Researchers calculate human trophic level for first time

Dec 03, 2013 by Bob Yirka report
. (A) Trends in the human trophic level (1961–2009) and (B) map of the median human trophic level over 2005–2009. Credit: (c) PNAS, Published online before print December 2, 2013, doi: 10.1073/pnas.1305827110

(Phys.org) —A team of researchers in France, has, for the first time, calculated the Human Trophic Level (HTL)—a number that indicates the proportion of the diet as it relates to the food chain. In their paper, published in Proceedings of the National Academy of Sciences, the researches describe their efforts to combine demography, ecological impacts and socioeconomics to determine the HTL for various groups living around the world, which led them to calculating a worldwide global average.

We human beings like to think of ourselves as living at the top of the —doing so implies we have dominion over all the other plants and animals living on this planet. And while that implied perspective is perhaps correct in one sense, it's not when looked at in its truest biological sense. Organisms at the very top (apex) of the food chain eat only meat—the meat of other predators, that is. Organisms at the bottom, conversely, eat only simple plants. With that definition, in mind, we know we're not going to sit at the top—we eat lots of vegetables, thus we're not going to compete with the likes of tigers or crocodiles.

To put things in perspective, scientists have created a scale that allows for relative comparisons between species, it's called the trophic level and it runs from 1, for base level eaters, to an apex level of 5. What's perhaps most odd about the scale, though, is that nobody's ever thought to find the level for humans. Intrigued, the team in France set out to do just that.

To find out, the researchers turned to the Food and Agricultural Organization (FAO)—it's run by the U.N. and has extensive information regarding the eating habits of people throughout the world. They used the information they were provided to calculate HTL levels for people living in various parts of the world, and then came up with a worldwide average—it's 2.21, about the same as a pig, or an anchovy. That means that meat makes up less than half of our diet (that would be 2.5).

Of course there are variations, vegetarians, for example, would score much lower, whereas some people might subsist mostly on fish, fowl or red meat. Not surprisingly the data obtained by the researchers shows that the more advanced a country becomes, the more meat the people eat, until reaching a plateau.

Knowing the HTL for humans may not cause any changes in the way people eat, but it might just cause some to pause and reflect on our true place in the animal kingdom.

Explore further: How animals go from farm to fork in 24 hours

More information: Eating up the world's food web and the human trophic level, Published online before print December 2, 2013, DOI: 10.1073/pnas.1305827110

Abstract
Trophic levels are critical for synthesizing species' diets, depicting energy pathways, understanding food web dynamics and ecosystem functioning, and monitoring ecosystem health. Specifically, trophic levels describe the position of species in a food web, from primary producers to apex predators (range, 1–5). Small differences in trophic level can reflect large differences in diet. Although trophic levels are among the most basic information collected for animals in ecosystems, a human trophic level (HTL) has never been defined. Here, we find a global HTL of 2.21, i.e., the trophic level of anchoveta. This value has increased with time, consistent with the global trend toward diets higher in meat. National HTLs ranging between 2.04 and 2.57 reflect a broad diversity of diet, although cluster analysis of countries with similar dietary trends reveals only five major groups. We find significant links between socio-economic and environmental indicators and global dietary trends. We demonstrate that the HTL is a synthetic index to monitor human diets and provides a baseline to compare diets between countries.

Related Stories

Are crocodiles secret fruit-lovers?

Nov 12, 2013

Seed dispersal by animals is important for plants to help them occupy new areas of land. Usually bugs, birds, or intrepid kittens do that job. Now we can add crocodiles to that list. A new study reviewed ...

Smaller islands host shorter food chains

Nov 22, 2013

That smaller islands will typically sustain fewer species than large ones is a widespread pattern in nature. Now a team of researchers shows that smaller area will mean not only fewer species, but also shorter ...

Recommended for you

Zambia lifts ban on safari hunting

1 hour ago

Zambia has lifted a 20-month ban on safari hunting because it has lost too much revenue, but lions and leopards will remain protected, the government said Wednesday.

The devastating spread of the mountain pine beetle

8 hours ago

When the mountain pine beetle began blazing a path across forests in British Columbia and Alberta, nobody could have imagined the extent of the damage to come. But as the insect devastated pine forests and ...

User comments : 8

Adjust slider to filter visible comments by rank

Display comments: newest first

210
3 / 5 (2) Dec 03, 2013
Humans are overtly omnivorous, overtly. We compete for the richest food/energy sources nutritionally speaking. Cows, compete with us partially, mountain lions when they eat our pasteur-animals. Dogs are omnivorous by extension or after the fact; they ate the cow, and its partially digested stomach contents which were plant sourced - a common dietary balancing act in the Wild Kingdom (also Wall Street.) In fact, humans eat everything - go to France or China and look at a menu, OMG!!! The animal AND plant kingdoms see us coming and collectively wonder,"is there anybody's relatives the humans have not eaten?"
WE are the top culinary masters, now the bacteria are master omnivorists!

word-
FainAvis
not rated yet Dec 03, 2013
pasteur [sic] Did you mean pasture?
210
not rated yet Dec 03, 2013
pasteur [sic] Did you mean pasture?

Yes, I did indeed....it is bad enough to talk on the phone, or text, and drive. Writing comments on physorg MUST take preeminence. I shall not use more than two phones at the same time while making my submissions here, going forward. THAT will be my new year's resolution as well (ha ha)
word-
alfie_null
not rated yet Dec 04, 2013
I'd argue that the top of the food chain means not that you eat your potential competitors, but that you prevent them from competing with you.
pepe2907
3.7 / 5 (3) Dec 04, 2013
The whole idea about the food chain is quite incorrect - first of all - it's not chain at all /there's nobody /probably with the exception of some parasites/ who eats only somebody else specific/ - it's a pretty complicated net, and on top of that it's actually a circle - a circle of matter and energy, where even the organisms of the so called "apex" are occasionally completely or partially eaten by the simplest ones /bacteria and viruses, causing illness, killing cells of their bodies etc./, and eventually every living thing dies and is being eaten again by bacteria, worms... So, why not put the bacteria at the top?
So, the idea is not just "quite" incorrect, it's more like completely incorrect, and while it's OK for an average human to think in terms of "food chains" and "apex"-es, it looks for me as being quite much of oversimplification /if not something more/ when scientists think in those categories.
pepe2907
3.7 / 5 (3) Dec 04, 2013
This doesn't mean there's no such thing as Trophic Level, but it's not about how high in the food chain you are, but more as how big of a knot you are in the network of matter and energy redistribution - how much energy and matter goes through you. There's also a factor of how effectively do a specific organism utilize this energy, but there the tendence is pretty general, where the more complex organisms are usually less effective in utilizing it.
And also there's another thing - no organism is actually just one simple "thing" :) - complex organisms consist of multiple cells and in addition are populated by many different types of simpler ones participating on different levels of that pretty complex matter and energy redistribution net.
pepe2907
3 / 5 (2) Dec 04, 2013
Well, people who can't argue on an idea may still vote, don't they? :)
thingumbobesquire
1 / 5 (1) Dec 04, 2013
What places humanity absolutely above the "animal kingdom" is our creative ability to discover, control and utilize energy in ever more dense forms. Thus we alone as a species are able to use fire. Today we are on the brink of controlled thermonuclear fusion energy which will lead into matter anti matter forms even more dense. This creative power is not recognized by today's green propagandists and neo Aristotelians who religiously believe humans are but talking beasts.