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I’m having trouble figuring out what an unoccupied ecological niche is. I know what an ecological niche is, but what does it mean if it’s unoccupied?

1. what is an ecological niche ? give an ex?
2. describe six characteristics shared by all ecosystem?
3. how does energy move in ecosystem?
4. why doesn’t trash decompose in a modern landfill?
5. what is the ozone layer ? where is it located? why is it important to life on earth?
6. what is the ozone hole? how hav government responded to the discovery of the ozone hole?
7.why is ozone in the stratosphere considered beneficial whereas ozone at ground level is not?
8.what is acid rain? what steps would have to be taken to solve the acid rain problem?
9. why is the greenhouse effect a current areas of scientific concern when the earth has had carbon dioxide ,methane, and water vapor for several billion years?

pls help

I am stumped

a habitat is a portion of the real world
an ecological niche is a human perception describing how we perceive a species fits into the ecological categories it is related to or surrounded by

A niche is a particular place for a particular thing.