Problem 4 - Campbell Biology

Question

Knowledge/Comprehension According to the island equilibrium model, species richness would be greatest on an island that is (A) large and remote. (B) small and remote. (C) large and close to a mainland. (D) small and close to a mainland.

Step-by-Step Solution

Answer

C) large and close to a mainland.

Step 1: Understand the Variable

Island equilibrium model explains species richness based on island size and distance from the mainland.

Step 2: Analyze Island Size

Species richness increases with a larger island size because there is more available habitat and resources.

Step 3: Evaluate Distance

Islands closer to the mainland have higher species richness due to easier immigration and gene flow.

Step 4: Combine Factors

Considering both factors, an island that is both large and close to a mainland would have the greatest species richness.

Key Concepts

Species Richness

Species richness refers to the number of different species present in a particular region or ecosystem. It is an important measure of biodiversity and can vary greatly depending on multiple factors, such as habitat availability, resources, and ecological interactions. In the context of islands, species richness is a key focus of the island equilibrium model.
The island equilibrium model, proposed by Robert MacArthur and E.O. Wilson, suggests that the number of species on an island is determined by a balance between immigration (new species arriving) and extinction (species disappearing).
When an island has high species richness, this balance implies lower extinction rates due to a larger variety of species occupying various niches and better resilience to disturbances.
For students trying to understand why certain islands have more species than others, considering aspects like the size of the island and its distance from the mainland can help clarify why this is the case.

• Larger islands can support more species due to a greater variety of habitats and resources.
• Islands closer to the mainland can easily receive new species due to shorter travel distances.

Island Size

The size of an island is one of the most crucial factors influencing species richness. Larger islands tend to have more species than smaller islands for several reasons:
First, larger islands offer more space and diverse habitats. This means that more species can find suitable conditions for survival and reproduction. Additionally, larger habitats reduce the chances of extinction due to higher availability of resources even during tough environmental conditions.
Second, on larger islands, there is a lower likelihood of any single catastrophic event wiping out entire populations, providing a form of ecological insurance.

• More space leads to a higher variety of ecosystems, such as forests, rivers, and meadows, each supporting different species.
• Larger land areas also mean that populations can spread out, reducing competition and leading to higher overall survival rates.

Consequently, this availability of space and variety plays a major role in maintaining and increasing species richness on larger islands.

Distance from Mainland

Distance from the mainland is another critical determinant of species richness on islands. Islands closer to the mainland generally have higher species richness due to easier access for species migrating from the mainland.
As distance from the mainland increases, it becomes harder for species to travel to the island, resulting in lower immigration rates. This reduced flow of new species means that isolated islands are less likely to gain new species, and the species that do reach these islands have to adapt to more isolated environments.
Additional factors influenced by the distance from the mainland include:

• Gene flow: Closer islands receive more genetic diversity through continuous gene flow from mainland populations, helping species adapt and thrive.
• Ecosystem support: Frequent immigration from the mainland helps replenish populations and supports the ecosystem's resilience.

Thus, proximity to the mainland plays a significant role in ensuring consistent species influx and diversity on the island.
Combining these factors, the island closest to the mainland is more likely to maintain and increase its species richness.