The ecological succession of species within specific habitat happens because each community changes that community in ways that benefit other species. Eventually succession results in a diverse and stable community of organisms.

Primary Succession

Primary succession begins in an area of little or no soil or where catastrophic events remove all the organisms. The first organisms to arrive take hold and modify the local environment to suit the succeeding community but not themselves, and are replaced by other species better suited to the new environment.

Opportunistic Species

Primary succession begins with opportunistic species able to live in the environment. As they die, they contribute organic matter to the environment, providing a place for other organisms to live which continue on in the process of secondary succession.

Secondary Succession

As the ecological community develops and grows within a specific area, it modifies the habitat in ways that benefit other species. This environmental change results in a predictable succession of organisms that establish themselves, contributing to an ever widening of species diversity.

Species Diversity

As the number of species with an ecosystem grows, fewer changes take place within the ecological community. Each species supports the others in various ways. As a result, the progression of succession slows.

Climax

The end result of secondary succession is a climax ecology. The species within the community are diverse enough to support each other without one species overtaking another. This stage of succession continues until some catastrophic event like a forest fire pushes the community into an earlier stage of succession.

Regression

When a catastrophic event occurs, the ecological community returns to an earlier succession stage, possibly the primary stage of succession. Organisms better able to cope with the environment are established once again and secondary succession continues.

Source:

Indiana University of Pennsylvania: Ecological Succession

More Information:

Biology Online: Ecosystem Succession