Scientists typically start thinking of a new name for a species when significant genetic and morphological differences accumulate within a population, leading to reproductive isolation from other populations of the same species. This reproductive isolation means that individuals from different populations can no longer successfully interbreed to produce fertile offspring. At this point, scientists may consider the population to be distinct enough to warrant classification as a new species and assign it a unique scientific name.
1. In Model 1, the graphs for directional selection, disruptive selection, and stabilizing selection compare the following variables:
1. Directional Selection:
- In directional selection, one extreme phenotype is favored over the other extreme or intermediate phenotypes.
- The variable being compared is the distribution of phenotypes in a population over time.
- It shows a shift in the population's phenotype distribution towards one extreme of the trait.
2. Disruptive Selection:
- In disruptive selection, extreme phenotypes are favored over intermediate phenotypes.
- The variable being compared is the distribution of phenotypes in a population over time.
- It shows an increase in the frequency of individuals with extreme phenotypes and a decrease in the frequency of individuals with intermediate phenotypes.
3. Stabilizing Selection:
- In stabilizing selection, intermediate phenotypes are favored over extreme phenotypes.
- The variable being compared is the distribution of phenotypes in a population over time.
- It shows a decrease in the frequency of individuals with extreme phenotypes and an increase in the frequency of individuals with intermediate phenotypes.
Overall, the comparison involves the distribution of phenotypes within a population and how selection pressures influence the frequency of different phenotypic traits over time.
2. In Model 1 - Three types of selection, the three types of selection illustrated in the graphs are:
1. Directional Selection:
- This type of selection occurs when one extreme phenotype is favored over the other extreme or intermediate phenotypes.
- It is represented by a shift in the population's phenotype distribution towards one extreme of the trait.
2. Disruptive Selection:
- Disruptive selection occurs when extreme phenotypes are favored over intermediate phenotypes.
- It is represented by an increase in the frequency of individuals with extreme phenotypes and a decrease in the frequency of individuals with intermediate phenotypes.
3. Stabilizing Selection:
- Stabilizing selection occurs when intermediate phenotypes are favored over extreme phenotypes.
- It is represented by a decrease in the frequency of individuals with extreme phenotypes and an increase in the frequency of individuals with intermediate phenotypes.
These types of selection illustrate different mechanisms by which natural selection can act on populations, leading to changes in the distribution of phenotypic traits over time.
