Definition of Niche: the full range of biotic and abiotic conditions under which an organism lives. Because of competition and limited resources, organisms with similar requirements tend to sort into slightly different niches. Concept of competitive exclusion - two species will not occupy exactly the same niche.
The concept of the ecological niche is very important one; it helps us to understand how organisms in an ecosystem interact with each other. The concept is described by Odum as follows:
"The ecological niche of an organism depends not only on where it lives but also on what it does. By analogy, it may be said that the habitat is the organism's 'address', and the niche is its 'profession', biologically speaking."
Odum - Fundamentals of Ecology - W B Saunders 1959
What do oak trees do? If you can answer that question you know the oak trees "profession" or its ecological niche.
Perhaps you think that oak trees just stand there looking pretty and not doing very much, but in reality they do a lot.
1. absorb sunlight by photosynthesis;
2. absorb water and mineral salts from the soil;
3. provide shelter for many animals and other plants;
4. act as a support for creeping plants;
5. serve as a source of food for animals;
6. cover the ground with their dead leaves in the autumn.
These six things are the "profession" or ecological niche of the oak tree; you can think of it as being a kind of job description. If the oak trees were cut down or destroyed by fire or storms they would no longer be doing their job and this would have a disastrous effect on all the other organisms living in the same habitat.
Hedgehogs in a garden also have an ecological niche. They...