Global agricultural productivity is threatened by increasing pollinator dependence without a parallel increase in crop diversification

Abstract

The global increase in the proportion of land cultivated with pollinator-dependent crops implies increased reliance on pollination services. Yet agricultural practices themselves can profoundly affect pollinator supply and pollination. Extensive monocultures are associated with a limited pollinator supply and reduced pollination, whereas agricultural diversification can enhance both. Therefore, areas where agricultural diversity has increased, or at least been maintained, may better sustain high and more stable productivity of pollinator-dependent crops. Given that >80% of all crops depend, to varying extents, on insect pollination, a global increase in agricultural pollinator dependence over recent decades might have led to a concomitant increase in agricultural diversification. We evaluated whether an increase in the area of pollinator-dependent crops has indeed been associated with an increase in agricultural diversity, measured here as crop diversity, at the global, regional, and country scales for the period 1961-2016. Globally, results show a relatively weak and decelerating rise in agricultural diversity over time that was largely decoupled from the strong and continually increasing trend in agricultural dependency on pollinators. At regional and country levels, there was no consistent relationship between temporal changes in pollinator dependence and crop diversification. Instead, our results show heterogeneous responses in which increasing pollinator dependence for some countries and regions has been associated with either an increase or a decrease in agricultural diversity. Particularly worrisome is a rapid expansion of pollinator-dependent oilseed crops in several countries of the Americas and Asia that has resulted in a decrease in agricultural diversity. In these regions, reliance on pollinators is increasing, yet agricultural practices that undermine pollination services are expanding. Our analysis has thereby identified world regions of particular concern where environmentally damaging practices associated with large-scale, industrial agriculture threaten key ecosystem services that underlie productivity, in addition to other benefits provided by biodiversity.

Keywords: agricultural expansion; biodiversity; crop diversity; pollination; pollination services; pollinator-dependent crops.

Figure 1

Global change in total land area devoted to agriculture, agricultural pollinator dependence (estimated as the proportion of total agricultural area occupied by pollinator‐dependent crops), crop diversity (estimated as the effective number of crops), crop richness (i.e., number of crops), and evenness (estimated as Pielou's index) between 1961 and 2016, based on crop area data in the FAO dataset (FAOSTAT, 2018). For each dependent variable, x, change from 1961 until year t is represented as a percentage of the value of x in 1961, that is, 100 (x_t − x ₁₉₆₁)/x ₁₉₆₁

Figure 2

Least‐squares means (±1 SE) of growth in total agricultural area, agricultural pollinator dependence, and crop diversity, richness, and evenness for countries in each region of the world (i.e., AF, Africa; AM, America; AS, Asia; EU, Europe; OC, Oceania) between 1961 and 2016. Means with the same letter do not differ statistically at α = 0.05 according to a pairwise Tukey's a posteriori test. p‐Values correspond to the test for overall regional differences in each response variable (Table S1)

Figure 3

World maps of agriculture dependence on pollinators (i.e., the proportion of total cultivated area accounted for by pollinator‐dependent crops), crop diversity (estimated as the effective number of crops), crop richness (i.e., number of crops), and evenness (estimated as Pielou's index) in 1961 and 2016

Figure 4

Mean annual growth rates in crop diversity, richness, and evenness in relation to yearly growth rates in total agricultural area (left panels) and agricultural pollinator dependence (right panels) for 127 countries. Solid and dashed lines indicate significant (p < 0.05) and nonsignificant (p > 0.05) partial regressions, respectively. F‐test statistics are provided in Table S1

Figure 5

World maps of agricultural vulnerability through potential pollination shortfalls calculated as the difference between growth rates in agricultural area and crop diversity (Δ area vulnerability index) and between growth rates in agricultural pollinator dependence and crop diversity (Δ dependence vulnerability index) for 127 countries and former republics