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| Human World on Dec 06, 2013

Humans aren’t top predators, says new report

Despite a global increase in meat consumption, humans are far from the top of the food chain.

Sorry fellow humans but, contrary to the popular idiom, we aren’t at “the top of the food chain.” It turns out we’re actually somewhere in middle. So says a 49-year analysis of human food consumption across 176 of the world’s 196 countries. The study marks the first time anyone took the trouble to calculate human trophic level – a measurement of a species’ position in the food web. While apex predators’ levels can go as high as 5.5, the global average trophic level for our species in 2009 was a piddling 2.21. That’s comparable to pigs and anchovies (the researchers’ examples), animals that are coincidentally also both popular pizza toppings (my commentary).

Sample food web. Image: US-Geological-Survey.

Sample food web. Image: US-Geological-Survey.

“Why so low?” you ask, “What about my Paleo/Atkins/T-Rex Burger diet? Shouldn’t I at least be a 3?” To explain why the answer is no, let’s look at how trophic level is determined. The general range is 1 to 5. Plants (and other “primary producers”) are a 1; they make their own food and, excluding the handful of carnivorous species, they don’t eat anyone else. For the rest of us, our level is calculated as 1 plus a weighted average of the trophic levels of whatever it is we eat. So an animal that eats exclusively plants (e.g., cows, vegans) would have a trophic level of 2, whereas something that subsisted on a 50/50 split of plants and cows (or plants and vegans, if you prefer) would score a 2.5*. Species with the highest trophic levels are not just carnivores, they’re carnivores that eat other carnivores. Humans, being omnivores, will have a hard time matching that kind of consumption. But if we were determined to climb the trophic ladder, we might want to dispense with cows altogether and focus on eating things like lions and bald eagles. Before we get all competitive though, let’s explore why doing so would be a terrible idea.

While it’s good novel fun to strip homo sapiens of its illegitimate title of apex predator, the purpose of the study wasn’t just to provide scientists with another opportunity to correct laypeople in conversation. Calculating the human trophic level (HTL) allows us to better understand our species’ impact on ecosystems and the planet’s resources. All the plants in the world can only produce so much energy (aka food), and some of this energy is lost at each stage as it travels through the food web. In terms of efficiency, more plants are required to provide a population with an all cow diet than with an all plant diet. An all Bengal tiger diet would, of course, be even more energetically costly (plus they’re endangered, you monster, can’t you just accept your 2.21 and move on?)

At this point I should mention that the 2009 average HTL is up by 3% from the 1961 figure. Considering the energetic costs of dining at higher trophic levels, the better question about that 2.21 might now be, “why so high?” The main reason is volume. As a species, we aren’t really eating animals with higher trophic levels, we’re simply eating more meat (and animal products) overall. But that’s as a global average. When broken down by nations, the range in 2009 HTLs was quite broad – from Burundi’s almost vegan 2.04 to Iceland’s meat-o-centric 2.57 (cut them some slack, it’s hard to grow vegetables near the Arctic Circle).

Looking at change in HTLs over time, the study found five patterns:

1) low and stable (comprised of countries in sub-Saharan Africa and Southeast Asia)

2) low but increasing

3) higher and increasing

4) high and fairly stable (the U.S. is in this group)

5) high but decreasing (including Iceland…hey, they’re trying)

Herbivore meat, only worth 2 points. Image: Helga's Lobster Stew

Herbivore meat, only worth 2 points. Image: Helga’s Lobster Stew

Among the low-but-increasing group 2 were China and India, which are driving that upward trend. But if you remove China and India from the analysis entirely, the 2009 global HTL actually goes up from 2.21 to 2.31, meaning that, while their increase in meat consumption is dramatic, those two nations are still hardly the most carnivorous of the lot.

All this shifting meat consumption is a concern because, despite our middling trophic level, we’re quite good at sucking up resources. According to the study, humans use 25% of the net primary production (that finite amount of planty energy we discussed earlier), and food production accounts for 35-40% of that allocation. Given that agriculture isn’t even our only drain on global resources, the fact that we’re not at the top of the food chain is probably a good thing.

* The dumbed down version of the math goes like this: (0.5*1 + 0.5*2) + 1 = 2.5, 1 being plants and 2 being cows. (The actual formula is uses sigma notation, which WordPress isn’t ready to deal with today.)