The above figure shows the trajectory of arthropod species richness over time fo

Question

The above figure shows the trajectory of arthropod species richness over time for four mangrove islands after fumigation to remove all arthropods. The single values on the left show the total no. of arthropod species on each island before fumigation. The islands are labelled, in order of distance from the mainland, as E2, E3, ST2 and E1. The islands were of roughly similar size.

Question 1. What prediction(s) of the theory of island biogeography do these data support?

Question 2. What do you predict the species richness of each island will be 1000 days after fumigation? Why?

Explanation / Answer

Ans.1. The equilibrium theory of island biogeography proposed that the number of any species on an island is determined by the balance between the rate of immigration from the mainland to the island and the rate of extinction of species on the island. In other words, the balance between the rate at which new species colonize and the rate at which populations of established species become extinct.

The rate of immigration and extinction is affected by the two physical feature of the island that is its size and its distance from the mainland.

In order of distance, the island that is more isolated from the mainland has a lower immigration rate than the close island. Therefore, the farthest island has the higher number of particular arthropod species as the rate of immigration of new species decreases due to the less competitive exclusion which results in the lower rate of extinction. While the nearest island may also has the higher number of species richness but due to the higher interspecific and intraspecific competition, the rate of extinction is also high.  Therefore, the number of arthropods species follows the order as E2, E3, ST2 and E1 according to the distance from the main island.

Ans.2. The species richness on an island depends on the rate of immigration. The rate of immigration depends upon the distance from the mainland. The increased rate of immigration increases the species richness on the nearest island to the mainland than the far island. But due to the fumigation which is a method of pest control, the species richness on an island is also affected.

As E2 island is closest to the mainland, therefore, the rate of immigration and species richness is very high as compared to the other island. After 1000 days of the application of fumigation, probably few species which become resistant may survive. Therefore, E2 island species richness is least affected by the fumigation.

While the species of arthropods on island E3 and ST2 is moderately affected by the fumigation. But the species of arthropods on island E1 is severely affected by the application of fumigations. As the lower number of species is present on this island probably unable to resist the effect of fumigation. And this might result in the extinction of species on E1 island.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.