文章中： Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear. 哪位说说最后这几个词的语法是怎样的好么？不懂：（。。。谢谢：）

题目中也是一样的结构，猜得出意思，不知道语法关系：（

1. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover

an environmentally degraded stream could be recolonized by new salmon populations should the stream recover

我其实也想知道为什么的，hehe，

populations ( if )the stream should recover

虚拟语气:如果那里的鱼消失

A: 如果那里的河流恢复

有时if引导的状语从句可以省略 if，而把从句中的动词 were, had 或 should 移到主语前面