Historically, island species have tended to become extinct faster than species living on a mainland. Which of the following reasons can not be used to explain this phenomenon?

Options

A. Island species have often evolved in the absence of predators and have no natural avoidance strategies
B. Humans have introduced diseases and competitors to islands, which negatively impacts island populations
C. Island populations are usually smaller than mainland populations
D. Island populations are usually less fit than mainland populations

Answer

To answer the question regarding why island species tend to become extinct faster than mainland species, we need to analyze each of the provided options and determine which one cannot be used to explain this phenomenon.

### Step-by-Step Solution:

1. **Understanding the Context**:
- Island species often face unique challenges compared to mainland species. These challenges can include limited resources, smaller population sizes, and different ecological dynamics.

2. **Analyzing Option 1**:
- **Statement**: "Island species have often evolved in the absence of predators and have no natural avoidance strategy."
- **Evaluation**: If there are no predators, island species might not face the same pressures that mainland species do. This statement suggests that the absence of predators would lead to an increase in population rather than extinction. Thus, this option cannot explain the faster extinction of island species.

3. **Analyzing Option 2**:
- **Statement**: "Humans have introduced disease and competition to the island, which negatively impacts the island population."
- **Evaluation**: The introduction of diseases and competition can indeed lead to population decline and extinction. This option can explain the extinction phenomenon, as it highlights human impact on island ecosystems.

4. **Analyzing Option 3**:
- **Statement**: "Island populations are usually smaller than mainland populations."
- **Evaluation**: Smaller populations are often more vulnerable to extinction due to factors like genetic drift and reduced reproductive rates. This option can also explain the extinction of island species.

5. **Analyzing Option 4**:
- **Statement**: "Island populations are usually less fit than mainland populations."
- **Evaluation**: If island populations are less fit, they may struggle to survive in their environment, leading to higher extinction rates. This option is valid in explaining the phenomenon.

6. **Conclusion**:
- The option that cannot be used to explain why island species become extinct faster than mainland species is **Option 1**. The absence of predators should not lead to extinction; rather, it should allow for population growth.

### Final Answer:
The reason that cannot be used to explain the faster extinction of island species compared to mainland species is: **"Island species have often evolved in the absence of predators and have no natural avoidance strategy."**