Who says so? Why would an observation that may (or may not) apply to bacteria or even to wolves apply to human beings?

Because it appears we're also DNA replicators.

But, let me play devil's advocate on your behalf, because I like your question. Let's assume that humans do realize their population problems and act to level growth, or reduce it. There's a strong argument that they would also act to reduce their resources, as well. Fewer people means less food necessary to feed the population; So why grow it?

We do have at least one significant difference from other species in our intelligence/self-awareness, but I challenge you to find any significantly large (compared to world population) group that acts even mostly out of rationality.

If a population stops growing, then clearly it's because it has run out of some resource, particularly if you go so far as to include things such as 'time' as a resource.

It also points out that it is the scarcest resource that limits growth. Increasing food will not allow the population grow if there isn't enough water, sun, etc.

My point was mostly to point out that we may have some other scarcity that isn't food which is limiting the growth rate in industrialized countries, while increasing the food in starving countries will just cause the population to grow until it hits the limit of some other resource.

I suspect that it isn't any sort of time scarcity that is limiting current human growth, but more likely the impact of contraceptives messing with our normal biological mechanisms.