One change in a population can affect a whole
If the rabbit population catch a diseases and the predator eat the infected rabbits they will catch the diseases get sick and die so will the rabbits and that will be a domino effect on the whole ecosystem
Carrying capacity is the maximum population an ecosystem can support
The carrying capacity of snow leopards is 35 in the snowy mountains
If a predator population increases prey population decreases
The hawk population increases and the mice decreases since its being hunted by priority since they are so many mice from overpopulation when the hawk population was low and couldn't eat so many mice.
If a prey population increases the predator population increases
If the gazelle population increases because it rained more than average so they ate more grass in turn the could feed more gazelle so they increased the population since the ecosystem could support more for the time being the predator being the lions have more gazelle to hunt so they can feed more lions in turn rising in population of lions.