It's far more complex than this. A lot of meat --free-range cattle and sheep particularly--is raised on land which is not arable for traditional crops. Farmed fish too, when farmed responsibly, can provide a lot of food on "land" which could not have produced other food.

But we aren't lacking land to grow food. We have so much of it actually that we use a third of the arable land world wide to grow feed for livestock, (which accounts for 40% all grains grown)[1]. If we just ate this grain instead we could feed 3.5 billions people extra[2].

Cattle (and sheep) are extremely inefficient. We use 60% of all farmland to produce beef, but it only provides us with 2% of all calories (5% of protein)[1]. So, the majority of all pastureland plus a big chunk of the arable land is used to produce 2% of all calories. That's not really much of a resource.

So yes, if we raised cattle purely on pasture (which we don't overall) we could actually get some net production of food. But it would still be an insignificant part of our diet.

[1] Grade A Choice? Solutions for Deforestation-free Meat. Union of Concerned Scientists, 2012: http://www.ucsusa.org/assets/documents/global_warming/Soluti...

[2] Meat and Animal Feed: http://www.globalagriculture.org/report-topics/meat-and-anim...

One issue is that arable land isn't, along with other resources, evenly distributed over the plant, nor do the people have equal access to technology maximise production output.

This is why we need trade, which is arguably better than one form or another of centralised government controlled redistribution.

So the issue isn't, and probably never will be, limits to resources, but limits to human resourcefulness - of which there are none.

As far as I'm aware, fish are fairly land efficient.

But not resource efficient, and farmed fish have lots of problems.