Final answer:
The population size of a species is not included in its niche.
Step-by-step explanation:
The answer is D. the population size of that species.
A niche refers to the role of a species in its ecosystem, and it includes all the ways that the species interacts with the biotic and abiotic factors of the environment. The population size of a species is not considered a part of its niche because it does not directly relate to the species' functional role in the ecosystem or its interactions with other factors.