What causes ecosystems to change over time?

Many things can cause change in ecosystem. These include habitat destruction for human builds, Introducing new species to a ecosystem that are not part of the food chain, Poaching, and even most pestacides can cause severe change to an ecosystem. Food chain disturbance example: Lionfish. They were somehow introduced by being let out of an aquarioum. These exotic fish are disturbing the food chain and causing many different other species of fish like grouper to have no food to eat.