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 speed of  sound:   sound travels  at different speeds depending on what it istraveling through. of the three mediums (gas, liquid, and solid)  sound waves travel the slowest through  gases, faster  through  liquids, and fastest  through  solids.