Which statement is not related to S-shaped population curve?

Options

A. Environmental resistance suddenly becomes effective.
B. Exponential phase is followed by decline phase.
C. Mass mortality and population crash occurs.
D. Both (1) and (3).

Answer

To determine which statement is not related to the S-shaped population curve, we need to analyze the characteristics of S-shaped (logistic) population growth and compare them with the provided options.

### Step-by-Step Solution:

1. **Understand S-shaped Population Curve**: The S-shaped curve, also known as logistic growth, represents how a population grows in an environment with limited resources. Initially, the population grows exponentially, but as resources become limited, the growth rate slows down and eventually stabilizes at the carrying capacity (K) of the environment.

2. **Identify Key Features of S-shaped Curve**:
- **Exponential Growth Phase**: The population grows rapidly when resources are abundant.
- **Deceleration Phase**: As the population approaches the carrying capacity, growth slows down due to increased competition for limited resources.
- **Stabilization Phase**: Eventually, the population stabilizes around the carrying capacity, where the birth and death rates balance.

3. **Evaluate Each Statement**:
- **Statement 1**: "Environmental resistance suddenly becomes effective."
- This statement is **not true** for the S-shaped curve because environmental resistance is always present due to limited resources, not something that suddenly occurs.

- **Statement 2**: "Exponential phase is followed by a decline phase."
- This statement is **true** for the S-shaped curve as the exponential growth is followed by a slowing down of growth.

- **Statement 3**: "Mass mortality and population crash occurs."
- This statement is **more related to the J-shaped curve**, where a sudden crash occurs after exceeding carrying capacity, not typically associated with the S-shaped curve.

- **Statement 4**: (Assuming a fourth statement is provided) Analyze it similarly to determine its relation to the S-shaped curve.

4. **Conclusion**: Based on the analysis, the statements that are not related to the S-shaped curve are:
- **Statement 1**: Environmental resistance suddenly becomes effective.
- **Statement 3**: Mass mortality and population crash occurs (more related to J-shaped).

Thus, the answer to the question is that **Statement 1** is not related to the S-shaped population curve.