The process where one species evolves to fill the ecological niche of another is called niche differentiation or character displacement. This phenomenon occurs when competing species adapt their traits or behaviors to reduce competition for the same resources in an ecosystem. Over time, natural selection may favor different adaptations in these species, allowing them to coexist despite their overlapping niches. Niche differentiation is vital for promoting biodiversity and ecological stability. Understanding this process helps ecologists predict how species interactions shape community structures and ecosystem dynamics.