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How much does agriculture depend on pollinators? Lessons from long-term trends in crop production - PubMed

How much does agriculture depend on pollinators? Lessons from long-term trends in crop production

Marcelo A Aizen et al. Ann Bot. 2009 Jun.

Abstract

Background and aims: Productivity of many crops benefits from the presence of pollinating insects, so a decline in pollinator abundance should compromise global agricultural production. Motivated by the lack of accurate estimates of the size of this threat, we quantified the effect of total loss of pollinators on global agricultural production and crop production diversity. The change in pollinator dependency over 46 years was also evaluated, considering the developed and developing world separately.

Methods: Using the extensive FAO dataset, yearly data were compiled for 1961-2006 on production and cultivated area of 87 important crops, which we classified into five categories of pollinator dependency. Based on measures of the aggregate effect of differential pollinator dependence, the consequences of a complete loss of pollinators in terms of reductions in total agricultural production and diversity were calculated. An estimate was also made of the increase in total cultivated area that would be required to compensate for the decrease in production of every single crop in the absence of pollinators.

Key results: The expected direct reduction in total agricultural production in the absence of animal pollination ranged from 3 to 8 %, with smaller impacts on agricultural production diversity. The percentage increase in cultivated area needed to compensate for these deficits was several times higher, particularly in the developing world, which comprises two-thirds of the land devoted to crop cultivation globally. Crops with lower yield growth tended to have undergone greater expansion in cultivated area. Agriculture has become more pollinator-dependent over time, and this trend is more pronounced in the developing than developed world.

Conclusions: We propose that pollination shortage will intensify demand for agricultural land, a trend that will be more pronounced in the developing world. This increasing pressure on supply of agricultural land could significantly contribute to global environmental change.

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Figures

Fig. 1.
Fig. 1.

Trends in total agricultural production and mean production deficits in the absence of animal pollination for the developed and developing world 1961–2006. The grey bands in the lower panels include the region delimited by the 2·5 and 97·5 percentiles of randomized distributions and depict uncertainty in the estimation of the production deficit.

Fig. 2.
Fig. 2.

Rank abundance curves of crops cultivated in the developed and developing world (upper panels). Crops were ranked from the most to the least abundant according to their total production in each region. Each crop was coded based on its pollinator dependence category (0–4). Crop names are not included for clarity. In the lower panels, crops were grouped according to their pollinator dependence categories and production data summarized as box plots. Sample sizes (i.e. number of crops) are given in parentheses. Note the logarithmic scale of the y-axis in both upper and lower panels.

Fig. 3.
Fig. 3.

Trends in crop diversity and expected mean diversity deficits in the absence of animal pollination for the developed and developing world 1961–2006. Diversity was estimated by Pielou's J and Hurlbert's PIE evenness indices. The grey bands in the lower panels include the regions delimited by the 2·5 and 97·5 percentiles of randomized distributions and depict uncertainty in the estimate of the diversity deficit.

Fig. 4.
Fig. 4.

Trends in total cultivated area and in the extra cultivated land required to compensate for the deficits in crop production in the absence of animal pollination (i.e. area compensation) for the developed and developing world 1961–2006. Area compensation was estimated assuming that the pollinator dependence of individual crops was represented by the mid-value of the range defining its corresponding dependence class (average-area compensation) and by the lower limit of that range (minimum-area compensation).

Fig. 5.
Fig. 5.

Associations of the average annual rates of growth in area (βΔarea), production (βΔproduction) and yield (βΔyield) for crops in the developed and developing world relative to values in 1961. Results of Spearman's correlations are provided.

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References

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