Providing key resources to animals may enhance both their biodiversity and the ecosystem services they provide. We examined the performance of annual flower strips targeted at the promotion of ...natural pest control in winter wheat. Flower strips were experimentally sown along 10 winter wheat fields across a gradient of landscape complexity (i.e. proportion non-crop area within 750 m around focal fields) and compared with 15 fields with wheat control strips. We found strong reductions in cereal leaf beetle (CLB) density (larvae: 40%; adults of the second generation: 53%) and plant damage caused by CLB (61%) in fields with flower strips compared with control fields. Natural enemies of CLB were strongly increased in flower strips and in part also in adjacent wheat fields. Flower strip effects on natural enemies, pests and crop damage were largely independent of landscape complexity (8–75% non-crop area). Our study demonstrates a high effectiveness of annual flower strips in promoting pest control, reducing CLB pest levels below the economic threshold. Hence, the studied flower strip offers a viable alternative to insecticides. This highlights the high potential of tailored agri-environment schemes to contribute to ecological intensification and may encourage more farmers to adopt such schemes.
Impacts of climate change on individual species are increasingly well documented, but we lack understanding of how these effects propagate through ecological communities. Here we combine species ...distribution models with ecological network analyses to test potential impacts of climate change on >700 plant and animal species in pollination and seed-dispersal networks from central Europe. We discover that animal species that interact with a low diversity of plant species have narrow climatic niches and are most vulnerable to climate change. In contrast, biotic specialization of plants is not related to climatic niche breadth and vulnerability. A simulation model incorporating different scenarios of species coextinction and capacities for partner switches shows that projected plant extinctions under climate change are more likely to trigger animal coextinctions than vice versa. This result demonstrates that impacts of climate change on biodiversity can be amplified via extinction cascades from plants to animals in ecological networks.
The western honey bee (Apis mellifera) is the most frequent floral visitor of crops worldwide, but quantitative knowledge of its role as a pollinator outside of managed habitats is largely lacking. ...Here we use a global dataset of 80 published plant–pollinator interaction networks as well as pollinator effectiveness measures from 34 plant species to assess the importance of A. mellifera in natural habitats. Apis mellifera is the most frequent floral visitor in natural habitats worldwide, averaging 13% of floral visits across all networks (range 0–85%), with 5% of plant species recorded as being exclusively visited by A. mellifera. For 33% of the networks and 49% of plant species, however, A. mellifera visitation was never observed, illustrating that many flowering plant taxa and assemblages remain dependent on non-A. mellifera visitors for pollination. Apis mellifera visitation was higher in warmer, less variable climates and on mainland rather than island sites, but did not differ between its native and introduced ranges. With respect to single-visit pollination effectiveness, A. mellifera did not differ from the average non-A. mellifera floral visitor, though it was generally less effective than the most effective non-A. mellifera visitor. Our results argue for a deeper understanding of how A. mellifera, and potential future changes in its range and abundance, shape the ecology, evolution, and conservation of plants, pollinators, and their interactions in natural habitats.
1. Sown flower strips are increasingly implemented within agri-environment schemes (AES) to increase functional biodiversity and ecosystem services such as pollination or natural pest control, but ...their effectiveness in achieving these goals remains poorly studied. 2. We tested the performance of experimentally sown annual flower strips specifically designed to promote natural enemies of aphids and their pest control services (tailored flower strips) in adjacent potato crops (n = 8) compared with control fields (n = 10). Flower strips consisted of 11 plant species providing abundant floral and extra-floral resources. 3. The abundance of key natural enemies of aphids (hoverflies, lacewings and ladybirds) and hoverfly species richness was greatly enhanced in tailored flower strips compared with potato control strips. This resulted in an average increase in the number of eggs deposited by hoverflies and lacewings by 127% and 48%, respectively, and a reduction in the number of aphids by 75% in adjacent potato crops. 4. Synthesis and applications. We conclude that tailored flower strips can be an effective agrienvironmental measure to enhance natural enemies and aphid control in nearby crops. Indeed, tailored flower strips may help to reduce insecticide input in potato production as they significantly decrease the probability that action thresholds are reached. Promoting natural enemy abundance and diversity, as observed for hoverflies, may increase the stability of pest control and provide additional benefits to agro-ecosystems in terms of natural enemy conservation. We thus recommend establishing tailored flower strips as a promising management option to reconcile the objectives of ecological intensification and biodiversity conservation.
Understanding the functional consequences of biodiversity loss is a major goal of ecology. Animal-mediated pollination is an essential ecosystem function and service provided to mankind. However, ...little is known how pollinator diversity could affect pollination services. Using a substitutive design, we experimentally manipulated functional group (FG) and species richness of pollinator communities to investigate their consequences on the reproductive success of an obligate out-crossing model plant species, Raphanus sativus. Both fruit and seed set increased with pollinator FG richness. Furthermore, seed set increased with species richness in pollinator communities composed of a single FG. However, in multiple-FG communities, highest species richness resulted in slightly reduced pollination services compared with intermediate species richness. Our analysis indicates that the presence of social bees, which showed roughly four times higher visitation rates than solitary bees or hoverflies, was an important factor contributing to the positive pollinator diversity–pollination service relationship, in particular, for fruit set. Visitation rate at different daytimes, and less so among flower heights, varied among social bees, solitary bees and hoverflies, indicating a niche complementarity among these pollinator groups. Our study demonstrates enhanced pollination services of diverse pollinator communities at the plant population level and suggests that both the niche complementarity and the presence of specific taxa in a pollinator community drive this positive relationship.
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•Repeated X-ray imaging of wild ground-nesting bee nests in their natural habitat.•Quantification of temporal evolution of solitary and social bee nest architecture.•Burrowing by bees ...significantly alters soil structure.•Solitary species built simple burrows, social species built complex burrow networks.•Bee burrows in the soil can persist for at least 16 months.
Most research on wild bees has focused on their role as pollinators, while their importance as soil ecosystem engineers has been largely overlooked, despite the fact that most species nest in the soil. There is limited quantitative knowledge regarding the architecture of nests created by wild bees and the temporal evolution of bee burrows. The aim of this study was to evaluate the feasibility of repeatedly scanning ground-nesting bee nests using X-ray computed tomography to quantify the morphology and temporal evolution of burrow systems created by both solitary and social species. We installed eleven large cylinders at locations with ongoing nesting activity of ground-nesting bees, and repeatedly scanned these soil columns with a medical X-ray scanner over a period of 16 months. From the X-ray images, we extracted bee burrows to visualize and quantitatively characterize their morphology and temporal evolution. The architecture and temporal evolution of burrows strongly differed between the studied social and solitary ground-nesting bee species. Burrows created by the solitary species were simple, linear and unbranched burrows, which were not reused and decayed with time. The burrow systems created by the social species were more complex, with highly branched networks of horizontal and vertical burrows, which increased in complexity and size over time during the bee activity period. The persistence of burrows created by ground-nesting bees varied greatly, with some decaying within a few weeks and others remaining mostly intact for the entire 16-month study period. This study demonstrates the potential of X-ray imaging to provide new insights into the underground life of ground-nesting bees, and highlights the locally important role of ground-nesting bees as soil ecosystem engineers.
Forelands of retreating glaciers offer an ideal model system to study community assembly processes during primary succession. As plants colonize the area that is freed from ice they should be ...accompanied by their pollinators to successfully reproduce and spread. However, little is known about the assembly of plant-pollinator networks. We therefore used quantitative network analysis to study the structure of plant-pollinator interactions at seven sites representing a chronosequence from 8 to 130 years since deglaciation on the foreland of the Morteratsch glacier (southeastern Switzerland). At these sites, individual visits of plant flowers by insects were recorded throughout the flowering season. Species richness of insect-pollinated plants and plant-pollinating insects, together with measures of interaction diversity and evenness, increased along the chronosequence at least for the first 80 years after deglaciation. Bees were the most frequent flower visitors at the two youngest sites, whereas flies dominated in mature communities. Pollinator generalization (the number of visited plant species weighted by interaction strength), but not plant generalization, strongly increased during the primary succession. This was reflected in a pronounced decline in network level specialization (measured as Blüthgen's H₂') and interaction strength asymmetry during the first 60 years along the chronosequence, while nestedness increased along the chronosequence. Thus, our findings contradict niche-theoretical predictions of increasing specialization of pollination systems during succession, but are in agreement with expectations from optimal foraging theory, predicting an increase in pollinator generalization with higher plant diversity but similar flower abundance, and an increase in diet breadth at higher pollinator densities during primary succession.
Continuous availability of food resources, such as pollen, is vital for many insects that provide pollination and pest control services to agriculture. However, there is a lack of knowledge about the ...shared or complementary use of floral resources by such species, which hampers more effective landscape management to simultaneously promote them in agroecosystems.
Here, we simultaneously quantified pollen use by a bumblebee (Bombus terrestris) and a mason bee (Osmia bicornis), two bee species recognized as important crop pollinators, as well as a lacewing (Chrysoperla carnea) and a ladybeetle species (Harmonia axyridis), both common predators of crop aphids, throughout the season in 23 agricultural landscapes in Germany and Switzerland.
Pollen diets were more diverse and similar among C. carnea and H. axyridis compared to the two bee species, but all four species shared key pollen types early in the season such as Acer, Quercus, Salix and Prunus. All species exhibited a pronounced shift in pollen sources from primarily woody plants (mainly trees) in spring to primarily herbaceous plants in summer. The majority of pollen (overall ≥64%) came from non‐agricultural plants even in crop‐dominated landscapes.
Synthesis and applications. Our results highlight the importance of trees as pollen sources for many insect species, particularly early in the season. Our findings support incentives that promote heterogeneous agricultural landscapes including both woody and herbaceous semi‐natural habitats, ensuring phenological complementarity of floral resources for insect species that can provide pollination and pest control services to agriculture. The identified key plant species can help to design and optimize agri‐environment schemes to promote these functionally important insects.
•Reproduction of two Osmia species increased with landscape-wide pollen availability.•Woody semi-natural habitats contributed disproportionately to the Osmia diet.•Benefits of forest proximity to ...Osmia indicated functions beyond pollen supply.•Resource and land cover maps help to understand the spatial ecology of wild bees.
Floral resources are crucial for wild pollinators. Identifying the spatio-temporal floral resource use of wild pollinators and effects of resource distribution on their development might help to promote them and their pollination services to crops in agricultural landscapes.
We established populations of Osmia cornuta and Osmia bicornis, two solitary wild bees, in 24 agricultural landscapes with varying floral resource availability. Based on their pollen use, we mapped the landscape-scale distribution of the visited plants, estimated pooled specific floral resource availabilities and measured its effects on reproductive output.
Woody semi-natural habitats such as hedgerows provided the majority of pollen sources for both Osmia species. Pollen use differed strongly between the two species. The offspring of both Osmia increased with availability of pooled specific pollen resources. In accordance with their preferred pollen types, offspring of O. cornuta increased with increasing cover of trees and shrubs of the Rosaceae family, and that of O. bicornis with increasing cover of Papaver rhoeas, Ranunculus acris and Quercus spp. as well as with the proximity to oilseed rape. In spite of their specific responses to pollen resources, the offspring of both species decreased with the distance to forest. The floral resource availability did not significantly affect the proportion of adult females and the weight of the offspring. As forest does not appear to be a main foraging habitat for both species, the benefit of forest proximity indicates an additional role of forest in addition to food availability.
Specific flowering plants and forests should thus be conserved and enhanced to maintain and support O. cornuta, O. bicornis and likely other wild bee populations in agricultural landscapes. The combined information of land cover and detailed floral resource availability gives a deeper understanding into population processes in agricultural landscapes.
Climate and land-use changes are main drivers of insect declines, but their combined effects have not yet been quantified over large spatiotemporal scales. We analysed changes in the distribution ...(mean occupancy of squares) of 390 insect species (butterflies, grasshoppers, dragonflies), using 1.45 million records from across bioclimatic gradients of Switzerland between 1980 and 2020. We found no overall decline, but strong increases and decreases in the distributions of different species. For species that showed strongest increases (25% quantile), the average proportion of occupied squares increased in 40 years by 0.128 (95% credible interval: 0.123-0.132), which equals an average increase in mean occupancy of 71.3% (95% CI: 67.4-75.1%) relative to their 40-year mean occupancy. For species that showed strongest declines (25% quantile), the average proportion decreased by 0.0660 (95% CI: 0.0613-0.0709), equalling an average decrease in mean occupancy of 58.3% (95% CI: 52.2-64.4%). Decreases were strongest for narrow-ranged, specialised, and cold-adapted species. Short-term distribution changes were associated to both climate changes and regional land-use changes. Moreover, interactive effects between climate and regional land-use changes confirm that the various drivers of global change can have even greater impacts on biodiversity in combination than alone. In contrast, 40-year distribution changes were not clearly related to regional land-use changes, potentially reflecting mixed changes in local land use after 1980. Climate warming however was strongly linked to 40-year changes, indicating its key role in driving insect trends of temperate regions in recent decades.
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