In conversation with a vegan friend the other day, it came up that she would feel bad about eating meat, since it takes so much more land area under cultivation to produce beef than grain. She said four times. She felt that by eating meat she would be depriving other people of food.
I presume that by this she meant "The area sufficient to sustain one human life if that human were to live exclusively on meat could sustain four humans should they live entirely on wheat".
Obviously this is a somewhat meaningless statement, since either diet would kill you! I also have no idea whether it's true. But let's run with it for a bit. More rigorous versions can probably be concocted if necessary.
She probably also meant to say "And for at least some parts of the world, the limit on population growth is food supply". After all, if nobody's short of food, what is she feeling guilty about?
Our planet has a finite amount of farmable land area. Therefore, if population were to be restricted by food supply, the population would be four times greater if we were all vegans than if we were all meat eaters.
On the farmable land, there would either be lots of farm animals in the meat eating case, and none whatsoever in the vegan case (vegans don't exploit animals in any way).
Obviously in neither case would there be any room left for wild animals or plants on the farmable land. So the remaining wild creatures would have about the same land area left to them in either case (the bit we haven't worked out how to exploit yet).
But there'd be four times as much pollution and that would have amplified consequences in the vegan world. There'd be higher greenhouse effect , more poisoning of ecosystem, and so on. This might well have bad consequences for both the animals and the people.
So the vegan world would have many fewer farmed and wild animals, probably of many fewer types than the meat eating world.
I think domestic pets would probably have been 'phased out' in either case. When children are short of food, dogs and cats aren't likely to be a priority for many people.
The only sort of animal I can see doing better in the vegan world would be the various pest species.
Lots more humans and lots more grain in the world probably means vast numbers of rats and cockroaches.
Maybe that's what she meant. She claimed to like animals. I didn't get the feeling that her veganism was a plot to destroy them or anything.