What is the definition of population ecology?

Step 1: Analyze the question You are asked to define population ecology. Break the term into two parts:

• Population = a group of individuals of the same species living in the same area.
• Ecology = the study of organisms in relation to their environment.

So population ecology focuses on a single species' group, not on different species or the whole ecosystem.

Step 2: Explain the concept Population ecology studies how and why the number of individuals of one species changes over time and space. Key topics include:

• Population size and density
• Distribution (how individuals are spread out)
• Abundance
• Birth rate, death rate, immigration and emigration
• Growth patterns and limiting factors

Step 3: Evaluate each option

• A. Interactions between organisms and their physical environment: This is the general definition of ecology (or the study of the abiotic–biotic relationship), not specifically population ecology. ❌
• B. Evolutionary processes and their effects on populations: This describes population genetics or evolutionary biology. ❌
• C. Interactions between different populations in an ecosystem: This is community ecology (predation, competition, symbiosis between species). ❌
• D. The distribution and abundance of individuals within a species: This matches population ecology, which looks at where members of one species live (distribution) and how many there are (abundance). ✅

Step 4: Answer

Tip: Match the level of organization to the branch of ecology:

• One species → Population ecology
• Several species together → Community ecology
• Living and non-living things together → Ecosystem ecology

A quick memory trick: "Population = one species, how many and where."