The moai, he thinks, accelerated the self-destruction. Diamond interprets them as power displays by rival chieftains who, trapped on a remote little island, lacked other ways of asserting their dominance
这里who，trapped是定语从句的什么用法，定语从句不是要么who is trapped。或者省略引导词和be，直接用trapped。这里who+逗号+trapped是什么用法？
