POLLINATORS POLLINATION AND FOOD PRODUCTION

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THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION Accuracy of FAO data most likely differs among countries and crops. However, under-reporting or over-reporting of agricultural data among countries and crops should be considered as a random error source and should not modify interpretation of temporal and spatial trends to the extent that these biases are not consistent among countries, crops, or years. Even consistent biases would affect neither the shape of the temporal trends nor estimates of pollinator dependency at the country level to the extent that biases do not differ between pollinator-dependent and nondependent crops. The other component of the estimation of agriculture pollinator dependency, i.e., the extent to which crop yield depends on pollinators, is also subjected to great uncertainty. Crops can be solely classified in broadly-defined categories of pollinator dependency because information is highly fragmentary, anecdotal or scarce for many crops, for many present and past varieties within crops, because the degree of pollinator dependence can be highly variable among and within varieties of a single crop (McGregor, 1976; Klein et al., 2007). Therefore, for some major crops, such as soybean and sunflower, their pollinator dependence status should be viewed as a consensus status for the whole crop based on existing published information. In any case, this component of uncertainty should have a minor role in global or country-level estimations of pollinator dependency because of the weighted average of many individual observations (i.e., crops). TABLE 3.2 Pollinator dependency, and world production and global cultivated area (2012) of 16 major crops based on FAO dataset (FAOSTAT 2013). We also provide estimates of annual growth rates in production and cultivated area (1961-2012). Pollinator dependency categories followed Klein et al. (2007). 184 3. THE STATUS AND TRENDS IN POLLINATORS AND POLLINATION Category/Crop Vegetables and tubers Potatoes Scientific name Solanum tuberosum Pollinator dependency Production (millions of tonnes) Annual growth in production (%/year) Cultivated area (millions of hectares) None 365.37 0.59 19.28 -0.27 Sugar beet Beta vulgaris None 269.83 1.02 4.91 -0.67 Cassava Tomatoes Cucumbers and gherkins Cereals Manihot esculenta Lycopersicon esculentum None 269.13 2.64 2.08 1.52 Little 161.79 3.53 4.80 2.08 Cucumis sativus Great 65.13 3.84 2.11 1.45 Maize Zea mais None 872.79 2.88 178.55 1.04 Rice Wheat Barley Biofuels and oilseeds Sugar cane Oryza ssp. (mainly O. sativa) Triticum spp. (mainly T. aestivum, T. durum, T. spelta) Hordeum disticum Saccharum officinarum None 738.19 2.44 162.32 0.67 None 671.50 2.19 217.32 0.12 None 133.51 1.21 49.57 -0.19 None 1842.26 2.81 26.09 2.13 Oilpalm (fruit) Elaeis guineensis Little 259.42 5.95 17.57 3.15 Soybeans Glycine max, G. soja Rapeseed Brassica rapa, B. napus oleifera Fresh fruit Modest 241.14 4.40 104.92 2.95 Modest 64.56 5.83 34.10 3.37 Watermelon Citrullus lanatus Essential 105.37 3.54 3.47 1.13 Apples Malus domestica Great 76.38 2.98 4.84 2.05 Oranges Citrus sinensis Little 68.22 2.89 3.82 2.19 Mangoes, mangosteens, guavas Mangifera indica, Garcinia mangostana, Psidium guajava Great 42.14 2.69 5.17 2.77 Annual growth in area (%/year)
THE ASSESSMENT REPORT ON POLLINATORS, POLLINATION AND FOOD PRODUCTION 3.8 TRENDS IN CROP POLLINATION AND YIELD 3.8.1 Outline of section probably the largest pollination industry. In this nation, more than two million honey-bee colonies are rented and even moved across the country to pollinate crops (Morse and Calderone, 2000). In fact, approximately 1.7 million hives are transported to California for almond pollination during a six-week period (Sumner and Boriss, 2006). Deficits in pollination quantity and/or quality often limit crop yield. This section reviews and discusses the relevance of pollinator diversity to narrow pollination deficits, and whether crop pollination deficits have increased along spatial disturbance gradients and over time. It also briefly discusses the impact on agriculture of bees that were introduced outside their native range and have become invasive. 3.8.2 Crop pollination deficits In pollination, pollen can be insufficient in quantity, e.g. stigmas receive too few pollen grains, or quality, e.g. stigmas receive pollen with low vigour due to genetic (i.e., self or selfincompatible pollen) or environmental factors (e.g., pollen produced by water-stressed or defoliated plants). Both may restrict wild plant reproduction and crop yield (Knight et al., 2005; Chapter 1). Technically, a crop pollination deficit refers to quantitative or qualitative inadequate pollen receipt that limits agricultural output (Vaissière et al., 2011). Even though pollination commonly limits seed production, decreases in pollinator diversity and visitation by effective pollinators may exacerbate chronic pollination deficits experienced by many crops. A recent worldwide meta-analysis including data for 41 crops grown in 600 cultivated fields distributed across all continents, except Antarctica, reveals that diverse assemblages of wild bees seem to be important to reduce pollination deficits and sustain high yields of many pollinatordependent crops (Garibaldi et al., 2013). Specifically, this study found that flower visitation by wild bees increases crop fruit and seed set, on average, twice as much as visitation by the domesticated honey bee, Apis mellifera, on a per-visit basis. Furthermore, declining pollination provided by wild bees might not be substituted by stocking fields with more honey bee hives, although honey bees can add to the pollination provided by wild bees (Garibaldi et al., 2013). Whereas complementary pollinating activity between wild bees and honey bees can explain this overall additive effect, diverse pollinator assemblages ensure the inclusion of one or more species of efficient pollinators (see also Chapter 1). For instance, yield of marketable French bean production in the Mt Kenya region was found to be positively correlated with the abundance of carpenter bees (Xylocopa spp.), despite high abundance of honey bees (Masiga et al., 2014). On the other hand, the risks of relying on a single pollinator species for large-scale crop pollination are exemplified by almond (Prunus dulcis) in the US, the country with Besides questioning the efficiency of honey bees in pollinating almond flowers compared to wild pollinators (Klein et al., 2012), the continuous drop of the stock of honey-bee hives in the US during the last decades (National Research Council, 2007) questions the rationality and sustainability of such a practice. Furthermore, at a global scale the growth of the stock of domesticated honey-bees hives have proceeded at a much lower rate than demands for pollination (Aizen and Harder, 2009a), stressing the importance of wild pollinators for the productivity of many pollinator-dependent crops (Breeze et al., 2011). Similarly, in some regions of several Asian countries people have resorted to hand pollination of apple following declines in native apple pollinators and unavailability of managed honey bees to perform this function (Partap and Partap, 2007). A recent global analysis (Kleijn et al., 2015), which includes data from 20 pollinator-dependent crops in about 1400 crop fields, proposes that the contribution of wild bees to crop production is limited to a subset of bee species that are common in agroecosystems. It seems likely that (i) crop pollination deficits are common and (ii) enhanced and sustained yields of many crops can be better ensured by both promoting specific pollinator species and the maintenance and restoration of diverse pollinator communities. 3.8.3 Spatial and temporal trends in pollination deficits Remnants of natural and semi-natural habitats, hedgerows, and field margins, which supply essential flowering and nesting resources, can become important pollinator sources in different agro-ecosystems (Winfree et al., 2009; Morandin and Kremen, 2013; see Chapter 2). Therefore, increasing distance from field edges into crop fields greatly reduces flower visitation and the number of visiting species (Ricketts et al., 2008; Garibaldi et al., 2011a). On average, bee visitation rates and richness are reduced by half at distances about 670 and 1500m, respectively, from natural vegetation (Ricketts et al., 2008). As a consequence, not only does average crop yield often decrease with distance to field margins or natural vegetation (albeit at lower rates than pollinator abundance and richness), but it also becomes less predictable (Garibaldi et al., 2011a). A long-term survey conducted in Scandinavia also revealed trends in the composition and diversity of bumble bee communities and crop yield. Bumble bees are important pollinators in 185 3. THE STATUS AND TRENDS IN POLLINATORS AND POLLINATION
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POLLINATORS POLLINATION AND FOOD PRODUCTION

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