What are some possible effects of population growth?

In general terms, outrunning an organism's range. It uses up all the resources and the population then collapses, to then slowly rise again until it is once more outrunning its range. The population thus seesaws between overpopulation and near extinction.

Ecologically, this is prevented, and homeostasis is achieved by means of some variant of the predator prey relationship. The predator keeps the prey within limits, and the prey numbers limit the predators.

And here's the rub. We are a species that has outrun our range, and we have no predator prey relationship to achieve homeostasis, and this has very bad vibes for us.... Overpopulation causes overcrowded public transportation, traffic, faster spread of disease, higher unemployment rates, not enough food, rich government (ugh), and a lot more I hope someone else would add for me.