It's impossible to say definitively which is *not* a disturbance of an ecosystem without more context.

Here's why:

* Disturbances are a natural part of ecosystems: Ecosystems are dynamic, constantly changing systems. Disturbances, both natural and human-caused, are crucial for maintaining biodiversity and ecosystem health.

* Disturbance scales vary: A "disturbance" can be anything from a small tree falling in a forest to a massive wildfire or a human-caused oil spill.

To help me understand what you're asking, please tell me more about the context. For example:

* Are you looking at natural disturbances vs. human-caused disturbances?

* Are you thinking about specific types of ecosystems?

* Do you have a list of potential disturbances to choose from?

Once I have more information, I can give you a more helpful answer.