Problem 4 - Campbell Biology

Question

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 Theory

The island equilibrium model, also known as the Theory of Island Biogeography, suggests that the number of species found on an island is determined by the balance between immigration of new species and extinction of existing species.

Step 2 - Factors Affecting Immigration

Large islands close to the mainland will have higher rates of immigration because they are easier to find for species coming from the mainland.

Step 3 - Factors Affecting Extinction

Large islands can support larger populations of each species, reducing the probability of extinction. Small islands have fewer resources, which can lead to higher extinction rates.

Step 4 - Combine the Factors

Considering both immigration and extinction rates, the island with the greatest species richness will be large (reduces extinction) and close to the mainland (increases immigration).

Step 5 - Choose the Correct Answer

Analyzing the given options, the correct selection based on the above steps is (C) large and close to a mainland.

Key Concepts

Species Richness

Species richness refers to the number of different species present in an ecosystem. It is a basic measure of biodiversity and plays a crucial role in understanding ecological balance.
On islands, species richness can vary greatly depending on several factors. Large islands tend to have more species because they offer more habitats and resources. This reduces competition and allows for a greater variety of species to coexist.
In contrast, small islands often support fewer species due to limited resources and habitats. For example, a small island may only have one type of food source, which can't support a wide variety of species.

Immigration and Extinction

The rates of immigration and extinction are pivotal in determining species richness according to the island equilibrium model.
**Immigration:** Larger islands close to the mainland experience higher immigration rates. This is because they are easier for new species to find and colonize. Each new species that arrives has the potential to increase species richness if it can survive and reproduce.
**Extinction:** Larger islands also tend to have lower extinction rates. They can support bigger populations of each species, which makes it less likely that any one species will die out due to random events. Small islands, however, are at higher risk of extinction because of limited resources and smaller populations.

Theory of Island Biogeography

The Theory of Island Biogeography, also known as the island equilibrium model, was developed by Robert MacArthur and Edward O. Wilson in the 1960s. This theory explains how species richness is determined by the interaction between immigration and extinction rates.
Here are some key points:

• **Immigration Rate:** This decreases as more species colonize the island because there are fewer species remaining on the mainland to immigrate to the island.
• **Extinction Rate:** This increases with the number of species present on the island due to competition for limited resources.
• **Equilibrium:** An equilibrium is reached where the rate of new species arriving equals the rate of species going extinct, thus maintaining a balance in species richness.

According to this theory, the ideal conditions for the greatest species richness are found on large islands close to the mainland, as these have high immigration rates and low extinction rates.