18: Ecological Succession

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Learning Objectives

Introduce succession by exploring the history of its theory
Describe role of disturbance and expected outcomes regarding diversity
Summarize important models of successional change
Go beyond plants by investigating the roles of consumers in succession

18.1: Introduction
Ecological succession is the process of change in the species structure of an ecological community over time. It is a process by which an ecological community undergoes more or less orderly and predictable changes following a disturbance or the initial colonization of a new habitat. Succession may be initiated either by formation of new, unoccupied habitat, such as from a lava flow or a severe landslide, or by some form of disturbance.
18.2: What are the Effects of Disturbance?
In ecology, a disturbance is a temporary change in environmental conditions that causes a pronounced change in an ecosystem.
18.3: Patterns of Diversity Following Disturbance
Disturbance typically increases diversity at the landscape scale, but intense disturbances can initially decrease diversity at the site scale. This scale-dependent process can be described with different diversity metrics, some of which we will explore in this chapter; others will be introduced later.
18.4: What causes successional change?
The trajectory of successional change can be influenced by site conditions, by the type of events initiating succession, by the interactions of the species present, and by more stochastic factors such as availability of propagules or weather conditions at the time of disturbance.
18.5: The Role of Consumers and Alternative Stable States
Communities of consumers also undergo succession as plant communities change through time. Animals can also redirect successional trajectories for whole communities, changing the final community structure dramatically.

Summary

Succession, or the process of change in the species composition of a community over time, was one of the first theories developed in ecology. Succession is brought about by environmental disturbances, and generally speaking, disturbance increases biodiversity. However, the level of disturbance significantly influences species diversity and may be maximized at intermediate levels. The patterns of successional change in biodiversity are scale dependent and must be quantified appropriately using alpha, beta, and gamma diversities. There are three common models used to explain the dynamics of community development through succession. In these models pioneer species facilitate, inhibit, or can be tolerated by later successional organisms. Succession is commonly framed within plant communities. However, animal communities affect succession through phenomena like the redirection of successional trajectories and the development of alternative stable states.