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
大的结构没有问题，Low levels of straying are crucial, since the process provides A and B 但是红色的部分不太明白，a mechanism by which a location can be repopulated should the fish there disappear 请问怎么来划分这句从句？