What is one difference between a fundamental niche and a realized niche

Fundamental niche is the job/role that one species can have in the environment .
The realized niche is the role of a species influenced by several factors in the environment.
Example:
The fundamental niche of Yellow Warblers is found in a spruce tree.
The realized niche of the Yellow warblers is when they are "forced" to share the spruce tree and remain in one particular area of the tree while other warbler species play defense different niches in other parts of the tree.

:v it is like :
•Fundamental niche: [yellow warbler] "I got my home, all for me..."
~new species arrive to the spruce tree~
•Realized niche: [yellow warbler] oh, shoot! I gotta stay in the upper part/move to the upper part as the others warbler "struggle" to get territory :v or they just choose their own . :v