, certain key species are essential because they drive major ecosystem functions . This concept is illustrated by the 'rivet popper hypothesis', which suggests that the loss of these specific species poses a far more serious threat to the stability and functioning of the environment than the loss of others . Furthermore, the sources note that some species help maintain species diversity in a community by reducing the intensity of competition among other species, thereby controlling their relative abundance . While the sources use the term 'key species,' the term keystone species in the options refers to this functional role. In contrast, alien species are non-native organisms that may become invasive , and endemic species are those confined strictly to a specific geographical region .