What is an example of a changing biotic factor?

One example would be the number of predators present in an ecosystem because say for example there is a pond or lake of fish as the prey, and a vast majority of bears as the predators, the bears can easily decrease themselves by leaving the ecosystem or by passing away by being killed or hunted, and even increase the majority by reproducing or decrease the population of prey by consuming most of them and outnumber the prey with more predators.

The offspring will be blood type aa, bb, ab and oo or i