Which of the following statements about determining population size is correct?

• A. Quadrat sampling cannot be used for estimating population size.
• B. Direct observation is the simplest method, but it is not always the most effective for large or mobile populations.
• C. Mark-recapture is less accurate than direct observation in all cases.
• D. Direct observation is always the most accurate and practical method for all populations.

Answer: (B)

Verified step by step guidance

1. Understand the context of the question: The problem is asking about methods used to determine population size in ecology. These methods include quadrat sampling, direct observation, and mark-recapture. Each method has its strengths and limitations depending on the type of population being studied.
2. Step 1: Evaluate the statement about quadrat sampling. Quadrat sampling is a method used to estimate population size, especially for stationary or slow-moving organisms like plants or small animals. The statement that 'quadrat sampling cannot be used for estimating population size' is incorrect because it is a widely used method in ecology.
3. Step 2: Analyze the statement about direct observation. Direct observation involves counting individuals in a population directly. While it is the simplest method, it is not always the most effective for large or mobile populations because it can be time-consuming, impractical, or inaccurate in such cases. This aligns with the correct answer provided in the problem.
4. Step 3: Examine the statement about mark-recapture. Mark-recapture is a method used for mobile populations, where individuals are captured, marked, released, and then recaptured to estimate population size. The statement that 'mark-recapture is less accurate than direct observation in all cases' is incorrect because mark-recapture can be more effective for mobile populations where direct observation is impractical.
5. Step 4: Assess the statement about direct observation being always the most accurate and practical method. This is incorrect because direct observation is not always practical or accurate for all populations, especially for large, mobile, or cryptic species. Other methods like mark-recapture or quadrat sampling may be more suitable in such cases.