27 research outputs found
Managing trap-nesting bees as crop pollinators : Spatiotemporal effects of floral resources and antagonists
The decline of managed honeybees and the rapid expansion of mass-flowering crops increase the risk of pollination limitation in crops and raise questions about novel management approaches for wild pollinators in agroecosystems. Adding artificial nesting sites, such as trap nests, can promote cavity-nesting bees in agroecosystems, but effectiveness could be limited by the availability of floral resources in the surrounding landscape and by natural antagonists. In two European regions, we exposed artificial trap nests in paired field boundaries adjacent to oilseed rape (OSR) fields or non-flowering crops for 2 years within 32 landscapes covering two independent gradients of OSR cover and semi-natural habitat (SNH) cover in the landscape. We analysed the effects of local and landscape-wide floral resource availability, land-use intensity, landscape complexity and natural antagonists on community composition and population dynamics of trap-nesting bees. Numbers of brood cells showed a strong, three-fold increase in response to the additional nesting sites. Species richness and abundance of cavity-nesting bees that were active during OSR flowering increased significantly with increasing amounts of early season landscape-wide floral resource availability, such as the cultivation of OSR. Later foraging species benefited instead from the availability of late-season alternative flower resources or SNH cover once the mass-flowering had ceased. Density-dependent parasitism increased following mass-flowering, while no density-dependent effect was found during mass-flowering. Structural equation modelling revealed that the influence of floral resource availability on community growth rate was mediated by community size. Community size showed a strong negative effect on community growth rate. Despite positive density-dependent parasitism, antagonists had only weak regulating effects on community growth rate. Synthesis and applications. Trap-nesting bee populations grow markedly with the increasing availability of food resources in the landscape and effectiveness of trap nests is only marginally limited by natural antagonists. Thus, trap nests could be a simple pollinator-supporting strategy to accompany the current expansion of mass-flowering crops and to ensure pollination services for insect-pollinated crops. Trap nests benefit, not only early season active generalist bees during oilseed rape flowering, but also species with later phenology if accompanied by other pollinator-supporting practices.</p
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Plant-pollinator networks in semi-natural grasslands are resistant to the loss of pollinators during blooming of mass-flowering crops
Mass-flowering crops lead to spatial redistributions of pollinators and to transient shortages within nearby semi-natural grasslands, but the impacts on plantâpollinator interactions remain largely unexplored. Here, we characterised which pollinator species are attracted by oilseed rape and how this affected the structure of plantâpollinator networks in nearby grasslands. We surveyed 177 networks from three countries (Germany, Sweden and United Kingdom) in 24 landscapes with high crop cover, and compared them to 24 landscapes with low or no oilseed rape during and after crop blooming. On average 55% of grassland pollinator species were found on the crop, which attracted 8â35% of individuals away from grasslands. However, networks in the grasslands were resistant to these reductions, since mainly abundant and highly mobile species were attracted. Nonetheless, simulations indicated that network structural changes could be triggered if > 50% of individuals were attracted to the crop (a value well-above that found in our study system), which could affect community stability and resilience to further disturbance
Mass-flowering crops dilute pollinator abundance in agricultural landscapes across Europe
Mass-flowering crops (MFCs) are increasingly cultivated and might influence pollinator communities in MFC fields and nearby semi-natural habitats (SNHs). Across six European regions and 2 years, we assessed how landscape-scale cover of MFCs affected pollinator densities in 408 MFC fields and adjacent SNHs. In MFC fields, densities of bumblebees, solitary bees, managed honeybees and hoverflies were negatively related to the cover of MFCs in the landscape. In SNHs, densities of bumblebees declined with increasing cover of MFCs but densities of honeybees increased. The densities of all pollinators were generally unrelated to the cover of SNHs in the landscape. Although MFC fields apparently attracted pollinators from SNHs, in landscapes with large areas of MFCs they became diluted. The resulting lower densities might negatively affect yields of pollinator-dependent crops and the reproductive success of wild plants. An expansion of MFCs needs to be accompanied by pollinator-supporting practices in agricultural landscapes
Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor
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The interplay of landscape composition and configuration: new pathways to manage functional biodiversity and agroecosystem services across Europe
Managing agricultural landscapes to support biodiversity and ecosystem services is a key aim of a sustainable agriculture. However, how the spatial arrangement of crop fields and other habitats in landscapes impacts arthropods and their functions is poorly known. Synthesising data from 49 studies (1515 landscapes) across Europe, we examined effects of landscape composition (% habitats) and configuration (edge density) on arthropods in fields and their margins, pest control, pollination and yields. Configuration effects interacted with the proportions of crop and nonâcrop habitats, and speciesâ dietary, dispersal and overwintering traits led to contrasting responses to landscape variables. Overall, however, in landscapes with high edge density, 70% of pollinator and 44% of natural enemy species reached highest abundances and pollination and pest control improved 1.7â and 1.4âfold respectively. Arableâdominated landscapes with high edge densities achieved high yields. This suggests that enhancing edge density in European agroecosystems can promote functional biodiversity and yieldâenhancing ecosystem services
Delivery of crop pollination services is an insufficient argument for wild pollinator conservation
There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments
Landschafts-Spillover von BestÀubern aus Raps auf ackerbaulich genutzte und naturnahe Habitate auf verschiedenen zeitlichen Ebenen
Organisms use different resources in different habitat types during their life cycle. Thereby, they connect habitats and provide ecosystem services or disservices in several habitat types. In agricultural landscapes, the spillover of organisms, i.e. movement of an organism and its function from one habitat to another, especially from semi-natural to managed habitats, is one of the most important processes that influence population dynamics and community composition. Importantly, spillover connects habitats not only spatially, but also on different temporal scales, because availability of resources changes over time in agricultural landscapes, e.g. by mass-flowering events of crops, harvesting or crop rotation. Most often, semi-natural habitats are seen as beneficial source of organisms, but also managed habitats can provide valuable resources, and thereby initiate spillover to other habitats. Mass-flowering crops, like oil-seed rape, are such valuable feeding resources for pollinators, and pollinators might spillover from oil-seed rape to other habitats which provide alternative foraging resources. The focus of this dissertation was to evaluate the influence of oil-seed rape on pollinators in agricultural landscapes by studying effects (1) on different temporal scales (from effects during the flowering period of oil-seed rape, Chapter II & IV, to intermediate effects on a second mass-flowering crop, Chapter III, to spillover effects to the flowering period in the next year, Chapter IV), (2) semi-natural (Chapter II) and crop (Chapter III, IV) habitats, and (3) on various pollinator groups which differ in their life cycle (Chapter II, III, IV).
In this dissertation effects from oil-seed rape on all temporal scales â in the short term during mass-flowering and in the long term on a late-flowering crop and even in the next year on oil-seed rape fields â were found. These effects might be important for crop and wild plant pollination, and pollinator conservation. Importantly, the effects on different temporal scales depend on the considered habitat (managed or different semi-natural habitats) and on the investigated pollinator group. The more pollinators match the flowering period of oil-seed rape in their activity period and the more dependent they are on flowering resources in their life cycle, the more pronounced are their responses. Effects were found for wild bees, but not for hoverflies and honey bees. Moreover, the availability of semi-natural habitats in the landscape is important and may modulate effects from oil-seed rape. The longevity of effects of oil-seed rape shows the importance of including several temporal scales into ecosystem-service studies, not only for pollinators, but also for other ecosystem-service providing species groups.Organismen nutzen wĂ€hrend ihres Lebens verschiedene Ressourcen in unterschiedlichen Habitaten. Dabei verbinden sie Habitate miteinander und erbringen positive oder negative Ăkosystemdienstleistungen in verschiedenen Habitattypen. In Agrarlandschaften ist der âSpilloverâ von Organismen, d.h. die Bewegung von Organismen und die gleichzeitige Verschiebung ihrer Funktion von einem Habitat in ein anderes, insbesondere von naturnahen Habitaten hin zu landwirtschaftlich genutzten Habitaten, einer der wichtigsten Prozesse, die die Populationsdynamik und Zusammensetzung von Gemeinschaften beeinflussen. Zu betonen ist, dass Spillover Habitate nicht nur rĂ€umlich, sondern auch auf unterschiedlichen zeitlichen Skalen verbindet, da sich die VerfĂŒgbarkeit von Ressourcen in Agrarlandschaften ĂŒber die Zeit, z.B. durch die MassenblĂŒte von FeldfrĂŒchten, die Ernte oder die Fruchtfolge, verĂ€ndert. Meist werden naturnahe Habitate als wertvolle Quelle von Organismen betrachtet, aber auch landwirtschaftlich genutzte Habitate können wertvolle Ressourcen zur VerfĂŒgung stellen und damit den Spillover von Organismen in andere Habitate initiieren. Massentrachten, wie Raps, sind solche wertvollen Ressourcen fĂŒr BestĂ€uber. BestĂ€uber können von Rapsfeldern auf andere Habitate ĂŒberschwappen, die ihnen alternative Futterquellen bieten. Der Schwerpunkt dieser Dissertation liegt auf der Beurteilung des Einflusses von Raps auf BestĂ€uber in Agrarlandschaften anhand der Betrachtung von Effekten (1) auf unterschiedlichen zeitlichen Ebenen (von Effekten wĂ€hrend der BlĂŒhperiode des Rapses, Kapitel II & IV, ĂŒber mittelfristige Effekte auf eine zweite blĂŒhende Feldfrucht, Kapitel III, bis hin zu Spillover-Effekten in die BlĂŒhperiode des nĂ€chsten Jahres, Kapitel IV), (2) in naturnahen (Kapitel II) und landwirtschaftlich genutzten (Kapitel III, IV) Habitaten und (3) fĂŒr unterschiedliche BestĂ€ubergruppen, die sich in ihrem Lebenszyklus unterscheiden (Kapitel II, III, IV).
In dieser Dissertation wurden Effekte von Raps auf allen untersuchten zeitlichen Ebenen gefunden â sowohl kurzfristig wĂ€hrend der RapsblĂŒte als auch langfristig in einer spĂ€tblĂŒhenden Massentracht und sogar im nĂ€chsten Jahr wĂ€hrend der RapsblĂŒte. Diese Effekte können Folgen fĂŒr die BestĂ€ubung von Kultur- und Wildpflanzen und auch fĂŒr den Schutz von BestĂ€ubern haben. Es ist wichtig, darauf hinzuweisen, dass die Effekte auf unterschiedlichen zeitlichen Ebenen abhĂ€ngig von dem untersuchten Habitat (landwirtschaftlich genutzte, verschiedene naturnahe Habitate), sowie der untersuchten BestĂ€ubergruppe sind. Je mehr die BestĂ€uber in ihrer AktivitĂ€tsperiode mit der BlĂŒtezeit von Raps ĂŒbereinstimmen und je mehr sie auf BlĂŒtenressourcen in ihrem Lebenszyklus angewiesen sind, umso gröĂer scheint ihre Reaktion. Effekte wurden fĂŒr Wildbienen, nicht aber fĂŒr Schwebfliegen und Honigbienen gefunden. DarĂŒber hinaus ist auch die VerfĂŒgbarkeit von naturnahen Habitaten in der Landschaft wichtig und kann die Effekte des Rapses beeinflussen. Die Langlebigkeit der Effekte von Raps zeigt die Bedeutung der Integration von unterschiedlichen zeitlichen Ebenen in die Untersuchung von Ăkosystem-Dienstleistungen, nicht nur fĂŒr BestĂ€uber, sondern auch fĂŒr andere Artengruppen, die Ăkosystem-Dienstleistungen erbringen
Early mass-flowering crops mitigate pollinator dilution in late-flowering crops
Previous studies focused mainly on the provision of ecosystem services by species movements between semi-natural and managed habitats, whereas data on spillover effects between two managed habitats or between habitats that provide target resources in non-overlapping time periods are lacking. We studied densities of three pollinator groups on sunflower fields as a late mass-flowering crop in 16 landscapes that differed in the relative cover of oil-seed rape as an early mass-flowering crop, in the relative cover of sunflowers and in the relative cover of semi-natural habitats. Our aim was to evaluate dynamics between two crops with non-overlapping flowering periods. Densities of bumble bees in late-flowering sunflower fields were enhanced by early-flowering oil-seed rape. Highest bumble bee densities in the late-flowering crop were reached in landscapes that combined high relative covers of oil-seed rape and semi-natural habitats. Further, low relative covers of oil-seed rape in spring led to decreased bumble bee densities in late-flowering sunflower fields in landscapes with high relative covers of sunflower fields (dilution effect), whereas in landscapes with high relative covers of oil-seed rape, no dilution of bumble bees was found. Thus, our results indicate that early mass-flowering crops can mitigate pollinator dilution in crops flowering later in the season. We conclude that the management of landscape-scale patterns of early and late mass-flowering crops together with semi-natural habitats could be used to ensure crop pollination services. Similar processes could also apply for other species groups and may be an important, but so far disregarded, determinant of population densities in agroecosystems
Data from: Biological pest control and yields depend on spatial and temporal crop cover dynamics
1. Modern agricultural landscapes are dynamic systems with interannually changing proportions of different crop types. However, the effects of spatiotemporal changes in crop area on crop yields and cropâherbivoreâantagonist interactions have been rarely considered, in contrast to documented beneficial effects of semi-natural habitats on biological pest control at local and landscape scales. In this study, we examined how the proportion of oilseed rape (OSR) fields in a landscape and the annual increase or decrease in OSR cover due to crop rotation affect OSR herbivores, their natural enemies and crop yield. 2. During two study years, we examined the abundance of adult and larval pollen beetles, parasitism of pollen beetle larvae by a parasitic ichneumonid and crop yields (seed weight per plant) in the edge and centre of 36 OSR fields. The fields differed in the proportion of OSR in the surrounding landscape at 1-km radius and in the interannual change in the proportion of OSR from the previous year to the respective study year. 3. Adult pollen beetle abundance decreased in one study year and larval pollen beetle abundance and parasitism rates decreased in both study years with spatially increasing OSR proportion in the landscape, indicating dilution effects on both trophic levels. Crop yield was positively affected by spatially increasing proportions of OSR. An interannual increase in the proportion of OSR led to the dilution of pest species, but had no significant effect on yield or parasitism rate. 4. Synthesis and applications. The negative effects of pollen beetles on yields despite regular insecticide applications underpin the need for improved techniques for controlling this pest. Our results emphasize the potential to enhance crop yields by the management of spatiotemporal crop cover dynamics within landscapes. We recommend that future management schemes should coordinate the spatial aggregation and annual dynamics of oilseed rape (OSR) cover in a landscape as a potential way to reduce pest impacts in intensively managed OSR fields
Data from: Managing trap-nesting bees as crop pollinators: spatiotemporal effects of floral resources and antagonists
1. The decline of managed honeybees and the rapid expansion of mass-flowering crops increase the risk of pollination limitation in crops and raise questions about novel management approaches for wild pollinators in agroecosystems. Adding artificial nesting sites, such as trap nests, can promote cavity-nesting bees in agroecosystems, but effectiveness could be limited by the availability of floral resources in the surrounding landscape and by natural antagonists.
2. In two European regions, we exposed artificial trap nests in paired field boundaries adjacent to oilseed rape (OSR) fields or non-flowering crops for two years within 32 landscapes covering two independent gradients of OSR cover and semi-natural habitat (SNH) cover in the landscape. We analysed the effects of local and landscape-wide floral resource availability, land-use intensity, landscape complexity and natural antagonists on community composition and population dynamics of trap-nesting bees.
3. Number of brood cells showed a strong, three-fold increase in response to the additional nesting sites. Species richness and abundance of cavity-nesting bees that were active during OSR flowering increased significantly with increasing amount of early-season landscape-wide floral resource availability, such as the cultivation of OSR. Later foraging species benefited instead from the availability of late-season alternative flower resources or SNH cover once the mass-flowering had ceased. Density-dependent parasitism increased following mass-flowering, while no density-dependent effect was found during mass-flowering.
4. Structural equation modelling revealed that the influence of floral resource availability on community growth rate was mediated by community size. Community size showed a strong negative effect on community growth rate. Despite positive density-dependent parasitism, antagonists had only weak regulating effects on community growth rate.
5. Synthesis and applications. Trap-nesting bee populations grow markedly with the increasing availability of food resources in the landscape and effectiveness of trap nests is only marginally limited by natural antagonists. Thus, trap nests could be a simple pollinator-supporting strategy to accompany the current expansion of mass-flowering crops, and to ensure pollination services for insect-pollinated crops. Trap nests benefit not only early season active generalist bees during oilseed rape flowering but also species with later phenology if accompanied by other pollinator-supporting practices