What ecological principle states that no two species can occupy the same exact niche simultaneously?

The correct answer is the competitive exclusion principle, which is a fundamental concept in ecology that asserts that two species competing for the same resources cannot coexist in the same niche over time. This principle is based on the idea that if two species are competing for identical resources, one species will inevitably outcompete the other, leading to the local extinction of the less competitive species or forcing it to adapt to a different ecological niche.

This principle is essential in understanding the dynamics of species interactions and the structure of biological communities. It helps explain the distribution and abundance of species in ecosystems, illustrating how competition shapes community composition and biodiversity. The competitive exclusion principle emphasizes the importance of resource availability and how it influences the survival and reproduction of species sharing similar ecological roles.

The other options relate to ecological concepts but do not directly define the interaction described in the question. Population gradient theory concerns variations in species populations in relation to environmental gradients. Niche differentiation rule pertains to how similar species can coexist by utilizing different resources or habitats. Resource partitioning involves how different species use resources in varied ways to minimize competition, but it does not specifically state the limitations imposed by niche overlap as the competitive exclusion principle does.