Bees provide essential pollination services that are potentially affected both by local farm management and the surrounding landscape. To better understand these different factors, we modelled the relative effects of landscape composition (nesting and floral resources within foraging distances), landscape configuration (patch shape, interpatch connectivity and habitat aggregation) and farm management (organic vs. conventional and local‐scale field diversity), and their interactions, on wild bee abundance and richness for 39 crop systems globally. Bee abundance and richness were higher in diversified and organic fields and in landscapes comprising more high‐quality habitats; bee richness on conventional fields with low diversity benefited most from high‐quality surrounding land cover. Landscape configuration effects were weak. Bee responses varied slightly by biome. Our synthesis reveals that pollinator persistence will depend on both the maintenance of high‐quality habitats around farms and on local management practices that may offset impacts of intensive monoculture agriculture.

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.

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Hermaphroditic individuals can produce both selfed and outcrossed progeny, termed mixed mating. General theory predicts that mixed-mating populations should evolve quickly toward high rates of selfing, driven by rapid purging of genetic load and loss of inbreeding depression (ID), but the substantial number of mixed-mating species observed in nature calls this prediction into question. Lower average ID reported for selfing than for outcrossing populations is consistent with purging and suggests that mixed-mating taxa in evolutionary transition will have intermediate ID. We compared the magnitude of ID from published estimates for highly selfing (r > 0.8), mixed-mating (0.2 ≤ r ≥ 0.8), and highly outcrossing (r < 0.2) plant populations across 58 species. We found that mixed-mating and outcrossing taxa have equally high average lifetime ID (δ = 0.58 and 0.54, respectively) and similar ID at each of four life-cycle stages. These results are not consistent with evolution toward selfing in most mixed-mating taxa. We suggest that prevention of purging by selective interference could explain stable mixed mating in many natural populations. We identify critical gaps in the empirical data on ID and outline key approaches to filling them.

Summary• Reduced allocation to structures for pollinator attraction is predicted in selfing species. We explored the association between outcrossing and floral display in a broad sample of angiosperms. We used the demonstrated relationship to test for bias against selfing species in the outcrossing rate distribution, the shape of which has relevance for the stability of mixed mating.• Relationships between outcrossing rate, flower size, flower number and floral display, measured as the product of flower size and number, were examined using phylogenetically independent contrasts. The distribution of floral displays among species in the outcrossing rate database was compared with that of a random sample of the same flora.• The outcrossing rate was positively associated with the product of flower size and number; individually, components of display were less strongly related to outcrossing. Compared with a random sample, species in the outcrossing rate database showed a deficit of small floral display sizes.• We found broad support for reduced allocation to attraction in selfing species. We suggest that covariation between mating systems and total allocation to attraction can explain the deviation from expected trade-offs between flower size and number. Our results suggest a bias against estimating outcrossing rates in the lower half of the distribution, but not specifically against highly selfing species.

Original Citation:A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes Published version:DOI:10.1111/gcb.13714 Terms of use:Open Access (Article begins on next page) Anyone can freely access the full text of works made available as "Open Access". Works made available under a Creative Commons license can be used according to the terms and conditions of said license. Use of all other works requires consent of the right holder (author or publisher) if not exempted from copyright protection by the applicable law. Agricultural intensification is a leading cause of global biodiversity loss, which can reduce the provisioning of ecosystem services in managed ecosystems. Organic farming and plant diversification are farm management schemes that may mitigate potential ecological harm by increasing species richness and boosting related ecosystem services to agroecosystems. What remains unclear is the extent to which farm management schemes affect biodiversity components other than species richness, and whether impacts differ across spatial scales and landscape contexts. Using a global meta-dataset, we quantified the effects of organic farming and plant diversification on abundance, local diversity (communities within fields), and regional diversity (communities across fields) of arthropod pollinators, predators, herbivores, and detritivores. Both organic farming and higher in-field plant diversity enhanced arthropod abundance, particularly for rare taxa. This resulted in increased richness but decreased evenness. While these responses were stronger at local relative to regional scales, richness and abundance increased at both scales, and richness on farms embedded in complex relative to simple landscapes. Overall, both organic farming and in-field plant diversification exerted the strongest effects on pollinators and predators, suggesting these management schemes can facilitate ecosystem service providers without augmenting herbivore (pest) populations. Our results suggest that organic farming and plant diversification promote diverse arthropod metacommunities that may provide temporal and spatial stability of ecosystem service provisioning. Conserving diverse plant and arthropod communities in farming systems therefore requires sustainable practices that operate both within fields and across landscapes. Availability: This is the author's manuscript

Summary1 Plant species may become invasive due to a lack of natural enemies (e.g. herbivores) in their introduced range. Absence of herbivores may result in selection for the loss of costly herbivore-resistance traits, which are expected to show a trade-off with vigour or competitive ability (the evolution of increased competitive ability, or EICA, hypothesis). 2 We conducted a common garden experiment in Switzerland, in which we compared herbivore resistance and vigour of Senecio jacobaea plants exposed to the specialist flea beetle Longitarsus jacobaeae , for four populations originating within the native range (Europe), and four from regions where it had been introduced (New Zealand, USA) and was unaffected by L. jacobaeae . Our predictions were that, compared with plants from the native populations, plants from introduced populations would experience greater herbivory (due to loss of resistance traits), and exhibit more vigorous growth. 3 As expected, we found that introduced S. jacobaea grew larger, and had greater reproductive output, than plants from the native range. Larger plants experienced more feeding damage, and introduced plants were consumed more even when size differences were controlled. Introduced plants also exhibited a greater relative ability to reproduce after damage was sustained, i.e. higher tolerance to herbivory. 4 Contrary to predictions, however, plants from introduced populations had higher total pyrrolizidine alkaloid production (chemical defence against herbivores). 5 Although plants from introduced ranges exhibited life-history traits consistent with EICA predictions, similar phenotypes were common in one of the populations from the native range, suggesting that EICA may not fully explain the invasion success of S. jacobaea . 6 Our results imply that increased competitive ability (vigour) of invasive plants may be associated with changes in resistance as well as tolerance to herbivory, and both types of anti-herbivore defence may need to be examined simultaneously to advance our understanding of invasiveness.

Most of the world's crops depend on pollinators, so declines in both managed and wild bees raise concerns about food security. However, the degree to which insect pollination is actually limiting current crop production is poorly understood, as is the role of wild species (as opposed to managed honeybees) in pollinating crops, particularly in intensive production areas. We established a nationwide study to assess the extent of pollinator limitation in seven crops at 131 locations situated across major crop-producing areas of the USA. We found that five out of seven crops showed evidence of pollinator limitation. Wild bees and honeybees provided comparable amounts of pollination for most crops, even in agriculturally intensive regions. We estimated the nationwide annual production value of wild pollinators to the seven crops we studied at over $1.5 billion; the value of wild bee pollination of all pollinator-dependent crops would be much greater. Our findings show that pollinator declines could translate directly into decreased yields or production for most of the crops studied, and that wild species contribute substantially to pollination of most study crops in major crop-producing regions.