The diversity and abundance of wild insect pollinators have declined in many agricultural landscapes. Whether such declines reduce crop yields, or are mitigated by managed pollinators such as honey bees, is unclear. We found universally positive associations of fruit set with flower visitation by wild insects in 41 crop systems worldwide. In contrast, fruit set increased significantly with flower visitation by honey bees in only 14% of the systems surveyed. Overall, wild insects pollinated crops more effectively; an increase in wild insect visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation. Visitation by wild insects and honey bees promoted fruit set independently, so pollination by managed honey bees supplemented, rather than substituted for, pollination by wild insects. Our results suggest that new practices for integrated management of both honey bees and diverse wild insect assemblages will enhance global crop yields.

/pdf/wild-pollinators-enhance-fruit-set-of-crops-regardless-of-3jinwkjshm.pdf

Wild Pollinators Enhance Fruit Set of Crops Regardless of Honey Bee Abundance

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.

/pdf/a-global-quantitative-synthesis-of-local-and-landscape-50t2426u54.pdf

A global quantitative synthesis of local and landscape effects on wild bee pollinators in agroecosystems

The 2011 Human Development Report argues that the urgent global challenges of sustainability and equity must be addressed together – and identifies policies on the national and global level that could spur mutually reinforcing progress towards these interlinked goals. Bold action is needed on both fronts, the Report contends, if the recent human development progress for most of the world’s poor majority is to be sustained, for the benefit of future generations as well as for those living today. Past Reports have shown that living standards in most countries have been rising – and converging – for several decades now. Yet the 2011 Report projects a disturbing reversal of those trends if environmental deterioration and social inequalities continue to intensify, with the least developed countries diverging downwards from global patterns of progress by 2050.The Report shows further how the world’s most disadvantaged people suffer the most from environmental degradation, including in their immediate personal environment, and disproportionately lack political power, making it all the harder for the world community to reach agreement on needed global policy changes. The Report also outlines great potential for positive synergies in the quest for greater equality and sustainability, especially at the national level. The Report further emphasizes the human right to a healthy environment, the importance of integrating social equity into environmental policies, and the critical importance of public participation and official accountability. The 2011 Report concludes with a call for bold new approaches to global development financing and environmental controls, arguing that these measures are both essential and feasible.

Human Development Report 2011. Sustainability and Equity: A Better Future for All

Biodiversity-ecosystem functioning experiments have established that species richness and composition are both important determinants of ecosystem function in an experimental context. Determining whether this result holds for real-world ecosystem services has remained elusive, however, largely due to the lack of analytical methods appropriate for large-scale, associational data. Here, we use a novel analytical approach, the Price equation, to partition the contribution to ecosystem services made by species richness, composition and abundance in four large-scale data sets on crop pollination by native bees. We found that abundance fluctuations of dominant species drove ecosystem service delivery, whereas richness changes were relatively unimportant because they primarily involved rare species that contributed little to function. Thus, the mechanism behind our results was the skewed species-abundance distribution. Our finding that a few common species, not species richness, drive ecosystem service delivery could have broad generality given the ubiquity of skewed species-abundance distributions in nature.

/pdf/abundance-of-common-species-not-species-richness-drives-27ncr2169e.pdf

Abundance of common species, not species richness, drives delivery of a real‐world ecosystem service

Functional complementarity and specialisation: The role of biodiversity in plant–pollinator interactions

Flower visitation and pollination by animals are the first steps and therefore critical to the sexual reproduction of many plant species (Kearns et al. 1998), including up to 90 per cent of Angiosperms in tropical rainforests (Bawa 1990). Flower visitors are insects or vertebrates like hummingbirds or bats visiting flowers for receiving nectar and/or pollen, and the visitation can, but does not necessarily, result in pollination, the successful fertilization of the flower. Recent estimates showed that 35 per cent of global food production directly consumed by humans comes from crops that benefit from flower visitation, primarily by bees and other insects (Klein et al. 2007). Many of these crop plants increase fruit or seed quantity from 5–50 per cent when flower visitors are present under experimental conditions, and a small number of crops (n 1⁄4 13) do not set fruit at all if pollinators are absent. Flower visitors can be also important for our dairy and meat industries, since many forage crops, like alfalfa, clover (Delaplane and Mayer 2000), and soybeans produced for cattle forage (Chiari et al. 2005) benefit from insect pollination for seed production. Flower visitors are also often important in modern agriculture to mediate gene flow between varieties in hybrid seed production (Greenleaf and Kremen 2006a, Van Deynze et al. 2005). Many wild plant populations have been shown to be limited by access to flower visitors (Ashman et al. 2004). Intensification of land use by tilling, irrigation, and fertilizer and biocide use, along with declining habitat heterogeneity from increased field sizes, monoculture plantings, and the modification of natural habitats by humans, significantly impacts pollinator communities across a variety of scales (Klein et al. 2007, Kremen et al. 2007, Ricketts et al. 2008). Local (field-level) alterations that impact pollinators and pollination include changes in: (1) the abundance and distribution of flower resources (Holzschuh et al. 2007, Klein et al. 2002, Williams and Kremen 2007, Tylianakis et al. 2008), (2) species richness of flowering plants (Ebeling et al. 2008, Ghazoul 2006, Potts et al. 2006), (3) availability of nesting sites and materials (Shuler et al. 2005, Kim et al. 2006), (4) light levels (Klein et al. 2003a, b), and (5) temporal continuity of floral resources (Greenleaf and Kremen 2006b). Examples of landscape-level factors affecting bee communities are the proportion and quality of natural or seminatural habitats in the landscape (Greenleaf and Kremen 2006b, Kim et al. 2006, Kremen et al. 2002, 2004), the distance of natural or semi-natural habitats from crop systems (Klein et al. 2003a, b, Ricketts et al. 2004, Ricketts et al. 2008), and the presence of mass-flowering resources (Herrman et al. 2007, Westphal et al. 2003). Therefore, resource availability and the area and isolation of natural habitats are all important for the conservation of pollinator species richness, which provides a key service to crop production. In this chapter, we discuss what is known about the relationship between flower-visiting species richness and pollination services. Following the introduction (Section 14.1), the relative importance of species richness, individual numbers, and combined effects in providing services to their mutualistic

Understanding the role of species richness for crop pollination services

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Understanding the role of species richness for crop pollination services