In ecology, this is the “job” or role an organism plays in its community. A description of a niche will include the plants, animals and other living things an organism interacts with. But all the parts of an organism’s life are part of its niche — where it lives, what it eats and what eats it. When a fox preys on a rabbit, the fox’s niche is predator. The rabbit’s niche is prey. The hole in the ground the fox calls home is also part of its niche. If the fox has fleas, then part of its niche involves being a host to those parasites. Every organism in a community — from a forest to a cave to the ocean to your own belly button — has its own niche.
In a sentence
Dinosaurs may have taken advantage of a big extinction event to take over many niches left open in the environment.