Search

Future agriculture faces a twofold challenge: increasing yields to safeguard food security while simultaneously reducing its environmental impact. Ecological intensification has been proposed as a solution to this challenge. It entails the integration of ecosystem service management into farming practices to enhance or maintain yields while minimizing artificial inputs and environmental externalities. An increasing number of empirical studies have shown beneficial effects of ecosystem services on crop production, but the majority of these studies have focused on the effects of only a single ecosystem service in isolation. In contrast, in real-world agricultural systems, crop yield is shaped by several ecosystem services simultaneously. These different ecosystem services may interact (positively or negatively) and their interactions may furthermore depend on agricultural management practices. To assess the potential of ecological intensification in promoting yields and reducing external inputs, it is essential to understand the combined effects of different ecosystem services on agricultural production. The aim of this thesis was to examine whether and to what extent different ecosystem services interactively shape crop yield, and whether and how this is affected by agricultural management. Focusing on raspberry (Rubus idaeus L.), a globally important perennial fruit crop, I examined the potential interactive effects of the ecosystem services provided by insect pollinators, arbuscular mycorrhizal fungi (AMF) and soil organic matter (SOM) on the quantity and quality of raspberry production, and whether these effects were influenced by artificial fertilizer inputs.Natural relatives of commercial raspberry are widespread in temperate forests. These natural relatives depend entirely on several ecosystem services for survival and reproduction. Therefore, investigating the effects of ecosystem services on natural raspberry production would be informative to fully understan

The importance of wild pollinators compared to conventional agricultural management is undervalued, suggests the PhD thesis of Thijs Fijen of Wageningen University. A study in commercial leek seed production fields shows that wild pollinators contribute as much to crop yield as plant quality. Honeybees, placed next to flowering leek fields specifically for pollination, do not contribute much to crop yield. Experimental work confirmed these findings: a 50% reduction in pollination leads to much larger reductions in seed yield than similar reductions in fertilizer applications or irrigation. Surprisingly, a 50% reduction in fertilisation resulted in equally high, or higher crop yields. These results may explain the international trend that crop yields of insect-pollinated crops increase less fast as those of wind-pollinated crops. The research of Fijen furthermore shows that both crop pollination and pollinator biodiversity in agricultural landscapes can be promoted by better protection of semi-natural habitats such as flower-rich road sides and nature areas.

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 non‐crop habitats, and species’ 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 1.7‐ and 1.4‐fold respectively. Arable‐dominated landscapes with high edge densities achieved high yields. This suggests that enhancing edge density in European agroecosystems can promote functional biodiversity and yield‐enhancing ecosystem services.

Conserving and restoring semi-natural habitat, i.e. enhancing landscape complexity, is one of the main strategies to mitigate pollinator decline in agricultural landscapes. However, we still have limited understanding of how landscape complexity shapes pollinator communities in both crop and non-crop habitat, and whether pollinator responses to landscape complexity vary with their association with mass-flowering crops. Here, we surveyed pollinator communities on mass-flowering leek crops and in nearby semi-natural habitat in landscapes of varying complexity. Surveys were done before and during crop bloom and distinguished between pollinators that visit the crop frequently (dominant), occasionally (opportunistic), or not at all (non-crop). Forty-seven per cent of the species in the wider landscape were also observed on leek flowers. Crop pollinator richness increased with local pollinator community size and increasing landscape complexity, but relationships were stronger for opportunistic than for dominant crop pollinators. Relationships between pollinator richness in semi-natural habitats and landscape complexity differed between groups with the most pronounced positive effects on non-crop pollinators. Our results indicate that while dominant crop pollinators are core components of crop pollinator communities in all agricultural landscapes, opportunistic crop pollinators largely determine species-richness responses and complex landscapes are local hotspots for both biodiversity conservation and potential ecosystem service provision.

The current worldwide pollinator decline is caused by the interplay of different drivers. Several strategies have been undertaken to counteract or halt this decline, one of which is the implementation of wildflower fields. These supplementary flowers provide extra food resources and have proven their success in increasing pollinator biodiversity and abundance. Yet such landscape alterations could also alter the host–pathogen dynamics of pollinators, which could affect the populations. In this study, we investigated the influence of sown wildflower fields on the prevalence of micro-parasites and viruses in the wild bumble bee Bombus pascuorum, one of the most abundant bumble bee species in Europe and the Netherlands. We found that the effect of sown wildflower fields on micro-parasite prevalence is affected by the composition of the surrounding landscape and the size of the flower field. The prevalence of micro-parasites increases with increasing size of sown wildflower fields in landscapes with few semi-natural landscape elements. This effect was not observed in landscapes with a high amount of semi-natural landscape elements. We elaborate on two mechanisms which can support these findings: (1) “transmission hot spots” within the altered flower-networks, which could negatively impact hosts experiencing an increased exposure; (2) improved tolerance of the hosts, withstanding higher parasite populations.

Pollination by insects is a key input into many crops, with managed honeybees often being hired to support pollination services. Despite substantial research into pollination management, no European studies have yet explored how and why farmers managed pollination services and few have explored why beekeepers use certain crops. Using paired surveys of beekeepers and farmers in 10 European countries, this study examines beekeeper and farmer perceptions and motivations surrounding crop pollination. Almost half of the farmers surveyed believed they had pollination service deficits in one or more of their crops. Less than a third of farmers hired managed pollinators; however, most undertook at least one form of agri‐environment management known to benefit pollinators, although few did so to promote pollinators. Beekeepers were ambivalent towards many mass‐flowering crops, with some beekeepers using crops for their honey that other beekeepers avoid because of perceived pesticide risks. The findings highlight a number of largely overlooked knowledge gaps that will affect knowledge exchange and co‐operation between the two groups.

The sustainability of agriculture can be improved by integrating management of ecosystem services, such as insect pollination, into farming practices. However, large‐scale adoption of ecosystem services‐based practices in agriculture is lacking, possibly because growers undervalue the benefits of ecosystem services compared to those of conventional management practices. Here we show that, under representative real‐world conditions, pollination and plant quality made similar contributions to marketable seed yield of hybrid leek (Allium porrum). Relative to the median, a 25% improvement of plant quality and pollination increased crop value by an estimated $18 007 and $17 174 ha−1 respectively. Across five crop lines, bumblebees delivered most pollination services, while other wild pollinator groups made less frequent but nevertheless substantial contributions. Honeybees actively managed for pollination services did not make significant contributions. Our results show that wild pollinators are an undervalued agricultural input and managing for enhancing pollinators makes sense economically in high‐revenue insect‐pollinated cropping systems.

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

De laatste tijd is er veel aandacht voor de achteruitgang van bijen. Er zijn inmiddels veel initiatieven om wilde bijen een handje te helpen, meestal door het inzaaien van bloemenmengsels. Maar profiteren wilde bijen hier wel van? Welke soorten hebben daar het meest baat bij? Bevordert dit ook de bestuiving van naastgelegen gewassen? En waar moet rekening mee gehouden worden bij het aanleggen en beheren van een goede bloemenstrook? Aan de hand van literatuuronderzoek is naar antwoorden gezocht.

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.

Radboud Universiteit Nijmegen, 18 september 2015, Promotores : Siepel, H., Schaminee, J.H.J. Co-promotor : Kleijn, D., Contains fulltext : 143958.pdf (publisher's version ) (Open Access)

Species distribution models (SDM) are increasingly used to understand the factors that regulate variation in biodiversity patterns and to help plan conservation strategies. However, these models are rarely validated with independently collected data and it is unclear whether SDM performance is maintained across distinct habitats and for species with different functional traits. Highly mobile species, such as bees, can be particularly challenging to model. Here, we use independent sets of occurrence data collected systematically in several agricultural habitats to test how the predictive performance of SDMs for wild bee species depends on species traits, habitat type, and sampling technique. We used a species distribution modeling approach parametrized for the Netherlands, with presence records from 1990 to 2010 for 193 Dutch wild bees. For each species, we built a Maxent model based on 13 climate and landscape variables. We tested the predictive performance of the SDMs with independent datasets collected from orchards and arable fields across the Netherlands from 2010 to 2013, using transect surveys or pan traps. Model predictive performance depended on species traits and habitat type. Occurrence of bee species specialized in habitat and diet was better predicted than generalist bees. Predictions of habitat suitability were also more precise for habitats that are temporally more stable (orchards) than for habitats that suffer regular alterations (arable), particularly for small, solitary bees. As a conservation tool, SDMs are best suited to modeling rarer, specialist species than more generalist and will work best in long-term stable habitats. The variability of complex, short-term habitats is difficult to capture in such models and historical land use generally has low thematic resolution. To improve SDMs’ usefulness, models require explanatory variables and collection data that include detailed landscape characteristics, for example, variability of crops and flowe

1. Growing evidence for declines in wild bees calls for the development and implementation of effective mitigation measures. Enhancing floral resources is a widely accepted measure for promoting bees in agricultural landscapes, but effectiveness varies considerably between landscapes and regions. We hypothesize that this variation is mainly driven by a combination of the direct effects of measures on local floral resources and the availability of floral resources in the surrounding landscape. 2. To test this, we established wildflower strips in four European countries, using the same seed mixture of forage plants specifically targeted at bees. We used a before–after control–impact approach to analyse the impacts of wildflower strips on bumblebees, solitary bees and Red List species and examined to what extent effects were affected by local and landscape-wide floral resource availability, land-use intensity and landscape complexity. 3. Wildflower strips generally enhanced local bee abundance and richness, including Red-listed species. Effectiveness of the wildflower strips increased with the local contrast in flower richness created by the strips and furthermore depended on the availability of floral resources in the surrounding landscape, with different patterns for solitary bees and bumblebees. Effects on solitary bees appeared to decrease with increasing amount of late-season alternative floral resources in the landscape, whereas effects on bumblebees increased with increasing early-season landscape-wide floral resource availability. 4. Synthesis and applications. Our study shows that the effects of wildflower strips on bees are largely driven by the extent to which local flower richness is increased. The effectiveness of this measure could therefore be enhanced by maximizing the number of bee forage species in seed mixtures, and by management regimes that effectively maintain flower richness in the strips through the years. In addition, for bumblebees specificall

The following information was missing from the funding section: BBSRC, DEFRA, NERC, the Scottish Government and the Wellcome Trust, under the Insect Pollinators Initiative crops project. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Evidence for declining populations of both wild and managed bees has raised concern about a potential global pollination crisis. Strategies to mitigate bee loss generally aim to enhance floral resources. However, we do not really know whether loss of preferred floral resources is the key driver of bee decline because accurate assessment of host plant preferences is difficult, particularly for species that have become rare. Here we examine whether population trends of wild bees in The Netherlands can be explained by trends in host plants, and how this relates to other factors such as climate change. We determined host plant preference of bee species using pollen loads on specimens in entomological collections that were collected before the onset of their decline, and used atlas data to quantify population trends of bee species and their host plants. We show that decline of preferred host plant species was one of two main factors associated with bee decline. Bee body size, the other main factor, was negatively related to population trend, which, because larger bee species have larger pollen requirements than smaller species, may also point toward food limitation as a key factor driving wild bee loss. Diet breadth and other potential factors such as length of flight period or climate change sensitivity were not important in explaining twentieth century bee population trends. These results highlight the species-specific nature of wild bee decline and indicate that mitigation strategies will only be effective if they target the specific host plants of declining species.

Ongeveer de helft van de Nederlandse bijensoorten staat op de Rode Lijst. Tegelijkertijd gaan de honingbijen die traditioneel landbouwgewassen bestuiven sterk achteruit. In hoeverre kunnen de wilde bijensoorten deze leemte voor de landbouw invullen? Dit artikel geeft een overzicht van de kennis hierover tot nu toe. De economische waarde van bestuiving van voedselgewassen door insecten wordt in Europa op € 22 miljard geschat (Gallai et al., 2009), in Nederland op circa €1,1miljard (Blacquière, 2010). Van de bloembezoekende insecten dragen bijen veruit het meest bij aan de bestuiving van landbouwgewassen.