A population's growth can rely on the factor of competition.
The competition against a specific food or water source has been common between species before. If they can't find another food or water source, they are going to being dying (basic fact). Basically, this is where "strongest survive" theory comes into play. If a species can't have a meal because another species has already claimed it, that family may begin to die if they can't eat.
Let's create a fake scenario here to clear it up:
A species of animal (A) is fighting another species (B) for their food (C).
A is stronger than B, and A seems to be lowering B's available food quantity when B go hunting. Eventually, species A will either begin to kill off B due to lack of food, or A will force B to move into another area, sometimes even a different biome. B's population growth is forced to slow down because they won't have food to feed their offspring.
My apologies if I made that harder than it needs to be.
Hope I could help you out! Have a good one.
God bless.
