地峡是连接两块较大陆地或较大陆地与半岛间的狭窄地带。前者如连接亚、非两洲的苏伊士地峡，连接南、北美洲的中美地峡；后者如连接中南半岛与马来半岛的克拉地峡（Kraisthmus），连接乌克兰与克里米亚半岛间的彼列科普地峡（Perekopskiyisthmus）等。地峡便于开凿运河以沟通两侧海洋，如已建成的苏伊士运河与巴拿马运河等。
地峡的形成对全球洋流格局产生了重要的影响。
The formation of the isthmus had important consequences for global patterns of ocean water flow.
北美和南美的物种迁徙穿过地峡，现在开始互相竞争。
North and South American species migrating across the Isthmus now came into competition with 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。
Second, it appears that closely related populations of fishes on both sides of the isthmus are starting to genetically diverge from each other.
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