Which statement is true about the relationship between a species' fundamental and realized niches?

• A. Realized niche is always larger than fundamental
• B. They are identical in all communities
• C. The realized niche is the portion of the fundamental niche actually occupied
• D. The fundamental niche cannot be defined without considering biotic interactions

Answer: (C)

Understanding how a species uses space in an ecosystem hinges on two ideas: the potential range of conditions a species can tolerate (its fundamental niche) and the actual range it occupies in a community (its realized niche). The fundamental niche reflects abiotic tolerances and resources a species could use if there were no biotic constraints. The realized niche is the subset of that potential range where the species actually lives, after accounting for interactions with other organisms such as competition, predators, and mutualists. Because these biotic factors often limit where a species can persist, the realized niche is usually smaller than the fundamental niche, and can sometimes be equal if biotic pressures are weak.

So the statement that the realized niche is the portion of the fundamental niche actually occupied is the correct one. The other options don’t fit this relationship: the realized niche is not typically larger than the fundamental, they are not identical in all communities due to biotic interactions, and the fundamental niche is defined largely by abiotic conditions and can be considered without invoking biotic interactions.