Abstract
The Anthropocene epoch is partly defined by anthropogenic spread of crops beyond their centres of origin. At global scales, evidence indicates that species-level taxonomic diversity of crops being cultivated on large-scale agricultural lands has increased linearly over the past 50 years. Yet environmental and socio-economic differences support expectations that temporal changes in crop diversity vary across regions. Ecological theory also suggests that changes in crop taxonomic diversity may not necessarily reflect changes in the evolutionary diversity of crops. We used data from the Food and Agricultural Organization (FAO) of the United Nations to assess changes in crop taxonomic- and phylogenetic diversity across 22 subcontinental-scale regions from 1961–2014. We document certain broad consistencies across nearly all regions: i) little change in crop diversity from 1961 through to the late 1970s; followed by ii) a 10-year period of sharp diversification through the early 1980s; followed by iii) a “levelling-off” of crop diversification beginning in the early 1990s. However, the specific onset and duration of these distinct periods differs significantly across regions and are unrelated to agricultural expansion, indicating that unique policy or environmental conditions influence the crops being grown within a given region. Additionally, while the 1970s and 1980s are defined by region-scale increases in crop diversity this period marks the increasing dominance of a small number of crop species and lineages; a trend resulting in detectable increases in the similarity of crops being grown across regions. Broad similarities in the species-level taxonomic and phylogenetic diversity of crops being grown across regions, primarily at large industrial scales captured by FAO data, represent a unique feature of the Anthropocene epoch. Yet nuanced asymmetries in regional-scale trends suggest that environmental and socio-economic factors play a key role in shaping observed macro-ecological changes in the plant diversity on agricultural lands.
Highlights
A major line of scientific evidence defining the Anthropocene epoch–the period of Earth’s history defined by the dominance of humans–is the human-caused changes in Earth’s biodiversity and biogeography
Our analysis employed diversity metrics that relied on species-level taxonomy, by following a two-step process to identify the crop species associated with each commodity group. First, we used Food and Agricultural Organization (FAO) commodity group codes, in conjunction with the FAO Commodity List tool, to identify the crop species the FAO associates with each group (Table A in S1 File)
Major shifts in regional crop taxonomic diversity (measured as crop species richness (SR)) and phylogenetic diversity (PD), occurred within all regions in very similar patterns: i) a period of little change in diversity from the early- through to the late 1960s, followed by ii) a period of rapid increase in diversity beginning in the late 1970s through mid-1980s, which endured for ~9.5–10.5 years on average, which iii) stabilized in the early 1990s (Figs 1 and 2, Figs A and B and Tables C and D in S1 File)
Summary
A major line of scientific evidence defining the Anthropocene epoch–the period of Earth’s history defined by the dominance of humans–is the human-caused changes in Earth’s biodiversity and biogeography. Global-scale assessments of the changes in crop diversity over recent decades have largely reported linear increases in the crop diversity (and evenness) associated with global diets and agricultural economies, with these patterns being key for understanding trends in food production, consumption, and trade [3, 7,8,9]. Patterns of crop diversification have not been evaluated through regional comparisons of crop diversity change through time
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