Question

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B. Consider the following scenario. A large population of lizards occupies an extensive range that is relatively uniform ecologically (i.e., in terms of climate and co-occurring species). At a certain point in time, the ancestral population becomes divided down the middle into two similar-sized portions by a barrier that completely prevents the movement of lizards between the descendent populations. Around the same time, a major flood occurs, and a small number of individuals are swept away from the mainland on floating debris and arrive alive on a small offshore island that has no lizards of this species. The habitat on the island is similar to their homeland, but not identical (the climate is slightly different, many mainland species of plants and animals are absent, and a few island species of plants and animals are different from any present on the mainland. Thus, there are now three separate populations. Compare and contrast the expected evolutionary consequences for these populations in the future.

Answer 1

When there is division by a barrier and the species are unable to move from one side to the other, slowly over time there is reproductive isolation due to mutations and thus it leads to speciation. This kind of speciation is called allopatric vicariant speciation. The geographical barrier can cause the two populations to separate on the basis of environmental pressure, leading to genetic drift. There can be phenotypic changes associated with genotypic ones ultimately leading to the formation of a separate species.

The population of lizards that are washed off to the island, also start utilizing resources available on the island, and also adapt to changes that are there on the island. A small population moves to the island and thus there is small genetic variation in them. This leads to the fixation of an allele in the population and thus divergence from the original population finally leading to reproductive isolation and forming a new species. this type of speciation is called peripatric speciation.