees. To this end, a systems-based approach that is composed of two core components: a monitoring system and a modelling system is put forward with honey bees taken as a showcase. Key developments in the current scientific opinion (including systematic data collection from sentinel bee hives and an agent-based simulation) have the potential to substantially contribute to future development of environmental risk assessments of multiple stressors at larger spatial and temporal scales. For the monitoring, sentinel hives would be placed across representative climatic zones and landscapes in the EU and connected to a platform for data storage and analysis. Data on bee health status, chemical residues and the immediate or broader landscape around the hives would be collected in a harmonised and standardised manner, and would be used to inform stakeholders, and the modelling system, ApisRAM, which simulates as accurately as possible a honey bee colony. ApisRAM would be calibrated and continuously updated with incoming monitoring data and emerging scientific knowledge from research. It will be a supportive tool for beekeeping, farming, research, risk assessment and risk management, and it will benefit the wider society. A societal outlook on the proposed approach is included and this was conducted with targeted social science research with 64 beekeepers from eight EU Member States and with members of the EU Bee Partnership. Gaps and opportunities are identified to further implement the approach. Conclusions and recommendations are made on a way forward, both for the application of the approach and its use in a broader context.
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Pollinator refuges such as wildflower strips are planted on farms with the goals of mitigating wild pollinator declines and promoting crop pollination services. It is unclear, however, whether or how these goals are impacted by managed honey bee (Apis mellifera L.) hives on farms. We examined how wildflower strips and honey bee hives and/or their interaction influence wild bee communities and the fruit count of two pollinator-dependent crops across 21 farms in the Mid-Atlantic U.S. Although wild bee species richness increased with bloom density within wildflower strips, populations did not differ significantly between farms with and without them whereas fruit counts in both crops increased on farms with wildflower strips during one of 2 years. By contrast, wild bee abundance decreased by 48%, species richness by 20%, and strawberry fruit count by 18% across all farm with honey bee hives regardless of wildflower strip presence, and winter squash fruit count was consistently lower on farms with wildflower strips with hives as well. This work demonstrates that honey bee hives could detrimentally affect fruit count and wild bee populations on farms, and that benefits conferred by wildflower strips might not offset these negative impacts. Keeping honey bee hives on farms with wildflower strips could reduce conservation and pollination services.
Technical Report
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Vilde bestøvende insekter er generelt truede. De vilde bier, dagsommerfugle og svirrefluer, som denne rapport har fokus på, stiller imidlertid forskellige krav til levestedet gennem forskellige dele af livscyklus. I rapporten er levestedskravene eller habitatressourcerne, som de også kaldes, grundigt beskrevet for humlebier, enlige bier, dagsommerfugle og svirrefluer. For at modvirke tilbagegangen af insekterne kan iværksættes forskellige virkemidler. Rapporten gennemgår relevante eksisterende og mulige fremtidige virkemidler i forhold til at tilgodese insekternes levestedskrav og giver desuden anbefalinger til, hvordan det enkelte virkemiddel kan ændres for i større grad at understøtte vilde bestøvende insekter. I modsætning til tidligere vurderinger af virkemidler i forhold til vilde bestøvende insekter vurderer denne rapport ikke blot, i hvilket omfang virkemidlet bidrager med egnede fødeemner, men også hvorvidt øvrige levestedskrav er opfyldt.
Technical Report
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This report examines the extent to which pollinator conservation measures are currently integrated into the EU Common Agricultural Policy (CAP) and how managing authorities and farmers can increase their effectiveness. This addresses a key objective of the 2018 EU Pollinators initiative which aims to halt the decline of pollinators in the EU.
Chapter
The main aim of pollinator integrated pest management technology (PIPMT) is to integrate pollinator services in pest management strategies for enhancing productivity. Deviating from the idea of integrated pest management, we incorporate pollinators in an action process of pest management in hierarchy. We portray this new champion approach as a PIPMT hierarchy. Preference is given to enterprising actions at the foundation of a pyramid model, which are set in motion through farming, landscape, pest management, and crop pollinators. In addition to the pyramid model, procedures in the shape of responsive manipulation of biotic and abiotic factors should line up with fundamental activities. The objective of PIPMT is to keep down trade-offs, and to enhance co-benefits and collaboration between bee pollinators and pest control strategies. We assert that PIPMT has the great potential in a sustainable crop pest and bee pollination management system, as well as beneficial for the bio-ecosystem.
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The cultivation of mass-flowering crops (MFC) can promote pollinators by providing floral resources. However, there is missing knowledge about the effect of MFC cultivation history on bees and their pollination services in agricultural landscapes. We investigated how bee densities in oilseed rape (Brassica napus L.) (OSR) fields were affected by past (cultivation area of the preceding three years) and current MFC area coverages in the surrounding landscape. Moreover, we analyzed how insect pollination, its possible interaction with the plants` pod numbers and MFC covers influence yield components of individual OSR plants and calculated yields (t/ha). To test this, we conducted pollinator surveys and a pollinator exclusion experiment in one oilseed rape field in 17 agricultural landscapes in Germany. We found that wild bee densities were positively affected by past MFC covers and negatively impacted by current OSR covers, indicating enhanced pollinator populations due to previous MFC cultivation and contemporary pollinator dilution. In contrast, honeybees showed opposite responses to past and present MFC cultivation. Furthermore, seed weight per plant of open pollinated plants was positively correlated with past MFC covers. Pollinator exclusion decreased the seed number per pod and increased thousand-seed weight, while yields were unaffected. Pod number interacted with insect pollination in shaping yields, such that pollinator exclusion led to a steeper increase of yield with higher pod numbers. Insect pollination compensated for low pod numbers by increasing the plants` seed number per pod and ultimately yields. Our findings demonstrate a beneficial effect of high MFC covers in the past on bee densities and potentially yield components in the current year. Our study highlights the need for further research on how past and present landscape composition in terms of MFC cultivation interactively affect pollinator communities and their pollination services in agricultural landscapes.
Article
Over the past two decades, the cultivated area of oilseed rape (Brassica napus L. or OSR), a mass-flowering crop, has markedly increased in Europe in response to bioenergy demands. As well as representing a major shift in floral composition across the landscape, mass-flowering OSR may alter pollination services to other simultaneously blooming crops, either decreasing pollination via competition for pollinators or facilitating it via pollinator spill-over. Apple (Malus domestica Borkh.) is an economically important, obligately insect-pollinated fruit crop that co-flowers with OSR. Using twelve independent apple orchards varying in the percentage of OSR in the surrounding landscape, we investigated the effect of OSR on pollinators and pollination of co-blooming apple. We collected bees with pan traps and quantified flower visitors during transect walks in both crops and we experimentally measured pollination service provision to apple as fruit and seed set. We confirm that apples are highly dependent on animal pollination and report pollination limitation in our apple orchards. Honey bees were the numerically dominant visitors of apple flowers observed during transect walks. Though their numbers dropped with an increasing percentage of OSR in the landscape, the number of bumble bees visiting apple flowers remained stable and those of other wild bees rose. The pan trapped Shannon diversity of bees remained constant. We could not detect an effect of OSR in the landscape on apple fruit set or seed set, both of which remained stable. Local wild bee populations might compensate for the loss of honey bees in the provision of pollination services in apple, providing especially effective pollination. Our results underscore not only the dominant role of bees in apple pollination but also the importance of wild bee conservation for providing pollination insurance and stability of apple crop yields under changing agricultural policies and cropping practices.
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A recurrent concern in nature conservation is the potential competition for forage plants between wild bees and managed honey bees. Specifically, that the highly sophisticated system of recruitment and large perennial colonies of honey bees quickly exhaust forage resources leading to the local extirpation of wild bees. However, different species of bees show different preferences for forage plants. We here summarize known forage plants for honey bees and wild bee species at national scale in Denmark. Our focus is on floral resources shared by honey bees and wild bees, with an emphasis on both threatened wild bee species and foraging specialist species. Across all 292 known bee species from Den-mark, a total of 410 plant genera were recorded as forage plants. These included 294 plant genera visited by honey bees and 292 plant genera visited by different species of wild bees. Honey bees and wild bees share 176 plant genera in Denmark. Comparing the pairwise niche overlap for individual bee species, no significant relationship was found between their overlap and forage specialization or conservation status. Network analysis of the bee-plant interactions placed honey bees aside from most other bee species, specifically the module containing the honey bee had fewer links to any other modules, while the remaining modules were more highly interconnected. Despite the lack of predictive relationship from the pair-wise niche overlap, data for individual species could be summarized. Consequently, we have identified a set of operational parameters that, based on a high foraging overlap (>70%) and unfavorable conservation status (Vulnerable+Endangered+Critically Endangered), can guide PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.
Thesis
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La crise de la biodiversité affecte le fonctionnement de tous les écosystèmes, notamment agricoles, via une perte des services écosystémiques. Favoriser les populations d’organismes à l’origine de ces services via des stratégies de diversification végétale est un levier prometteur pour maintenir une production agricole élevée ainsi que la santé des écosystèmes, mais les résultats obtenus sont variables et peu expliqués. L’objectif de cette thèse est de comprendre comment l’augmentation de la diversité cultivée impacte la structure et le fonctionnement des communautés de pollinisateurs et d’ennemis naturels en considérant leurs interactions. Nos résultats montrent que la diversification des ressources modifie la composition des communautés, pouvant mener à des interactions négatives. Dans les réseaux trophiques puceron – parasitoïde – hyperparasitoïde, la diversification semble avoir augmenté l’hyperparasitisme et la compétition entre les parasitoïdes primaires, ce qui expliquerait un contrôle des pucerons limité. L’utilisation massive des fleurs cultivées par les abeilles domestiques semble limiter l’utilisation de cette ressource par les pollinisateurs sauvages. De plus, nous avons observé une diminution du service de régulation des pucerons par les parasitoïdes en réponse à une forte abondance de pollinisateurs, signalant pour la première fois de possibles interactions négatives entre ces deux groupes. Optimiser plusieurs services écosystémiques simultanément demande de repenser les paysages agricoles en considérant l’utilisation des ressources de chaque groupe d’organismes à différentes échelles spatio-temporelles ainsi que les interactions au sein et entre ces groupes.
Article
The decline of pollinators is a widespread problem in today's agriculture, affecting the yield of many crops. Improved pollination management is therefore essential, and honey bee colonies are often used to improve pollination levels. In this work, we applied a spatially explicit agent-based model for the simulation of crop pollination by honey bees under different management scenarios and landscape configurations. The model includes 1) a representation of honey bee social dynamics; 2) an explicit representation of resource dynamics; 3) a probabilistic approach to the foraging site search process; and 4) a mechanism of competition for limited resources. We selected 60 sample units from the rural landscape of the Chilean region with the largest apple-growing area and evaluated the effectiveness of different pollination strategies in terms of number of visits and number of pollinated flowers per hectare of apple crops. Finally, we analyzed how the effects of these practices depended on the structure of adjacent landscapes. Higher colony density per hectare in the focal crop increased the number of honey bee visits to apple inflorescences; however, the effects were nonlinear for rates of pollinated flowers, suggesting that there is an optimum beyond which a greater number of honey bees does not signify increased levels of crop pollination. Furthermore, high relative proportions of mass flowering crops and natural habitats in the landscape led to a decrease in honey bee densities in apple fields in landscapes with high relative cover of apple orchards (dilution effect). Our results indicate that for optimal crop pollination, strategies for management of pollinator species should consider the modulating effects of the surrounding landscape on pollination effectiveness. This model could thus be a useful tool to help farmers, beekeepers, and policy-makers plan the provision of pollination services, while also promoting the biodiversity and sustainability of agroecosystems.
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Insect pollination, despite its potential to contribute substantially to crop production, is not an integrated part of agronomic planning. A major reason for this are knowledge gaps in the contribution of pollinators to yield, which partly result from difficulties in determining area-based estimates of yield effects from insect pollination under field conditions. We have experimentally manipulated honey bee Apis mellifera densities at 43 oilseed rape Brassica napus fields over 2 years in Scandinavia. Honey bee hives were placed in 22 fields; an additional 21 fields without large apiaries in the surrounding landscape were selected as controls. Depending on the pollination system in the parental generation, the B. napus cultivars in the crop fields are classified as either open-pollinated or first-generation hybrids, with both types being open-pollinated in the generation of plants cultivated in the fields. Three cultivars of each type were grown. We measured the activity of flower-visiting insects during flowering and estimated yields by harvesting with small combine harvesters. The addition of honey bee hives to the fields dramatically increased abundance of flower-visiting honey bees in those fields. Honey bees affected yield, but the effect depended on cultivar type (p = 0.04). Post-hoc analysis revealed that open-pollinated cultivars, but not hybrid cultivars, had 11% higher yields in fields with added honey bees than those grown in the control fields (p = 0.07). To our knowledge, this is the first whole-field study in replicated landscapes to assess the benefit of insect pollination in oilseed rape. Our results demonstrate that honey bees have the potential to increase oilseed rape yields, thereby emphasizing the importance of pollinator management for optimal cultivation of oilseed rape.
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Intensive beekeeping to mitigate crop pollination deficits and habitat loss may cause interspecific competition between bees. Studies show negative correlations between flower visitation of honey bees (Apis mellifera) and wild bees, but effects on the reproduction of wild bees were not proven. Likely reasons are that honey bees can hardly be excluded from controls and wild bee nests are generally difficult to detect in field experiments. The goal of this study was to investigate whether red mason bees (Osmia bicornis) compete with honey bees in cages in order to compare the reproduction of red mason bees under different honey bee densities. Three treatments were applied, each replicated in four cages of 18 m³ with 38 red mason bees in all treatments and 0, 100, and 300 honey bees per treatment with 10–20% being foragers. Within the cages, the flower visitation and interspecific displacements from flowers were observed. Niche breadths and resource overlaps of both bee species were calculated, and the reproduction of red mason bees was measured. Red mason bees visited fewer flowers when honey bees were present. Niche breadth of red mason bees decreased with increasing honey bee density while resource overlaps remained constant. The reproduction of red mason bees decreased in cages with honey bees. In conclusion, our experimental results show that in small and isolated flower patches, wild bees can temporarily suffer from competition with honey bees. Further research should aim to test for competition on small and isolated flower patches in real landscapes.
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Agricultural intensification has resulted in large-scale loss of bee pollinators, but while some species have been negatively affected others seem to endure changed conditions. It has been suggested that certain morphological, ecological and life-history traits make some species more vulnerable to landscape changes. Information on which traits make species vulnerable and why may aid conservation of declining species. We performed a comprehensive analysis of how multiple traits related to diet breadth, movement and nesting habits moderate vulnerability of bumble bees to landscape simplification. We surveyed bumble bees in flower-rich non-crop habitats in either complex landscapes (with small crop fields bordered by non-crop habitats), or simple landscapes (with larger fields and therefore less non-crop habitats). We analysed if landscape type interacted with colony size, queen emergence date, colony life-cycle length, nesting habitat, thorax width, proboscis length or variability in thorax and proboscis, to explain bumble bee abundances. Workers and males of species with above-ground nests, small sized colonies and long colony cycle were relatively less abundant in simple compared to in complex landscapes. Simple landscapes hosted fewer males of late emerging species and species with highly variable proboscis length. This suggests that both nesting habitat and spatio-temporal availability of food resources act as ecological filters for bumble bees. Colony size correlated with nesting habitat and queen emergence when correcting for phylogenetic correlations, suggesting that landscape simplification acts through effects on combinations of traits. Our results have consequences for conservation by suggesting that declining bumble bee species can be supported by providing adequate nesting habitats and preferred plant species throughout the season and within short distance from nesting habitats, to allow utilisation also by species having colonies with few workers.
Technical Report
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Description Fit linear and generalized linear mixed-effects models. The models and their components are represented using S4 classes and methods. The core computational algorithms are implemented using the 'Eigen' C++ library for numerical linear algebra and 'RcppEigen' ``glue''.
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Multiple bee species may forage simultaneously at a common resource. Physical encounters among these bees may modify their subsequent foraging behavior and shape pollinator distribution and resource utilization in a plant community. We observed physical encounters between honey bees, Apis mellifera, and bumble bees, Bombus impatiens, visiting artificial plants in a controlled foraging arena. Both species were more likely to leave the plant following an encounter with another bee, but differed in their responses to intra- and inter-specific encounters. A. mellifera responded similarly to an encounter with either species. However, most B. impatiens that encountered A. mellifera discontinued foraging at the observed plant, but exhibited only a slight decrease in foraging following an intraspecific encounter. Interactions between bees that elicit changes in foraging behavior may have important implications for the pollination of wild and managed plants.
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European honey bees used for commercial honey production represent a potential source of competition for floral resources with native nectar and pollen feeding insects. This study reports the results of an experiment run over two years on the impact of commercial honey bees on the fecundity of a solitary native bee, Hylaeus alcyoneus. Registered apiary sites were used as treatment sites (with honey bees) while control sites (without honey bees) were interspersed between. The fecundity of H. alcyoneus was measured using trap nests. We compared the number of nests produced, number of eggs per nest and emerging progeny mass of H. alcyoneus in sites with and without commercial bee hives. The number of nests produced by H. alcyoneus was 23% less (Wilcoxon’s T) at treatment sites than control sites. Analysis of individual measurement intervals using ANOVA was compromised by a general lack of power. This result highlights that even though honey bees have been present in certain areas for many years, competition with native bees may still be occurring.
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Abstract Interspecific competition for a limited resource can result in the reduction of survival, growth and/or reproduction in one of the species involved. The introduced honey bee (Apis mellifera Linnaeus) is an example of a species that can compete with native bees for floral resources. Often, research into honey bee/native bee competition has focused on floral resource overlap, visitation rates or resource harvesting, and any negative interaction has been interpreted as a negative impact. Although this research can be valuable in indicating the potential for competition between honey bees and native bees, to determine if the long-term survival of a native bee species is threatened, fecundity, survival or population density needs to be assessed. The present review evaluates research that has investigated all these measurements of honey bee/native bee competition and finds that many studies have problems with sample size, confounding factors or data interpretation. Guidelines for future research include increasing replication and using long-term studies to investigate the impact of both commercial and feral honey bees.
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Summary 1. Plant-pollinator interactions are crucial for the reproduction of most angiosperms. When faced with perturbations, plant-pollinator networks might be robust mainly due to the presence of highly generalist species. Perturbations can, in turn, affect how pollinators exploit their food sources and therefore their degree of generalization. 2. In particular, generalization of pollinators might vary with forager density. At high densities floral resources available in plant communities would be more rapidly depleted than at low densities. According to optimal foraging theory (OFT), this decrease in resources should lead to an increase in diet breadth. 3. We investigated the impact of pollinator density on diet breadth of Bombus terrestris . We recorded the individual foraging behaviour of bumblebees from eight colonies. They foraged in presence of either one or several conspecifics on experimental plant communities composed of five plant species. Diet breadth was calculated as the number of plant species visited, as well as by the Levins index. We analyzed the effect of forager density on diet breadth at both the individual and the colony levels. 4. We found that forager density affected degree of generalization at individual and colony levels. A more competitive environment increased individual generalization, as predicted by OFT, and decreased the variability in generalization across colonies. Moreover, we found that bumblebee size was positively related to the amplitude of diet breadth change. 5. Synthesis . Our study sheds light on an additional level of complexity of plant-pollinator systems, showing that pollinator diet breadth is a flexible trait which results from behavioural adaptation to resource availability. More generally, changes in foraging insects' diet via competition for resources are likely to ensue from anthropogenic ecosystem disturbance and to impact upon the functioning of plant-pollinator networks.
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1. Waggle dances of honey-bees (Apis mellifera L.) were decoded to determine where and how far the bees foraged during the blooming of heather (Calluna vulgaris L.) in August 1996 using a hive located in Sheffield, UK, east of the heather moors. The median distance foraged was 6·1 km, and the mean 5·5 km. Only 10% of the bees foraged within 0·5 km of the hive whereas 50% went more than 6 km, 25% more than 7·5 km and 10% more than 9·5 km from the hive.2. These results are in sharp contrast with previous studies in which foraging distances were much closer to the hive. In May 1997 the mean foraging distance was 1 km, showing that long-range dancing is not the rule in Sheffield.3. The observed foraging distances described in this study may not be exceptional in a patchy environment where differences in patch size and patch quality are large. When travel distances to patches are large, distant patches can probably be utilized only by individuals that live in groups and recruit foragers to the patches found. Only then are the benefits of scouting for distant patches high enough to enable the exploitation of these patches.
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Evidence for interspecific competition between honey bees and wild bees was studied on 15 calcareous grasslands with respect to: (1) foraging radius of honey bees, (2) overlap in resource use, and (3) possible honey bee effects on species richness and abundance of flower-visiting, ground-nesting and trap-nesting wild bees. The grasslands greatly differed in the number of honey bee colonies within a radius of 2 km and were surrounded by agricultural habitats. The number of flower-visiting honey bees on both potted mustard plants and small grassland patches declined with increasing distance from the nearest apiary and was almost zero at a distance of 1.5–2.0 km. Wild bees were observed visiting 57 plant species, whereas honey bees visited only 24 plant species. Percentage resource overlap between honey bees and wild bees was 45.5%, and Hurlbert’s index of niche overlap was 3.1. In total, 1849 wild bees from 98 species were recorded on the calcareous grasslands. Neither species richness nor abundance of wild bees were negatively correlated with the density of honey bee colonies (within a radius of 2 km) or the density of flower-visiting honey bees per site. Abundance of flower- visiting wild bees was correlated only with the percentage cover of flowering plants. In 240 trap nests, 1292 bee nests with 6066 brood cells were found. Neither the number of bee species nor the number of brood cells per grassland was significantly correlated with the density of honey bees. Significant correlations were found only between the number of brood cells and the percentage cover of shrubs. The number of nest entrances of ground-nesting bees per square metre was not correlated with the density of honey bees but was negatively correlated with the cover of vegetation. Interspecific competition by honey bees for food resources was not shown to be a significant factor determining abundance and species richness of wild bees.
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In subtropical dry forest (Chaco Serrano) of Tucuman province, northwestern Argentina, we assessed responses of the flower-visitor assemblage to habitat fragmentation by monitoring insect visits to two spring-flowering tree species and by sampling insects with yellow pan traps. Each of four study sites contained a tract of continuous forest, one large (>2.2 ha) forest fragment, and one small (90% of observed flower visits to both plant species. The honey bee alone made 82% of all visits to the early-flowering tree species P. nigra and 44% to the later flowering C. australe. Frequency and taxon richness of native flower-visitors at both plant species declined with decreasing forest-fragment size, but frequency of honey bee visits tended to increase in complementary fashion, such that the total frequency of insect visits to flowers of either plant species varied little with fragment size. Frequencies of visits by honey bees and those by native insects were also negatively correlated across individual trees. In both plants, visits by native insects were most consistent (varied the least among plants or over time) in large forest tracts, whereas honey bee visits to C. australe were most consistent in small fragments. In pan trap samples the relative frequency of honey bees increased with decreasing fragment size. Native flower-visitors sampled by pan traps increased in numbers and taxon richness both with increasing patch size and as spring progressed. Thus, fragmentation of the Chaco Serrano appears to (a) affect native flower-visitors adversely and to (b) facilitate honey bees' access to floral resources. It is not clear that these two effects are directly related to each other, however.
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The increasing numbers of endangered wild bee species highlights the need for quantifying potential adverse effects of foraging honeybees. We analysed the response of bumblebees at genus and species level to experimentally increased honeybee density. The study was carried out on a Phacelia tanacetifolia field and adjacent patches of wild plants located in an agricultural landscape. Addition of one or ten A. m. ligustica colonies substantially increased total honeybee density not only on Phacelia but also on neighbouring patches of wild plants. The response of bumblebees (Bombus spp.) differed among species. Only minor spatial changes in the abundance of the short-tongued B. terrestris-group were observed on Phacelia. At wild plant patches, the B. lapidarius-group and the longer tongued bumblebee species (B. muscorum, B. sylvarum, B. pascuorum) responded with a shift between plant species. Limitations of competition avoidance in flower-impoverished landscapes are discussed.
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Honeybees communicate the distance and location of resource patches by bee dances, but this spatial information has rarely been used to study their foraging ecology. We analysed, for the first time to the best of the authors' knowledge, foraging distances and dance activities of honeybees in relation to landscape structure, season and colony using a replicated experimental approach on a landscape scale. We compared three structurally simple landscapes characterized by a high proportion of arable land and large patches, with three complex landscapes with a high proportion of semi-natural perennial habitats and low mean patch size. Four observation hives were placed in the centre of the landscapes and switched at regular intervals between the six landscapes from the beginning of May to the end of July. A total of 1137 bee dances were observed and decoded. Overall mean foraging distance was 1526.1 +/- 37.2 m, the median 1181.5 m and range 62.1-10037.1 m. Mean foraging distances of all bees and foraging distances of nectar-collecting bees did not significantly differ between simple and complex landscapes, but varied between month and colonies. Foraging distances of pollen-collecting bees were significantly larger in simple (1743 +/- 95.6 m) than in complex landscapes (1543.4 +/- 71 m) and highest in June when resources were scarce. Dancing activity, i.e. the number of observed bee dances per unit time, was significantly higher in complex than in simple landscapes, presumably because of larger spatial and temporal variability of resource patches in complex landscapes. The results facilitate an understanding of how human landscape modification may change the evolutionary significance of bee dances and ecological interactions, such as pollination and competition between honeybees and other bee species.
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Coexistence in bumblebee communities has largely been investigated at local spatial scales. However, local resource partitioning does not fully explain the species diversity of bumblebee communities. Theoretical studies provide new evidence that partitioning of space can promote species coexistence, when species interact with their environment at different spatial scales. If bumblebee species possess specific foraging ranges, different spatial resource utilisation patterns might operate as an additional mechanism of coexistence in bumblebee communities. We investigated the effects of the landscape-wide availability of different resources (mass flowering crops and semi-natural habitats) on the local densities of four bumblebee species at 12 spatial scales (landscape sectors with 250-3,000 m radius) to indirectly identify the spatial scales at which the bumblebees perceive their environment. The densities of all bumblebee species were enhanced in landscapes with high proportions of mass flowering crops (mainly oilseed rape). We found the strongest effects for Bombus terrestris agg. and Bombus lapidarius at large spatial scales, implying foraging distances of 3,000 and 2,750 m, respectively. The densities of Bombus pascuorum were most strongly influenced at a medium spatial scale (1,000 m), and of Bombus pratorum (with marginal significance) at a small spatial scale (250 m). The estimated foraging ranges tended to be related to body and colony sizes, indicating that larger species travel over larger distances than smaller species, presumably enabling them to build up larger colonies through a better exploitation of food resources. We conclude that coexistence in bumblebee communities could potentially be mediated by species-specific differences in the spatial resource utilisation patterns, which should be considered in conservation schemes.
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Bees are the most important pollinator taxon; therefore, understanding the scale at which they forage has important ecological implications and conservation applications. The foraging ranges for most bee species are unknown. Foraging distance information is critical for understanding the scale at which bee populations respond to the landscape, assessing the role of bee pollinators in affecting plant population structure, planning conservation strategies for plants, and designing bee habitat refugia that maintain pollination function for wild and crop plants. We used data from 96 records of 62 bee species to determine whether body size predicts foraging distance. We regressed maximum and typical foraging distances on body size and found highly significant and explanatory nonlinear relationships. We used a second data set to: (1) compare observed reports of foraging distance to the distances predicted by our regression equations and (2) assess the biases inherent to the different techniques that have been used to assess foraging distance. The equations we present can be used to predict foraging distances for many bee species, based on a simple measurement of body size.
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This paper describes the implementation in R of a method for tabular or graphical display of terms in a complex generalised linear model. By complex, I mean a model that contains terms related by marginality or hierarchy, such as polynomial terms, or main effects and interactions. I call these tables or graphs effect displays. Effect displays are constructed by identifying high-order terms in a generalised linear model. Fitted values under the model are computed for each such term. The lower-order "relatives" of a high-order term (e.g., main effects marginal to an interaction) are absorbed into the term, allowing the predictors appearing in the high-order term to range over their values. The values of other predictors are fixed at typical values: for example, a covariate could be fixed at its mean or median, a factor at its proportional distribution in the data, or to equal proportions in its several levels. Variations of effect displays are also described, including representation of terms higher-order to any appearing in the model.
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Previous studies of introduced honey bees foraging at Agave schottii flowers suggest that Apis mellifera preferentially exploits the most productive patches of flowers and thereby reduces the standing crop of available nectar and the utilization of these sites by native bees. Results of experiments undertaken to evaluate this hypothesis are given and discussed using Apis, Bombus and Xylocopa. -Authors
Article
The resource utilization by nine species of bumblebees in a subarctic community was studied by analysing the distribution of the depths of the corolla tubes of the visited flower species. When measured in this way, the food niches of the bumblebee species showed a wide overlap. Species with a long proboscis could use flowers with short corolla tubes for feeding, whereas the reverse was rare. We postulate that foraging efficiency is maximal when the proboscis length of a species corresponds to the corolla tube depth of the flower visited. An analysis of published data supports this hypothesis. The paucity of plant species with deep corolla tubes thus explains the small number and low abundance of bumblebee species with long proboscis. The continuously changing pattern of corolla tube depths due to the seasonal succession of plant species facilitates the coexistence of many bumblebee species in a community in spite of small differences in proboscis length. /// Исследовали утилизацию пищевых ресурсов 9-ю видами шмелей в субарктическом сообществе методом анализа глубины трубочек венчиков посещаемых цветов. При таких определениях пищевые ниши разных видов шмелей широко перекрываются. Виды с длинным хоботком могут использовать для питания цветы с короткой трубочкой венчика, обратное соотношение наблюдалось редко. Мы полагаем, что эффективность фуражировки максимальна, если длина хоботка соответсвует длине трубочки венчика посещаемого цветка. Анализ опубликованных данных подтверждает эту гипотезу. Малое количество видов растений с длинными трубочками венчика цветка обьясняет таким образом, и малое число вкдов и низкую уисленность шмелей с длинными хоботком. Посторнные колебания длины трубочек венчиков цветков в результате сезонной сукцессии видов растений облегчает сосуществование многих видов шмелей в чообществе, несмотря на незначительные различия в длине хоботка.
Article
1. The feeding plants of queens and workers of Bombus lucorum, B. pratorum, B. agrorum and B. hortorum in a small area in west Scotland were assessed by counts of foraging bees made during three seasons and showed a partial division of the bee flora between the four species. 2. Seven of the factors which might lead to this division were investigated, either in the field or by experiments with artificial flowers visited by free-flying bees. 3. To three of these factors: colour, general shape and height of flower above the ground, the species reacted in the same way. To two other factors: presence or absence of nectar and degree of exposure of habitat, they responded differently, while competition between species also had a differential effect. All species are affected by the length relationship between tongue and corolla tube, but all pay most visits to flowers with a corolla tube considerably shorter than their tongue. 4. The differences between the species were as follows: lucorum visits open flowers, collects honeydew and `steals' nectar, forages in exposed habitats, collects pollen without nectar and is relatively uninfluenced by the presence of bees of other species. Hortorum is restricted to long-corolla-tubed flowers and unadapted psychologically for collecting pollen without nectar or for stealing. Pratorum visits mainly open flowers, forages in sheltered habitats, and is aggressive to other species. Agrorum visits flowers of intermediate corolla-tube length, forages in sheltered habitats later in the season than pratorum, and is retiring in its behaviour to other species.
Article
1. Lavender (Lavandula spp.) flowers attract more bumble bees (Bombus spp.) than honey bees (Apis mellifera). Counts of bees foraging on Lavandula × intermedia ‘Grosso’ at the University of Sussex campus, showed that bumble bees (92%) greatly outnumbered honey bees (8%). This was not due to a scarcity of honey bees, as the reverse ratio (94% honey bees vs. 6% bumble bees) occurred on borage (Borago officinalis) at the same location. 2. Video analysis of free-flying bees revealed that all bumble bee species present (Bombus terrestris/lucorum, Bombus pascuorum, and Bombus lapidarius) handled lavender flowers three times faster than honey bees (mean extraction times: 0.38, 0.37, 0.34 s respectively, vs. 1.30 s; all P <0.001). Honey bee tongue length (6.6 mm) was approximately 2mm shorter than those of bumble bees (7.8–8.9 mm) and 1mm shorter than the lavender corolla tube (c. 7 mm). In addition, bumble bees probed twice as many lavender flowers encountered than honey bees (86% vs. 46%). 3. Experimentally reducing effective corolla tube length with scalpel incisions significantly decreased extraction time for honey bees (from 1.11 to 0.76 s; P <0.001) but not for bumble bees (0.33 to 0.28 s; P =0.266). 4. Results suggest that honey bees are deterred from foraging on lavender because they are being outcompeted by bumble bees, which forage more efficiently.
Article
Spatiotemporal resource continuity promotes persistence of mobile animal populations. Current agricultural landscapes are poor in flowers resources for bumble bees. Available forage crops are predominantly early-season mass-flowering crops (MFC). It has been suggested, but not tested, that scarcity of late-season flower resources are limiting bumble bee populations. We examined whether addition of late-season flowering red clover affected worker, queen and male bumble bee densities. Bumble bees were surveyed in flower-rich uncultivated field borders across 24 landscapes (radius 2 km) with or without a clover field in the centre, varying in semi-natural grassland (SNG) and early MFC availability. Clover fields had over ten times higher worker densities compared to field borders, suggesting red clover as favoured forage. Five times more queens and 71% more males were found in landscapes with clover fields compared to control landscapes, despite these fields constituting less than 0.2% of the landscape area. Both MFC and SNG increased the density of males, but only in the presence of clover fields. Our results suggest that late-flowering red clover positively affects bumble bee reproduction, likely by increasing temporal resource continuity. Interventions such as flower strips can thus have mitigating effects if they release population regulation by late-season resource bottle-necks.
Article
Biological invasions represent both an increasingly important applied problem and a tool for gaining insight into the structure of ecological communities. Although competitive interactions between invasive and native species are considered among the most important mechanisms driving invasion dynamics, such interactions are in general poorly understood. The European honey bee (Apis mellifera) is a widespread and economically important invader long suspected to competitively suppress many native bee species. Yet the extent to which this introduced species alters native communities remains controversial, reflecting ongoing debate over the importance of resource competition in regulating pollinator populations. I experimentally tested the effects of competition with Apis on colony foraging behavior and reproductive success of a native eusocial bee, Bombus occidentalis Greene, in coastal California. B. occidentalis colonies located near experimentally introduced Apis hives had lower mean rates of forager return and a lower ratio of foraging trips for pollen relative to nectar. Both male and female reproductive success of B. occidentalis were also reduced with greater proximity to introduced Apis hives. Reproductive success correlated significantly with measures of colony foraging behavior, most strongly with the relative allocation of foraging effort to pollen collection. This pattern suggests that B. occidentalis colonies exposed to competition with Apis experienced increased nectar scarcity and responded by reallocating foragers from pollen to nectar collection, resulting in lowered rates of larval production. These results provide evidence that Apis competitively suppresses a native social bee known to be an important pollinator, with the potential for cascading effects on native plant communities. This work also contributes to a greater understanding of the role competitive interactions play in pollinator communities, particularly for social bees.
Article
If two species compete for two renewable resources, will they coevolve so as to make continued coexistence more likely? This question is analyzed using the equations of MacArthur (1972) but allowing the constants in those equations to undergo evolutionary change, subject to constraints. Individual selection will cause these variables to take values which are evolutionarily stable, in the sense that if all individuals in a population have those values no mutant can invade it. It is then possible to compare the evolutionarily stable values for each species on its own with the values when they coexist. Two cases are considered: a coarse-grained case in which at any instant a consumer can search for one resource or the other but not for both, and a fine-grained case in which both resources can be sought simultaneously. In both cases, each consumer in the absence of its competitor would evolve as a generalist. In competition, each consumer will coevolve as a specialist on a different resource patch type in the coarse-grained case, or, in the fine-grained environment, each consumer will become more specialized on one resource although not necessarily completely so. In the fine-grained case, it is possible for two generalists to coexist, but co-evolution will lead to character divergence. For the cases considered, the co-evolved divergence of the consumers leads to greater global stability of the consumer community even though it has negligible effect on the local Lyapunov stability. The increased community stability results from natural selection acting on individuals in the separate consumer populations. No group selection at either the population or community level is necessary.
Article
In selected foraging habitats of an agricultural landscape flower visits of bumblebees and community structure of foraging bumblebees were studied, with special regard to the role of crops as super-abundant resources. Most crops represent temporal foraging habitats with high abundance of bumblebees but mainly with low diversity in the bumblebee forage community, in contrast to permanent foraging habitats such as, for example, a hedgerow. The high numbers of bumblebees in the monoculture of crop plantations consisted mainly of short-tongued bumblebee species. The role of foraging distances for the visitation rate of foraging habitats was studied by performing capture–recapture experiments with natural nests of Bombus terrestris, Bombus lapidarius and Bombus muscorum. Differences were found on the species as well as the individual level. The foraging distances of B. muscorum were more restricted to the neighbourhood of the nesting habitat than the foraging activity of B. terrestris and B. lapidarius. High percentages of B. terrestris workers were recaptured while foraging on super-abundant resources in distances up to 1750 m from the nest. Isolated patches of highly rewarding forage crops, in agricultural landscapes, are probably only accessed by bumblebee species with large mean foraging distances, such as the short-tongued B. terrestris. Species like the rare, long-tongued B. muscorum depend on a close connection between nesting and foraging habitat. A restricted foraging radius might be one important factor of bumblebee species loss and potential pollinator limitation in modern agricultural landscapes. Furthermore, long-distance flights of bumblebee pollinators have to be considered in the present discussion on gene flow from transgenic plant species on a landscape scale.
Article
s Abstract Bees are generally regarded as beneficial insects for their role in pol-lination, and in the case of the honeybee Apis mellifera, for production of honey. As a result several bee species have been introduced to countries far beyond their home range, including A. mellifera, bumblebees (Bombus sp.), the alfalfa leafcutter bee Megachile rotundata, and various other solitary species. Possible negative conse-quences of these introductions include: competition with native pollinators for floral resources; competition for nest sites; co-introduction of natural enemies, particularly pathogens that may infect native organisms; pollination of exotic weeds; and disrup-tion of pollination of native plants. For most exotic bee species little or nothing is known of these possible effects. Research to date has focused mainly on A. mellifera, and has largely been concerned with detecting competition with native flower visitors. Considerable circumstantial evidence has accrued that competition does occur, but no experiment has clearly demonstrated long-term reductions in populations of native or-ganisms. Most researchers agree that this probably reflects the difficulty of carrying out convincing studies of competition between such mobile organisms, rather than a genuine absence of competitive effects. Effects on seed set of exotic weeds are easier to demonstrate. Exotic bees often exhibit marked preferences for visiting flowers of exotic plants. For example, in Australia and New Zealand many weeds from Europe are now visited by European honeybees and bumblebees. Introduced bees are primary pollinators of a number of serious weeds. Negative impacts of exotic bees need to be carefully assessed before further introductions are carried out.
Article
Summary • In intensively farmed agricultural landscapes, many species are confined to very small uncultivated areas such as field margins. However, it has been suggested that these small habitat elements cannot support viable populations of all the species observed there. Instead, species richness and abundance in these small habitat fragments may, at least partly, be dependent on dispersal from larger semi-natural grassland fragments. • We tested this hypothesis for butterflies and bumble bees in 12 independent landscapes in a region of intense agriculture in southern Sweden. In each landscape we surveyed abundance and species richness in one semi-natural grassland, one linear habitat (uncultivated field margin) adjacent to this (called proximate) and one similar linear habitat (called distant) situated at least 1000 m from the semi-natural grassland patch. • Both species richness and density (individuals per unit area) of butterflies and bumble bees were significantly higher in proximate linear habitats than in distant ones. Moreover, butterfly species richness was higher for a given area in grasslands than in any of the linear habitat types. Butterfly density in grasslands did not differ from that in proximate linear habitats but was lower in distant linear habitats. The effect of isolation on density was stronger for less mobile butterfly species. For bumble bees there was no difference in species richness between grasslands and proximate linear habitats. • For at least some of the butterfly species even these relatively small fragments of semi-natural grasslands act as population sources from which individuals disperse to the surrounding habitats and thereby contribute to higher densities and species richness in adjacent areas. For bumble bees, it is more likely that the grasslands contain a higher density of nests than the surrounding intensively cultivated landscape, and that the density of foraging bumble bees decreases with increasing distance from the nest. • Synthesis and application. Habitat fragmentation and intensified agricultural practices are considered to be a threat against services provided by pollinators. In order to sustain the abundance and diversity of insect pollinators in intensively farmed agricultural landscapes, we suggest that preservation of the remaining semi-natural grasslands or re-creation of flower-rich grasslands is essential. Journal of Applied Ecology (2007) 44, 50–59 doi: 10.1111/j.1365-2664.2006.01250.x
Article
Summary1. Linear regression models are an important statistical tool in evolutionary and ecological studies. Unfortunately, these models often yield some uninterpretable estimates and hypothesis tests, especially when models contain interactions or polynomial terms. Furthermore, the standard errors for treatment groups, although often of interest for including in a publication, are not directly available in a standard linear model.2. Centring and standardization of input variables are simple means to improve the interpretability of regression coefficients. Further, refitting the model with a slightly modified model structure allows extracting the appropriate standard errors for treatment groups directly from the model.3. Centring will make main effects biologically interpretable even when involved in interactions and thus avoids the potential misinterpretation of main effects. This also applies to the estimation of linear effects in the presence of polynomials. Categorical input variables can also be centred and this sometimes assists interpretation.4. Standardization (z-transformation) of input variables results in the estimation of standardized slopes or standardized partial regression coefficients. Standardized slopes are comparable in magnitude within models as well as between studies. They have some advantages over partial correlation coefficients and are often the more interesting standardized effect size.5. The thoughtful removal of intercepts or main effects allows extracting treatment means or treatment slopes and their appropriate standard errors directly from a linear model. This provides a simple alternative to the more complicated calculation of standard errors from contrasts and main effects.6. The simple methods presented here put the focus on parameter estimation (point estimates as well as confidence intervals) rather than on significance thresholds. They allow fitting complex, but meaningful models that can be concisely presented and interpreted. The presented methods can also be applied to generalised linear models (GLM) and linear mixed models.