If it were not for this faculty, they would devour all the food available in short time and would probably starve themselves out of existence.

　　(虚拟语气)

　　【译句】如果不是具有这种能力，它们就会在短时间内吞掉所有能得到的食物，而且很可能会因饿死而灭绝。

　　分句1. If it were not for this faculty

　　分句2. they would devour all the food available in short time

　　分句3. would probably starve themselves out of existence

　　分句1 是虚拟语气的条件从句

　　分句2、3是并列关系，并且是主句。