2. When the Isthmus of Panama between North and South America was uncovered, som

Question

2. When the Isthmus of Panama between North and South America was uncovered, some North American mammal lineages crossed to South America and underwent rapid speciation into many new species. (a and b worth 1 point each, c worth 2 points)

a) For terrestrial species, did the occurrence of the land bridge represent a vicariance or dispersal event?

b) Did the recent construction of the Panama Canal represent a vicariance or dispersal event for terrestrial organisms? For marine organisms? Explain your answers.

c) Morphologically similar species of snapping shrimp that are each others' closest relatives live on either side of the Isthmus of Panama. Explain why this observation supports the hypothesis that speciation occurred via vicariance.

Explanation / Answer

a. When the Isthmus of Panama was uncovered between N.America and S.America, the terretrial species of N.American lineages crossed to S.America or reverse. This represents a dispersal event since they move to colonize a new habitat and undergo speciation.

b. The recent construction of Panama canal has lead to geogrphical separation of terrestrial organisms of either side by a barrier. Hence, this is a vicariance event. In case of marine animals, it is termed as a dispersal event because the opening of Panama canal allows the movement of species from Atlantic ocean to Pacific ocean and vice versa.

c. The species of snapping shrimps were geographically separated by Isthmus of Panama and subsequently divided into two groups due to interruption of gene flow. This is a result of vicariance. In different niches, they underwent different evolutionary process and finally became incapable of interbreeding. This is how new species originated, hence speciation occurred via vicariance.

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