Final answer:
An organism's realized niche is indeed typically smaller than its fundamental niche due to competition and interaction with other species, which limits its range of conditions and resources actually used.
Step-by-step explanation:
The statement that an organism's realized niche is always smaller than its fundamental niche is true. The fundamental niche represents the full range of environmental conditions and resources an organism can potentially use, without the influence of competition or other species.
In contrast, the realized niche is the actual set of conditions and resources it uses in the presence of competition and interactions with other species, which naturally limits its range. Therefore, due to these biotic constraints, an organism's realized niche is typically smaller than its fundamental niche.