Question

Two ecologists, Robert H. MacArthur and Edward Wilson, studied how organisms immigrate to islands and how their numbers change after colonization. They developed the island biogeography model to explain the composition and diversity of island species. The graph below shows the number of species versus the size of the Caribbean island:

Use the Species by Area graph and your knowledge of how organisms can immigrate to answer the following:
Identify the likely scientific question being investigated in the study.
Describe the relationship between species number and island size observed in the data.
Explain how the experiment results would change if the islands had frequent ships that docked on them from distant bodies of water.

Scientists have found that most species on the same continent are more closely related to each other than to organisms on other continents. They hypothesize that this phenomenon is due to the evolution that occurred after the continents split apart, or in the case of island biogeography, after islands formed off the coast of mainland regions.
Explain the role of adaptive evolution in island biodiversity.
Describe one process that leads to speciation of islands.
Explain how the biodiversity of an island affects its ecological tolerance to change.
Explain how specialist species are affected when generalist species migrate to an island.

Island ecosystems experience ecological succession in different stages of their development.
Describe the process of primary succession on an island.
Describe the process of secondary succession on an island.
Identify two scenarios that lead to secondary succession on an island. Explain how these scenarios can affect island biodiversity.

Answer 1

The likely scientific question being investigated in the study is how island size affects the number of species present on an island. The data shows that as island size increases, the number of species present on the island also increases.

If the islands had frequent ships that docked on them from distant bodies of water, it would likely increase the number of species on the islands. This is because more organisms would be able to immigrate to the islands, increasing the overall diversity of species.

Adaptive evolution plays a key role in island biodiversity by allowing organisms to adapt to the unique conditions of the island. This can lead to the development of new species that are better suited to the island environment.

One process that leads to speciation of islands is genetic isolation. This can occur when a population of organisms becomes physically separated from the mainland population and is unable to interbreed with it. Over time, the isolated population will evolve differently from the mainland population, eventually leading to the development of a new species.

The biodiversity of an island affects its ecological tolerance to change by providing a greater range of organisms that can respond to changes in the environment. This can increase the chances of survival for the island ecosystem as a whole.

When generalist species migrate to an island, they may outcompete the specialist species that are already present. This can lead to a decrease in the number of specialist species on the island, as they are unable to survive in the presence of the more adaptable generalist species.

Primary succession is the process of an ecosystem developing on a previously uninhabited area. This can occur on an island that has recently formed from volcanic activity, for example.

Secondary succession is the process of an ecosystem developing after a disturbance has occurred on a previously inhabited area. This can occur on an island after a natural disaster or human activity has caused damage to the ecosystem.

Two scenarios that lead to secondary succession on an island are natural disasters such as hurricanes and human activities such as deforestation. These scenarios can affect island biodiversity by altering the conditions of the island and causing a loss of species. The loss of biodiversity can make the ecosystem more vulnerable to future disturbances and changes.