Ecological succession refers to

Step 1: Analyze the question The question asks for the definition of ecological succession. Break the term down: "ecological" relates to organisms and their environment, and "succession" means one thing following another in order.

Step 2: Explain the concept Ecological succession is the gradual, orderly, and fairly predictable replacement of one community of organisms by another over time in the same area, until a stable community called the climax community is reached.

There are two types:

• Primary succession: starts on bare ground with no soil, such as bare rock or a new lava flow. Pioneer species like lichens and mosses come first.
• Secondary succession: occurs where a community was destroyed but soil remains, such as an abandoned farmland in Nigeria that returns to bush, then shrubs, then forest.

A typical sequence: pioneer species (lichens, mosses) → grasses and herbs → shrubs → trees → climax community.

Step 3: Evaluate each option

• A. Movement of organisms from one habitat to another: this describes migration or dispersal, not succession.
• B. Competition among species for limited resources: this is interspecific competition. It can happen during succession but is not its definition.
• C. Natural selection in a population: this is an evolution concept, not an ecological one.
• D. Gradual and predictable change in a community over time: this matches the definition exactly.

Step 4: Answer The correct option is D.

Exam tip: Link the word "succession" with "sequence". Whenever you see a question on succession, look for words like gradual, orderly, replacement, and climax community. Migration = movement, competition = struggle for resources, natural selection = evolution, so you can eliminate those quickly.