The loss of floral resources is a leading cause of wild bee decline in agricultural landscapes, but little is known about the temporal aspects of floral resource limitation for both social and ...solitary bees. Understanding when floral resources are most needed is crucial for the optimal design of pollinator conservation measures.
We surveyed bees and flowers in 160 semi‐natural habitat patches multiple times per year (May–July) for 5 years. We identified the seasonality of floral resources and wild bees and examined inter‐ and intra‐annual patterns of floral resource limitation at both local and landscape scales.
Floral resource availability varied across years but generally peaked in late May, after which it declined and remained low through July.
Bumblebee and solitary bee abundances increased across the season, leading to stronger floral resource limitation for both groups later in the season. Bumblebee abundance was marginally positively associated with the cumulative amount of landscape‐scale floral resources as well as the floral resources of the previous year. Solitary bee abundance was only predicted by local‐scale floral resources.
Synthesis and applications: Our results indicate that agri‐environmental management should target the provision of summer floral resources for both social and solitary bees. Local‐scale enhancement of floral resources can likely benefit solitary bees, but bumblebees probably require the management of floral resources at the landscape scale. Increasing the floral resources and the flowering period of herbaceous habitats that cover large proportions of the landscape, such as pastures, has the greatest potential to improve summer floral resources for bees.
Our results indicate that agri‐environmental management should target the provision of summer floral resources for both social and solitary bees. Local‐scale enhancement of floral resources can likely benefit solitary bees, but bumblebees probably require the management of floral resources at the landscape scale. Increasing the floral resources and the flowering period of herbaceous habitats that cover large proportions of the landscape, such as pastures, has the greatest potential to improve summer floral resources for bees.
Agricultural intensification is one of the main drivers of farmland bird declines, but effects on birds may be confounded with those of climate change. Here we examine the effects of intensification ...and climate change on a grassland breeding wader, the Black-tailed Godwit Limosa l. limosa, in the Netherlands. Population decline has been linked to poor chick survival which, in turn, has been linked to available foraging habitat. Foraging habitat of the nidifugous chicks consists of uncut grasslands that provide cover and arthropod prey. Conservation measures such as agri-environment schemes aim to increase the availability of chick foraging habitat but have not yet been successful in halting the decline. Field observations show that since the early 1980s, farmers advanced their first seasonal mowing or grazing date by 15 days, whereas Godwits did not advance their hatching date. Ringing data indicate that between 1945 and 1975 hatching dates advanced by about 2 weeks in parallel with the advancement of median mowing dates. Surprisingly, temperature sums at median mowing and hatching dates suggest that while the agricultural advancement before 1980 was largely due to agricultural intensification, after 1980 it was largely due to climate change. Examining arthropod abundance in a range of differently managed grasslands revealed that chick food abundance was little affected but that food accessibility in intensively used tall swards may be problematic for chicks. Our results suggest that, compared with 25 years ago, nowadays (1) a much higher proportion of clutches and chicks are exposed to agricultural activities, (2) there is little foraging habitat left when chicks hatch and (3) because of climate change, the vegetation in the remaining foraging habitat is taller and denser and therefore of lower quality. This indicates that for agri-environment schemes to make a difference, they should not only be implemented in a larger percentage of the breeding area than the current maxima of 20-30% but they should also include measures that create more open, accessible swards.
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.
Significance Growing concern about bee declines and associated loss of pollination services has increased the urgency to identify the underlying causes. So far, the identification of the key drivers of decline of bee populations has largely been based on speculation. We assessed the relative importance of a range of proposed factors responsible for wild bee decline and show that loss of preferred host plant species is one of the main factors associated with the decline of bee populations in The Netherlands. Interestingly, species foraging on crop plant families have stable or increasing populations. These results indicate that mitigation strategies for loss of wild bees will only be effective if they target the specific host plants of declining bee species.
In the past decades, large-scale conservation programs have been implemented to halt the decline of farmland species. The mechanisms explaining the eff ectiveness of these programs remain poorly ...understood. Here we test the recent hypothesis that the eff ects of conservation management are determined by the ecological contrasts in limiting resources they create relative to the baseline situation. We examine responses of wintering seed-eating farmland birds to the experimental establishment of winter food plots in areas with contrasting food availability. We found that farmland bird abundance and species richness were strongly positively related to seed availability, regardless of compositional diff erences between agricultural landscapes. In line with the ecological contrast hypothesis, the responses of wintering farmland birds increased with increasing conservation induced contrast in a key limiting resource. Both contrasts and relative responses were negatively related to baseline food availability, but the absolute bird density in food plots was unrelated to baseline food availability. Th is indicates that both relative and absolute eff ects of conservation management need to be considered to properly evaluate the eff ectiveness of conservation management.
•Wild bird seed mixtures support a wide range of over-wintering farmland birds.•Farmland specialists benefit most from concentrated conservation measures.•Common and widespread species benefit most ...from scattered conservation actions.•Effective conservation may require a combination of concentrated and scattered management.
A key issue in conservation is where and how much management should be implemented to obtain optimal biodiversity benefits. Cost-effective conservation requires knowledge on whether biodiversity benefits are higher when management is concentrated in a few core areas or scattered across the landscape, and how these effects vary between species. To address these questions, we examined species-specific behavioural responses of over-wintering farmland birds to enhanced seed availability. In a two-year experiment we first examined the relationship between landscape-scale seed availability and farmland bird density. Then we investigated the relative resource delivery (difference in bird densities between landscapes with and without additional management) and the efficiency (number of individuals supported per unit management) of conservation actions, both at the landscape-scale (ca 100ha) and at the scale of the conservation measures (3.6ha). The conservation actions were targeted towards ten seed-eating farmland bird species, but we also considered the responses of seven non-targeted and more generalist seed-eating species, seven species that are less dependent on seeds and three species of birds of prey. We found a positive relationship between bird density and landscape-scale seed availability for eleven species and, for four of these species, the slope of this relationship changed before and after a threshold seed density. For two seed-eating specialists, the number of individuals using conservation patches declined with landscape-scale seed availability. In addition, we found that the relative resource delivery declined with landscape scale seed availability for three seed-eating specialists and was independent of landscape-scale seed availability in four other species. Our results suggest that farmland specialists may benefit most from winter food additions if conservation actions result in high landscape-scale seed availability. This may be achieved by concentrating conservation measures or by establishing measures in areas with high baseline seed availability. By contrast, species that can utilize a wider range of habitats and resources may benefit more from scattering measures across larger areas. Therefore, optimal management for the full range of farmland birds in wintertime may require a combination of core areas with concentrated management and more widely distributed smaller patches of conservation measures.
•Drosophila suzukii and parasitoid wasp abundance increase with landscape complexity.•Pesticide effectiveness might be reduced in highly complex agroecosystems.•High mobility of D. suzukii across ...agricultural landscapes.•Low impact of conservation biological control (CBC) on D. suzukii management.•Long-term effects of CBC practices on invasive pest species remain unexplored.
Agricultural landscapes rich in natural and semi-natural habitats promote biodiversity and important ecosystem services for crops such as pest control. However, semi-natural habitats may fail to deliver these services if agricultural pests are disconnected from the available pool of natural enemies, as may be the case with invasive species. This study aimed to provide insights into the relationship between landscape complexity and the abundance of the recently established invasive pest species Drosophila suzukii and a group of natural enemies (parasitoid wasps), which contain species that parasitize D. suzukii in native and invaded ecosystems. The importance of landscape complexity was examined at two spatial scales. At the field scale, the response to introduction of wildflower strips was analysed, while the relationship with forest cover was assessed at the landscape scale. Half of the surveys were done next to blueberry crops (Vaccinium corymbosum), the other half was done in landscapes without fruit crops to examine effects of D. suzukii host presence. As expected, the number of observed parasitoid wasps increased with amount of forest surrounding the blueberry fields, but the number of D. suzukii individuals likewise increased with forest cover. Establishment of wildflower strips did not significantly affect the abundance of D. suzukii or parasitoid wasps and insect phenology was similar in landscapes with and without blueberry crops. This suggests that D. suzukii is enhanced by landscape complexity and is largely unlinked from the species group that, in its native range, hosts key natural enemies. Although management practices that rely on enhancing natural enemies through habitat manipulations can contribute to the long-term stability of agroecosystems and to control agricultural pests, other control measures may still be necessary in the short term to counteract the benefits obtained by D. suzukii from natural habitats.
European populations of Common hamster (
Cricetus cricetus
) have dramatically declined in the last decades, and in many EU countries, the species is on the brink of extinction. In the Netherlands, a ...research and reintroduction program was started in three areas with hamster-friendly management to reverse the decline of the species. Since 2002, more than 800 captive-bred and wild-born hamsters were monitored using implant radiotransmitters to quantify survival rates and discover the main causes of death after release compared to those of wild individuals. Individuals with a transmitter were regularly checked at their burrow. Predation by foxes, birds of prey, and small mustelids was the most important cause of mortality of this medium-sized rodent, while crop type and harvest regime were also likely to be important drivers as they influenced survival rates through the presence or absence of protective cover. The fitted weekly survival model showed that male hamsters had much lower survival rates during the active season than females, which corresponds with the ‘risky male hypothesis’. Survival rates of females appeared too low to keep populations at a stable level. To establish a viable population, more optimal environmental conditions for both survival and reproduction of the hamsters are necessary. Using electric fences around fields with hamsters significantly increased the survival of females. However, hamster conservationists need to consider not just subadult and adult survival rates, but also habitat connectivity, weather effects on reproduction, and alternative agricultural practices on a landscape scale.
Wildflower strips have been heralded as a promising way to enhance ecosystem services by providing organisms which may help make farming less dependent on external inputs. However, recent studies ...show inconsistent effects on delivery of ecosystem services and crop yield, warranting a more detailed analysis of the factors determining the effects of wildflower strips. We examined how the natural enemy groups of spider, carabid beetle and staphylinid beetle, as well as aphid pest and crop yield respond to wildflower strips. We furthermore determined whether the response of natural enemies, aphids and crop yield depends on flower cover and species richness, and how this is influenced by fertilizer and insecticide applications to the crop in 16 winter wheat fields in the Netherlands. We used an experimental approach with a nested design that included all combinations of wildflower strips (present/absent), fertilizer application (yes/no) and insecticide application (yes/no). Presence of wildflower strips did not affect ground-dwelling natural enemies, aphids or crop yield. However, flower availability across wildflower strips and control margins was positively related to the abundance of the pooled number of examined natural enemies, spiders and carabid beetles. Positive effects in the crop were observed over limited distances; up to 5 m from the edge for spiders and wheat yield. The effects of flower availability and on-field management practices on natural enemies, aphids and wheat yield did not interact suggesting that, in our study, effects of flowers were not influenced by insecticide or fertilizer applications but were mainly additive. Our study indicates that cover and richness of wildflowers in field margin habitat, rather than establishment of wildflower strips per se, drove increases in natural enemies and crop yield. This suggests that more attention should be given to the optimization of establishment success of seed mixtures and management practices enhancing wildflower cover and diversity. Furthermore, biodiversity enhancing management of the herbaceous vegetation in linear landscape elements may represent a cost-effective alternative to boost ecosystem services regulating crop production in agricultural landscapes.
•The abundance of natural enemies is positively related with flower cover and species richness in field boundaries.•Crop yield next to flower-rich field boundaries is 15% higher than next to flower-poor ones, but only in the crop edge.•Effects of wildflowers in field boundaries on crop yield are additive to those of fertilizer application.
Farmland is a major land cover type in Europe and Africa and provides habitat for numerous species. The severe decline in farmland biodiversity of the last decades has been attributed to changes in ...farming practices, and organic and low‐input farming are assumed to mitigate detrimental effects of agricultural intensification on biodiversity. Since the farm enterprise is the primary unit of agricultural decision making, management‐related effects at the field scale need to be assessed at the farm level. Therefore, in this study, data were collected on habitat characteristics, vascular plant, earthworm, spider, and bee communities and on the corresponding agricultural management in 237 farms in 13 European and two African regions. In 15 environmental and agricultural homogeneous regions, 6–20 farms with the same farm type (e.g., arable crops, grassland, or specific permanent crops) were selected. If available, an equal number of organic and non‐organic farms were randomly selected. Alternatively, farms were sampled along a gradient of management intensity. For all selected farms, the entire farmed area was mapped, which resulted in total in the mapping of 11 338 units attributed to 194 standardized habitat types, provided together with additional descriptors. On each farm, one site per available habitat type was randomly selected for species diversity investigations. Species were sampled on 2115 sites and identified to the species level by expert taxonomists. Species lists and abundance estimates are provided for each site and sampling date (one date for plants and earthworms, three dates for spiders and bees). In addition, farmers provided information about their management practices in face‐to‐face interviews following a standardized questionnaire. Farm management indicators for each farm are available (e.g., nitrogen input, pesticide applications, or energy input). Analyses revealed a positive effect of unproductive areas and a negative effect of intensive management on biodiversity. Communities of the four taxonomic groups strongly differed in their response to habitat characteristics, agricultural management, and regional circumstances. The data has potential for further insights into interactions of farmland biodiversity and agricultural management at site, farm, and regional scale.
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