Both plant and animal populations expand to the limit of the available resources. Algae on a pond surface does not get smart partway through the summer and say "Hold on lads! If we eat all the nutrients now we won't have enough for next month. Let's stop reproducing for a few weeks and keep ourselves at a nice stable population. We can gradually resume reproducing once we establish what the natural death rate is. That way we can go on forever." Squirrels have "learned" to put away acorns for later, but it is an instinctive response, not a reasoned one. They don't say "This was a great year for acorns and we're all fat and able to reproduce, but let's be cautious. There might not be so many acorns next year, and then our children will be hungry, or get killed by cars or other predators because they have to take increased risks to find food."
Human beings have done much the same until quite recently, and still do in some places. Populations expand because they can. They often do not expand to the level where just about everyone is comfortable, then call a halt. They expand to the maximum number that can survive and reproduce, even if just barely, given the available resources. That the human population has expanded hugely over the last two centuries is testament to great improved resources because of greatly improved technology. That hundreds of millions were hungry in Asia - and now Africa - is, paradoxically, a result of more resources, not fewer. It was not a distribution problem in the usual sense. It was an ever-increasing supply of acorns leading to more squirrels, with most of the squirrels just barely getting by.
This is what makes the lifting of so many from abject poverty in the last seventy, especially the last thirty years so remarkable. We are now providing food and curing/preventing disease at a faster rate than the population is growing.