问GWD里的一句话，不太理解

yuanzi15

 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.  尤其是红字部分，什么语法啊，不太理解，请高手指点

yuanzi15

解释得非常到位，感谢ing!