Keystone species?

*[ʃʌʃ]\nn. 关闭\nvt. 关上, 闭起, 幽禁, 合拢, 轧住\nvi. 关上, 停止营业\n【经】 关闭, 停止营业\n相关词组:\n shut one's eyes to the facts\n shut one's ears to all advice\n be shut of sb\n shut down\n shut down on\n shut in\n shut sth off\n shut out\n shut sb out of the room\n shut to\n shut up\n shut the door against sb\n shut the door upon sb\n shut the door in sb's face