Keystone species are critical in maintaining balance in ecosystems due to their disproportionately large impact on their environment compared to their biomass. They regulate populations of other species, which can prevent any one species from dominating and ensure a diversity of organisms within an ecosystem. The presence or absence of a keystone species can significantly alter species composition and ecosystem structure. Protecting these species is essential for preserving ecological processes and biodiversity, as they contribute to the functionality and stability of their ecosystems.