a, Black dots are mean effective crop species diversities and bars show the σ for nations grouped as planting 1–20, 20–40, 40–60, 60–80 or 80–100 crop species during 2001–2010 (n = 91). Data for each nation are shown as grey dots. Note that for a given number of crop species, there is a wide range in their effective crop species diversity caused by some nations having only a few dominant crops (and thus having a low effective diversity) and other nations having many crops of more similar abundances (and thus a high effective diversity). The two circled dots highlight 2 such nations, both growing 30 crop species but either very unevenly (that is, the dot with low effective diversity) or more evenly (that is, the dot high effective diversity). b, The frequency distribution of the effective crop species diversity values for this same time period.