Question

please thoroughly explain, thank you.

B. Consider the following scenario. A large population of lizards occupies an extensive range that is rela-tively 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 evolu-tionary consequences for these populations in the future.

Answer 1

Ans - In future speciation will took place. There will be 2 new species formed from the ancestral one. one species will be formed due to division of geographical area by barrier(Allopatric speciation). and one species will be formed due to entering a new place (Parapatric Speciation)

Speciation refers to the origin of new species from pre existing one. It forms the basis of entire course of evolution. The process of splitting a genetically homogenous population into two or more population that undergoes genetic differentiation and eventually reproductive isolation is called speciation.

Allopatric speciation (allo-other, patric- place) is genetic divergence permitted by geographical isolation. This process is dependent on random mutation, which accumulates steadily after a population has been subdivided in space. This subdivision can take place because of geographic barrier such as mountain ranges and water bodies. Because of which two sub-populations are then reproductively isolated, each of the populations accumulates in different mutations and the two populations diverge.

This divergence is a strongest where the population size of one or both others are populations is a small because sampling error is high in smaller population. These differences will eventually lead to reproductive incompatibilities that will be keeping the population distinct.

Parapatric Speciation- (Para- beside, patric- place) is a form of speciation in which the evolution of reproductive isolating mechanisms occurs when a population enters a new niche or habitat within the range of the parent species. Generally, this occurs when there has been a drastic change in the environment within the original species habitat. chromosomal aberrations acn occur in them which lead to partial reproductive isolation in the individuals of a population in some areas of its distribution. The lower fertility with further addition of structural changes in the chromosomes finally establishes reproductive isolation forming new species.

In parapatric speciation, there is no specific extrinsic barrier to gene flow. The population is continuous but nonetheless the population does not mate randomly. Individuals are more likely to mate with their geographic neighbours than with individual in different part of population's range. In this mode,divergence may happen because of reduced in flow within the population and varying selection pressures across the population's range.