Describe a reason that ecosystem stability is important to the life forms in the ecosystem, and then describe why stability in one ecosystem is important for stability in an adjoining one

Different life forms adapt to their environment. Stable ecosystem creates a stable environment for life forms. In stable environment, life forms do not have to adapt all the time and their energy can be invested into other life processes, such as growth, reproduction, etc. Stability of ecosystem is important for adjoining ecosystems because that way boundaries and influences could be extended. Stable ecosystems are able to interact and both benefit from each other.

That would be a working theory.