North and South American species migrating across the Isthmus now came into competition with each other.
北美和南美的物种迁徙穿过地峡，现在开始互相竞争。
2
Second, it appears that closely related populations of fishes on both sides of the isthmus are starting to genetically diverge from each other.
其次，地峡两侧紧密相关的鱼类种群似乎开始在基因上彼此分化。
3
While previously the gap between the continents had allowed a free flow of water, now the isthmus presented a barrier that divided the Atlantic Ocean from the Pacific Ocean.