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Describing humans as apex predators: misleading, wrong or impure?

Post of the Month: December 2013


Subject:    | Humans are not apex predators
Date:       | 08 Dec 2013
Message-ID: |

Following a post about an article on the place of humans in the food web, the discussion evolves toward the meaning of "apex predator":

>>> The subject is not at all whether humans are destroying the ecosystem. And
>>> the paper is not at all an apologetic for that destruction. The simple fact
>>> is that the human diet in no way shape or form resembles the diet of an apex
>>> predator.

>> I've not had any training in ecology, but it struck me while reading this
>> thread that pre-agriculture humans may indeed be apex predators. Would this
>> be accurate?

>> If so, humans may be in the unique position of being an ex apex predator, not
>> because a different species got better at predation, but for social reasons.

> Quite a few of the comments I've read in this thread seem to assume that an
> apex predator (in fact, a predator in general) is necessarily a carnivore.
> This doesn't seem to square with the definition of "predator" ("an animal
> which preys on others"), which only seems to exclude herbivores; bears and
> humans are both predators, and I'd consider both to be candidate apex
> predators. Comments?

Richard Norman's POTM presents a more realistic model:
In ecology, trophic levels are a very important idea because of the flow of energy between levels: there is roughly a 90% "loss" between levels, only 10% of the caloric content of one level being made available to the next higher level feeding on them. I put "loss" in quotes because that energy is lost only in terms of producing new biomass. It really is used to carry out the functions of life and to reproduce which are certainly not losses in the more general sense.

The important terms in ecology are producers; making biomass from inorganic substances and using external sources of energy, mostly sunlight and consumers; feeding on other organisms for energy and the organic material to build their own biomass. We are familiar with these as "plants" and "animals" but fungi are also consumers. There are both consumers and producers in the microbe world. In turn, consumers can be first order (eating producers), second order (eating first order consumers), and so on. In terrestrial habitats, the "top level" trophic level is usually a tertiary consumer, something that eats not just carnivores but carnivores that themselves feed on carnivores. An example would be a hawk that preys on owls who prey on mice who eat plants. Aquatic ecosystems are very different because of the tiny size and abundance of the usual planktonic producers. This allows for a wide variety of invertebrate herbivores, also tiny, to be eaten by fish who are then eaten by bigger fish and so on. So there tend to be more trophic levels in aquatic systems although the limiting energetics still keeps the chain rather short.

It is quite obvious that there are many carnivores who feed at more than one trophic level. That is why there is a food "web" rather than a simple food "chain" or ladder of levels. You can readily compute an "effective trophic level" as a weighted average of feeding. If 40% of your food comes from level 1 (plants) and 60% from level 2 (herbivores), then you are at trophic level 1.4. That is exactly the notion of trophic level used in the paper.

I do all this because those are the important "pure" concepts. Then there are terms whose usage is sometimes variable, terms like "predation" and "apex predator". Ordinarily predation means feeding on animals. Grazing and parasitism are means of "preying" on others but are considered different. Even herbivores that kill the plants they eat are not ordinarily considered to be predators. Sometimes even predation, selectively seeking out which organisms to eat, is separated from filter feeding where you indiscriminately eat everything you manage to catch.

Apex predator merges two concepts, sometimes applied with different force by different users for different purposes. One is that the apex predator is at the top of the food chain, the highest level consumer. Ordinarily that means that it is a tertiary or even a quaternary consumer on land. In marine systems it would ordinarily be a fifth level consumer. A second aspect is that the apex predator has no "natural enemies". That is, there is nothing that normally preys on it. Detritus feeding and scavenging already dead carcasses is a separate category.

Modern humans, as has been pointed out many times, have an effect on the ecosystem far in excess of simple trophic feeding. But to concentrate simply on feeding, our trophic level is somewhere between 2 and 3 meaning most populations do get a reasonable amount of nutrition from aquatic carnivores. Even most hunter gatherers don't obtain many calories from eating terrestrial carnivores. There are many organisms at trophic level 3 to 4, that don't qualify. Also, before the advent of modern technology (and still continuing today in many parts of the world) there are plenty of predators that regularly take humans as food. Again, we fail to qualify as unambiguous apex predators.

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