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

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.Environmental Biolog

On optimal nectar foraging by some tropical bees (Hymenoptera: Apidae)

Sugar concentration in nectar foraged by 13 Euglossini, 16 Meliponini and 8 Centridini (Apidae) was monitored in floristically rich habitats. For 6 Meliponini, sugar solution profitability by imbibement rate was compared to nectar choice (figs 1-4, tables I-IV). In addition, foraging assays tested meliponine response to 10 amino acid solutions (table V, fig 5). Optimal nectars were 35-65% sugar among bees, and apparently their modal forage. Bees also accepted suboptimal nectar, or were 'rate maximizers'. Two species had modes well below the means, indicating facultative selection of dilute nectars. For pollination, heterogeneity and optimal nectar sweetness are likely key mechanisms causing forager fidelity. Mean sugar contents were 38, 44 and 48 for Euglossini, Meliponini and Centridini, respectively; modes averaged 3-4% higher. All bees used nectars of 30-45% sugar; some also used nectars of 10-15 or 65-70% sugar; others did not use nectar of over 60% sugar. Amino acid solutions of 35-80 mM concentration did not generally affect attractiveness, but Melipona avoided glutamic acid, glycine, serine, alanine and proline, responding comparably to 20-40% sugar solutions contrasted with 50% concentration