On Sun, 08 Dec 2013 11:39:53 -0700, Bob Casanova <nos...@buzz.off>
wrote:
>On Sat, 07 Dec 2013 18:01:46 GMT, the following appeared in
>talk.origins, posted by Nick Roberts
><
tig...@orpheusinternet.co.uk>:
>
>>In message <
onh6a9p4l901u8qml...@4ax.com>
>> Richard Norman <
r_s_n...@comcast.net> wrote:
>>
>>[Snip]
>>
>>> 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?
In ecology, trophic levels are a very important idea because of the
flow of energy between levels: there is roughy 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
chemical substrates. We are familiar with these as "plants" and
"animals" but fungi are 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 they preys on owls who prey on mice who eat plants. Aquatic
ecosystems are very different because of the tiny size and abudance 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 indiscrimitately 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
abount of nutrition from aquatic carnivores. Even most hunter
gatherers don't many calories from eating terrestrial carnivores.
Since there are many organisms at trophic level 3 to 4, he 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.