English: keystone species
Welsh: rhywogaeth allweddol
Subject: Amaeth
English definition: A species whose addition to or loss from an ecosystem leads to major changes in abundance or occurrence of at least one other species.
Welsh definition: Er bod peth amwysedd ynghylch union ystyr technegol y gair, ei ddiffiniad mwya cyffredin yw rhywogaeth sy'n cael effaith anarferol o fawr ar ei hamgylchedd o ystyried ei biomas e.e. eliffant ar safana.