Prof Richard Lewontin explains that organisms construct their environment as well as adapt to their environment. It’s been hypothesised that the evident good fit of an organism to its environment results from a combination of adaptation and environment construction. This is why Charles Darwin described organisms as fitting into a pre-existing niche in the environment.
In each organisms’ environment are other organisms (of the same species and other species). Richard Lewontin explains that the ecological niches within a habitat are dependent on the collection of organisms that inhabit it. In turn, the organisms themselves depend on the existence of the niches they occupy. So there are no pre-existing niches, just an environment crafted by many organisms interacting. This environment can and will change with organisms adapting to the environment and constructing their environment at the same time.
Prof Lewontin gives an explanation in his video lecture on Gene, Organism and Environment at 35 to 49 minutes (see below). An expanded version of the same material can be found in his book ‘The Triple Helix’.