[jamesqf]

Originally Posted by IamIan

And for any size meat intensive eating population you pick .. that will consume more resources than a equal sized Vegetarian or Vegan Population.

I don't want to write a book here, but seems to me that if you are going to have a sustainable system, you simply can't think in terms of 'consume' and 'resources'.

and that same total amount of resources could just as sustainably feed a larger population of Vegetarian / Vegans... because every 1 meat calorie requires several times that input plant calories.

Not true - or rather, true only in a very limited sense, where you just measure energy input and outputs in isolation. If you think instead of entire systems, you might see that those 'meat calories' are actually doing some pretty important things in the ecosystem on their way to becoming calories. If you don't have them performing their functions naturally, you have to replace them with external inputs like chemical fertilizers, plowing, hand pollination, &c, all of which are necessary to make the system sustainable.

... every 1 meat calorie output (for a meat eater to eat) ... requires several times that more calories input (as plant calories) to get it... it is horribly low efficiency.

But those calories are, in most cases, being gathered from sources that humans can't utilize directly. For one simple example, humans can eat only a small part of grain plants such as wheat or corn. Grazing animals can eat the whole plant, and turn any excess into fertilizer to boot, as well as providing numerous other ecosystem services.

For a different argument, we might step back a bit and ask why, if meat-eating (or carnivory/predation in general) is so inefficient, it persists despite several hundred million years of evolutionary pressure to eliminate inefficiency?

I was trying to point out that just because an ecosystem is degrading is not enough on it's own to make the leap you were making about the sustainability of the global human population... An Ecosystem can degrade for a wide variety of reasons .. the effects of a large human population is not the only potential cause.

Certainly - but we find numerous examples that ARE caused by the activities of large human populations, it seems fair to hypothesize that such effects are inescapable, and so peg our maximum sustainable population at a level where the effects are not significant. Of course if it could be demonstrated that the effects could be eliminated somehow, that would change, but AFAIK that can't be done.

But we are also not talking about low impact population ... or a zero impact population ..

But that's my argument: unless & until ecology becomes an exact engineering discipline, a sustainable population has to be low or zero impact, otherwise the impacts eventually cause the system to collapse.

PS: Quite by coincidence, I just happened on an interesting example of those unconsidered ecosystem services: the effect of insects in urban garbage removal: http://news.sciencemag.org/biology/2...rash-each-year