Problem 9 - Biology: The Dynamic Science

Question

The equilibrium theory of island biogeography predicts that the number of species found on an island: a. increases steadily until it equals the number in the mainland species pool. b. is greater on large islands than on small ones. c. is smaller on islands near the mainland than on distant islands. d. can never reach an equilibrium number. e. is greater for islands near the equator than for islands near the poles

Step-by-Step Solution

Answer

The correct answer is option b, which states that the number of species is greater on larger islands than on small ones.

Step 1: Understand the Theory

In the equilibrium theory of island biogeography, the number of species on an island reaches an equilibrium based on the balance between immigration and extinction rates. Island size and distance from mainland are two key factors.

Step 2: Evaluate the Options

Evaluate each option with reference to the theory. Remember that larger islands and islands closer to the mainland theoretically have more species due to higher immigration and lower extinction rates.

Step 3: Choose the Correct Option

Option b states that larger islands have more species - an idea that aligns with the equilibrium theory, as larger islands can support more species. This makes it the correct choice.

Key Concepts

Equilibrium Theory

The equilibrium theory of island biogeography is a fundamental concept in ecology, focusing on how species come to populate and live on islands. At the heart of this theory is the idea of balance. On islands, the number of species is not just random; instead, it finds a natural balance point, where the rate of new species arriving (immigration) matches the rate of species disappearing (extinction).
Contrary to a common misunderstanding, this balance does not mean the number of species stays the same forever. Instead, it indicates a dynamic equilibrium, where, although specific species might come and go, the overall number stays relatively stable.
The theory suggests that larger islands have a higher equilibrium number of species compared to smaller islands. This is due to larger habitats being able to sustain more individuals and different species. Similarly, islands closer to the mainland have higher equilibrium levels because they receive more immigrants, helping maintain a stable species count.

Species Richness

Species richness refers to the number of different species represented in a given area, like an island, region, or ecosystem. In the context of island biogeography, it refers to the diversity of species that an island can support.
Larger islands tend to have greater species richness. This is largely because they provide a more extensive variety of habitats, resources, and niches that different species can exploit.
Similarly, proximity to the mainland enhances species richness because more species can easily reach the island to establish a new population. This concept is essential to understanding why some islands have a far richer variety of life than others, despite similar climates.

• Greater variety of habitats on larger islands boosts species richness.
• Close islands enjoy more frequent species immigration, enhancing diversity.
• Species richness is not static; it is influenced by ongoing ecological dynamics.

Immigration and Extinction Rates

Immigration and extinction are key processes underlying the equilibrium theory and shaping species richness on islands. **Immigration** refers to the arrival of new species on an island, often from a nearby mainland.
**Extinction**, in this context, denotes the loss of species from the island ecosystem. Both rates are dynamic and can fluctuate based on several factors.
Larger islands generally experience higher immigration rates because they are more visible or accessible, making them easier targets for colonizing species. With more space and resources, they also usually see lower extinction rates.
Meanwhile, islands closer to the mainland benefit from higher immigration rates simply due to proximity. This allows species to arrive more frequently, thus enhancing species richness and maintaining a stable balance against extinction.

• Larger islands: higher immigration, lower extinction rates.
• Close to mainland: higher immigration rates.
• The balance of these rates determines the number of species an island can sustain.