It depends on the type of change, if it is environmental, let's say that a new predator was introduced into an ecosystem, the ecosystem would certainly see some figures of animals decrease.
Deforestation is an example of a human cause of disruption to an ecosystem. Deforestation can destroy habitats which, of course, decreases amount of specific animals as sometimes we even burn trees from the rain forest.
Another human cause includes human waste. Our waste can make ecosystems unbalanced.
For negative impacts to be minimised, we must stop things like deforestation and care more for the ecosystems and the environment.
I hope this helps.