Summary of Chapter Concepts

Succession occurs in a community when species replace each other over time. The process of succession can be observed through either direct observations over time or indirect observations that use chronosequences or parts of organisms such as pollen that have been naturally preserved over time. Succession occurs on land, where we can distinguish between primary and secondary succession, and in the water. Succession often does not follow a simple linear path of species replacements, but there is a common pattern of rapidly increasing species richness over time that plateaus and can subsequently exhibit a small decline.

Succession can occur through different mechanisms. The mechanisms of succession can be categorized as facilitation, inhibition, and tolerance. More than one mechanism can operate in a community experiencing succession and the traits of species help determine the mechanisms that occur and where each species occurs along the successional stages.

Succession does not always produce a single climax community. As succession proceeds, the environment continues to change until conditions reach a point of relative stability and the dominant species appear to be persistent. However, the climax community can continue to experience slow changes over time. The climax community can also differ within a region along environmental gradients such as temperature and moisture. Some climax communities are transient because they experience regular disturbances that reset succession, such as vernal pools that dry each summer. Extreme conditions, including fires and intense grazing, can also alter climax communities to produce a different composition of dominant organisms.