Understanding the place of humans in the global food chain

As concern increases about the ability of the earth to provide enough food for a growing human population it becomes increasingly important to better understand the feeding habits of humans. Recent research presents previously unknown information about our place in the global food chain.

Researchers in France have determined the Human Trophic Level and have found that, globally, humans are slowly moving to a diet which includes more meat, though this trend is not true in all countries. As the researchers explain, trophic levels describe the position of species in a food web, from primary producers to apex predators. They are regarded as critical for synthesizing species’ diets, depicting energy pathways, understanding food web dynamics and ecosystem functioning, and monitoring ecosystem health.

Among some of the interesting findings of the research:

  • humans currently appropriate 25% of the net primary production of the planet through food production and land use and this human appropriation is approaching the planetary boundary.
  • for a fixed quantity of food consumed, it is more efficient for human populations to eat from lower trophic levels (biomass rather than meat) to reduce the extraction of resources.
  • the global median human trophic level has increased by 3% since 1961. This trend is mainly driven by China and India and the human trophic level of the rest of the world is relatively stable.
  • there are large variations in diet between countries and over time.
  • in the global food web humans are similar to anchovy and pigs and cannot be considered apex (top of the food chain) predators.

There is considerable diversity in diet between the 176 countries of this study, but only five different groups of HTLs. The majority of sub-Saharan countries and most of Southeast Asia have a pattern of low and stable HTL, reflecting diets that are primarily plant based. Low and increasing HTLs are found for several countries throughout Asia, Africa, and South America, including China and India. Central America, Brazil, Chile, Southern Europe, several African countries, and Japan, have higher HTLs and also show an increasing trend. North America, Northern and Eastern Europe, Australia, and New Zealand, had high and stable HTLs until 1990, when they begin to decrease. Iceland, Scandinavia, Mongolia, and Mauritania, with traditional diets of meat, fish, or dairy products and low vegetable consumption, have the highest overall HTLs but these too are decreasing.

The research finds complex associations between HTL and the socioeconomic, environmental, and cultural characteristics of countries. Large-scale patterns show that HTL is positively related to, for example, gross domestic product, life expectancy, CO2 emissions, and urbanization rate, until a point after which the relationships plateau and then turn negative (declining consumption of meat).

The research paper is available, free abstract and small fee required for the full paper, in Proceedings of the National Academy of Sciences of the United States of America
at http://www.pnas.org/gca?allch=&submit=Go&gca=pnas%3B1305827110v1

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