The average number of individuals of a species per unit area of the habitat is the?

1. Analyze the question The question asks for the term describing the number of individuals of a species per unit area of a habitat. The key phrase is "per unit area", which points to a measure of how crowded a population is.

2. Explain the concept

• Population density: the number of individuals per unit area (or volume) of the habitat. Formula: Population density = Total number of individuals ÷ Total area occupied.
• Population frequency: how often a species occurs in sampled quadrats, usually shown as a percentage of the quadrats in which it appears. It is not a count per unit area.
• Population size: the total number of individuals of a species in a habitat, with no reference to area.
• Population distribution: the pattern of spread of individuals in the habitat (random, uniform, or clumped).

3. Step-by-step solution

• Step 1: Identify the key phrase, "per unit area".
• Step 2: Match it to the definition. Only population density is defined as a number per unit area.
• Step 3: Eliminate the others: • B measures how often the species is encountered, not a count per area. • C is the total count only. • D describes the spatial arrangement.

Example: If 200 grasshoppers are found in a 50 m² field, the population density is 200 ÷ 50 = 4 grasshoppers per m².

4. Answer The correct option is A. population density.

5. Exam tip Link the words to the meaning:

• Density = Dividing the number by the area (per unit area).
• Size = Simply the total count.
• Distribution = the pattern of spread.
• Frequency = how often it shows up in samples.

If a question says "per unit area" or "per unit volume," think density.