Dear Andrei

A lot of questions!

As a start: a habitat is the combination of environmental characteristics of a species. A material thing.

A niche is the combination of species characteristics enabling it to live in its environment. It is about functional relations with its environment.

You may compare a species' habitat with an address and the niche with its profession.

I hope this may help, eager to read additional reactions!

Dear Andrei,

Agree with Godfried, a lot of questions. 

Here is Chapin III et al.'s definition of niche: ecological role of an organism in an ecosystem. 

From that definition, the concepts needed to define niche would be organismal (e.g., species) and ecosystem (e.g., habitat). The role (or profession) might then be described as how that organism fits within the overview trophic structure of that particular ecosystem. The limits of niche would therefore be the points of material transfer within the trophic structure beyond which the organism cannot successfully occupy. This is my understanding via Chappin III et al. 2002 Principles of Terrestrial Ecosystem Ecology, which coincides well with Godfried's description. 

As for the rest, I think you answer some of your own questions- if changes in trophic structure (or habitat) causes species composition to change, there technically aren't vacancies (i.e., empty rooms), unless that vacancy arose without a change in the underlying structure. Habitats do change (e.g., anthropomorphic land use change; ecosystem succession), therefore niches change. Delimiting would occur where the most limiting factor of the trophic structure is increased, allowing the system to reach an increased productivity/connectivity.

With all of that said, I think your definition makes a lot of sense. I likewise look forward to additional reactions from folks who know a lot more about this than I do (these are just some recollections/connections from graduate school). 

Sincerely, Ben

Dear  Andrei,

I think so. Now there is a need to perform falsifications in both the hutchinsonbian and grinnellian context, and develop theoretical models.

Sincerely

As far as I know, the problem of niche definition is not solved, but the focus of the debate -- as far as evolutionary mechanisms are concerned -- has moved more on the process of niche construction (see Laland's and Odling-Smee's works).

Dar Andrei,

I suggest you a different approach.

Please, think for ecological niche only as a THEORETICAL MODEL which only help you to understand ecological processes. Never think for niche as real think (something to measure or something to catch or something to exhibit).

Is it make sense?

Waiting for your kind feedback.

Attila

I asked a similar question some time ago. Answers were not very helpful. My position so far: the use of "habitat", "niche" and/or "community" mostly have no added value. The concepts need to be defined by the same set of attributes to be scientific. For example, if "habitat" is an address, geographical coordinates would be sufficient for point locations. What is "niche" more than a set of environmental variables or values thereof? Is a community a polygon rather than a point location?

Hello Andrei,

While I agree that an exact definition of a niche is still very much up for debate, apart from thinking in terms of the conventional definition of a niche as the ecological role of an organism in its ecosystem, another way a niche can be defined is that it is the set of environmental factors that allows a given population or species to sustain itself.

My understanding from Molles 2016 Ecology: Concepts and Applications (7th ed.) is that the full range of environments a species can inhabit comprises its fundamental niche while the more often limited environment a species actually inhabits is its realized niche. So with regards to one of your questions, it is possible to talk of an ecological niche even in an extreme situation wherein there may only be one living species. A fundamental niche would be more likely to be limited by abiotic factors and overall resource availability while the realized niche is limited by and often the result of competition between organisms possibly leading to competitive exclusion. However, some species may still be able to inhabit the entirety of their fundamental niche if the competition pressure restricting them to their realized niche is considerably reduced.

Ultimately, I would maintain that a niche is more of a feature of the environment, however, organisms are still important factors in determining how a given niche is partitioned.

Hope this was able to help!