The mode of natural selection in which one extreme phenotype is fittest and the environment selects against the others is:
disruptive selection.
uniformitarianism.
stabilizing selection.
artificial selection.
directional selection

Stabilizing selection

Explanation:

Natural selection is a process by which heritable traits conferring survival and reproductive advantage to individuals, or related individuals, tend to be passed on to succeeding generations and become more frequent in a population, whereas other less favourable traits tends to become eliminated.

Disruptive selection, stabilizing selection, artificial selection and directional selection are all types of natural selection. However, unlike others, stabilizing selection tends to lead the population of organisms towards the average trait instead of one or both extremes

from my research i have to the conclusion that decomposers, such as fungi, bacteria and invertebrates, play a critical role in nutrient cycling and without them the earth's ecosystem may not support life as we know it. elements such as carbon, nitrogen and phosphorus exist in limited amounts on earth, although huge amounts of carbon are being released into the atmosphere from underground sources now by humans. it is still extremely important that other nutrients be retained by the process of re-use. decomposers are organisms that are able to chemically break down dead material and make these elements available for use by other organisms. without this breakdown of dead material, dead bodies would pile up. so decomposers also play a role in clean up also. without them, life might not continue as we know it and dead material would overwhelm the earth.    

c. heat from the poles back down towards the equator.