一个很短的难句跪求解释！

就是这种类型的话不会理解 为什么句子中有两个情态动词？

the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear。

the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear

这个句子有倒装，还原以后应该是这样：

a mechanism by which a location （the fish there should disappear） can be repopulated

谢谢 LS 的 但这也太奇怪了……