Question

Write two stories ,where you describe and illustrate two of the patterns of selection (directional, disruptive or stabilizing). Use your focal organism in these stories. my focal organism is house sparrow passer domesticus

The story has to correctly represent the pattern of selection, it doesn’t have to be perfectly biologically accurate. You MUST use two DIFFERENT selection patterns. For full points, each story must include the following: - a range or gradient of phenotypes - an environment or context where these organisms are found - the differential success of each phenotype in the described environment or context - a drawing that represents how the original population (see figure to the right) has changed - a label to indicate which pattern you are describing

Answer 1

Directional selection occurs when conditions favor individuals exhibiting one extreme of a phenotypic range, thereby shifting a population s frequency curve for the phenotypic character in one direction or the other. Directional selection is common when a population s environment changes or when members of a population migrate to a new (and different) habitat. For instance, an increase in the size of seeds available as food led to an increase in beak depth in a population of sparrows.

Disruptive selection occurs when conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes. One example is a population of black-bellied seedcracker finches in
Cameroon whose members display two distinctly different beak sizes. Small-billed birds feed mainly on soft seeds, whereas large-billed birds specialize in cracking hard seeds. It appears that birds with intermediate-sized bills are relatively efficient at cracking both types of seeds and thus have lower relative fitness.