Question

Use the following scenario to answer question.

Island chains are known to occur along the borders of the earth’s large land plates. For example, both the Hawaiian and Galapagos Islands were born from the intense volcanic activity generated along the Pacific Ocean’s “Ring of Fire”. Hence, the number and placement of the islands can tell us approximately how many of the underwater volcanoes made islands and in what direction the plates are moving. Once formed, an island, then undergoes colonization by living organisms. We often describe a successful colonization event as one where the species lands, breeds and its offspring remain on the island to repeat its life cycle. In the case of Krakatau, which is a volcanic island in Indonesia, we have many recordings of its recolonization by life forms after the 1883 eruption which wiped the island clean of all preceding life forms. One of the first groups of organisms to colonize was that of spiders and insects.

11.What type of selection pressure would enhance the survival of the spiders and insects once they landed on the new Krakatau Island? Why? (i.e. divergent, convergent)

12.What kind of selection pressure would prevent the successful colonization by insects and spiders? Why?

Answer 1

Ans 11 - An island like that of krakatau has different niches. Darwin demonstrated that an island as small as the galapagos island had many different species of finches. This is an example of adaptive radiation. Adaptive radiation is a type of divergent evolution in which a subset of a species moves to a new niche and evolves to function optimally in that new niche. Hence divergent evolution would drive the survival of spiders and insects on the new Karatau island.

Ans 12 - Convergent selection pressure would prevent the successful colonization. Convergent selection is a force that ensures that a species is very specialised to a certain niche. If all the spiders and insects were specialized to only one niche and thus there would be fierce competition. In such a case, Gause's exclusion principle comes into play. The principle states that hat two species competing for the same limiting resource cannot coexist at constant population values. When one species has even the slightest advantage over another, the one with the advantage will dominate in the long term. This leads either to the extinction of the weaker competitor. This indicates that diversification is necessary for the survival of members within a certain species and the survival of various species in niches.