Importance of pollinators in changing landscapes for world crops

Abstract

The extent of our reliance on animal pollination for world crop production for human food has not previously been evaluated and the previous estimates for countries or continents have seldom used primary data. In this review, we expand the previous estimates using novel primary data from 200 countries and found that fruit, vegetable or seed production from 87 of the leading global food crops is dependent upon animal pollination, while 28 crops do not rely upon animal pollination. However, global production volumes give a contrasting perspective, since 60% of global production comes from crops that do not depend on animal pollination, 35% from crops that depend on pollinators, and 5% are unevaluated. Using all crops traded on the world market and setting aside crops that are solely passively self-pollinated, wind-pollinated or parthenocarpic, we then evaluated the level of dependence on animal-mediated pollination for crops that are directly consumed by humans. We found that pollinators are essential for 13 crops, production is highly pollinator dependent for 30, moderately for 27, slightly for 21, unimportant for 7, and is of unknown significance for the remaining 9. We further evaluated whether local and landscape-wide management for natural pollination services could help to sustain crop diversity and production. Case studies for nine crops on four continents revealed that agricultural intensification jeopardizes wild bee communities and their stabilizing effect on pollination services at the landscape scale.

Figure 1

Crop selection pathway to estimate the annual world production that is influenced by animal pollination (electronic supplementary material 1; lower left side) and to evaluate the levels of dependence on animal pollination for crops important in the global market (electronic supplementary material 2; right side). Single crops are crops directly listed with their production by the FAO and commodity crops are combined to a commodity with an aggregated production value.

Figure 2

Relative importance of animal pollination for the leading global crops and commodities used for human food and selected by their annual production in 2004. We considered crops and commodities with an annual production greater than 4 000 000 Metric tonnes (Mt) as these comprise 99% of the 2004 total crop production listed for human food. The number of crops and the production are listed according to their production increase with pollinators (see electronic supplementary material 1 for details). Single crops and commodity crops in NES^* commodities are separated. The category ‘unknown’ includes only commodity crops for the number of crops while the ‘unknown’ production is the production of the leading commodities, as the production value of each commodity crop is not known. Crops in the ‘increase’ category could be classified into three sub-categories with the following number of species and total production figure for the individual crops: production increase with pollinators for plant parts that we consume (fruits and/or seeds: 26 crops with 12 108 Mt=55%); increase in seed production with pollinators to produce the vegetative parts that we consume (six crops with 2108 Mt=9%); and increase in seed production with animals for breeding alone, as the plants reproduce vegetatively and we consume the vegetative parts (seven crops with 8108 Mt=36%). NES^* is an abbreviation for not elsewhere specified; leading commodities are fresh vegetables NES, fresh fruits NES, fresh tropical fruits NES, roots and tubers NES and pulses NES. Commodity crops are included based on a questionnaire that countries fill out to include important crops for the world market which are not listed as single crops.

Figure 3

Level of dependence on animal-mediated pollination. The selected crops are those included directly in the production list published by the FAO for 2004 (FAOSTAT 2005). We further included commodity crops for which the production was pooled in commodities with an annual 2004 commodity production greater than 4 000 000 Metric tonnes (Mt). Only crops that produce fruits or seeds for direct human use as food were considered. We did not include: (i) crops for which seeds are only used for breeding or to grow vegetable parts for direct human use or for forage, and (ii) crops known to be only wind-pollinated, passively self-pollinated or reproduced vegetatively. Essential, pollinators essential for most varieties (production reduction by 90% more, comparing experiments with and without animal pollinators); high, animal pollinators are extreme (40 to less than 90% reduction); modest, animal pollinators are clearly beneficial (10 to less than 40% reduction); little, some evidence suggests that animal pollinators are beneficial (greater than 0 to less than 10% reduction); no increase, no production increase with animal-mediated pollination; unknown, empirical studies are missing.

Figure 4

Expected relationship between the loss of animal-mediated crop pollination function (pollination variable usually measured as fruit or seed set in pollination studies and the variation usually measured as the coefficient of variation in the number or yield of fruits indicating crop production stability) and the effect of isolation from near-natural habitats (which means the area and distance of the main nesting and foraging habitats for the pollinators). Expected relationships in the absence of pollinator introduction are given for crops which are independent of animal pollination and for crops depending on animal pollination. Mean, solid line; variation, dashed line.