Concept:Ecological niche means the total role of an organism in its habitat, so the factor that decides it is competition for shared resources.
Explanation:A niche is not just a habitat; it includes what an organism eats, when it feeds, and its relationships with other organisms.
Abiotic factors such as water, light, and temperature are part of the environment.
However, these conditions do not define the niche as strongly as biological interactions do.
The most important biological interaction is competition, which occurs when organisms need the same limited resources.
Food and living space are two basic resources for which organisms compete strongly.
This contest determines whether a species survives, how it feeds, and where it lives in the ecosystem.
Therefore, the factor that most influences an organism's ecological niche is the competition for food and space.
Answer:D. competition for food and space