The term "keystone species" refers to species that have a disproportionately large impact on their ecosystem relative to their abundance. These species help maintain the structure and function of the ecological community. For example, predators, such as wolves or sea otters, can regulate the populations of prey species, which in turn influences plant communities and overall biodiversity. The removal of a keystone species can lead to significant ecological imbalances and loss of biodiversity, making their conservation critical for ecological health.