Question

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

The lizard population first got divided into two due to a barrier, and then into three by a major flood event. The three separated populations will slowly accumulate different changes due to differences in the environments they live. Over time, the differences would be such, that the three populations can no longer mate even when they ocassionally meet. At this point, the three would have formed three separate species. Such a speciation event that takes place as a result of geopgraphical barrier is called allopatric speciation.