with an example of the peppered moths when they changed color from light to dark due to pollution, what selection pressure is this? disruptive, stabilizing or directional?
http://www.sparknotes.com/biology/evolution/naturalselection/section1.rhtml
OMG I did this one before!
To determine the selection pressure acting on the peppered moths when they changed color from light to dark due to pollution, we need to consider the three types of selection pressures - disruptive, stabilizing, and directional - and their characteristics.
Disruptive selection occurs when extreme phenotypes have a higher fitness compared to the intermediate ones. This results in the population diverging into two or more distinct phenotypes.
Stabilizing selection, on the other hand, favors the intermediate phenotype over extreme phenotypes. This leads to a reduction in genetic variation within the population.
Finally, directional selection acts on one extreme phenotype, causing a shift in the population towards that extreme. This results in a change in the average phenotype over time.
In the case of the peppered moths, the selection pressure is directional. Before industrial pollution, the light-colored moths were favored as they efficiently blended with the lichen-covered trees. However, with the advent of pollution and widespread darkening of tree trunks, the dark-colored moths gained a survival advantage as they were better camouflaged against the darkened tree bark. Over time, the population shifted towards a higher frequency of dark-colored moths, leading to a change in the average phenotype.
So, in summary, the selection pressure acting on the peppered moths when they changed color from light to dark due to pollution is directional.