Succession and Community Assembly

After a disturbance or on newly exposed ground, communities change in a more or less ordered sequence as species colonise, modify the habitat, and replace one another over time.

Definition

Succession and community assembly are the processes by which the species composition of a community changes over time following disturbance or substrate formation, and by which species colonise and sort into co-occurring assemblages.

Scope

This topic covers the temporal development of communities: primary succession on bare substrates and secondary succession after disturbance, the mechanisms of facilitation, tolerance, and inhibition that drive species replacement, and the concept and critique of the climax community. It includes assembly rules, the role of colonisation and dispersal in determining membership, and how disturbance regimes maintain diversity.

Core questions

• How does community composition change after disturbance or on new substrates?
• What mechanisms cause one set of species to replace another during succession?
• Is there a predictable endpoint, or climax, to succession?
• How do colonisation, disturbance, and assembly rules determine which species coexist?

Key theories

Facilitation, tolerance, and inhibition

Species replacement during succession can occur because early colonists make conditions suitable for later species (facilitation), because later species tolerate conditions regardless of earlier ones (tolerance), or because established species resist replacement until disturbed (inhibition).

Climax and the superorganism concept

Clements proposed that succession proceeds deterministically toward a stable climax community determined by climate, a view later qualified by recognition that disturbance, history, and chance produce multiple and shifting endpoints.

Mechanisms

Succession begins when colonists reach a site by dispersal; their establishment alters light, soil, and resource conditions in ways that may help, be neutral to, or hinder later arrivals. Through facilitation, tolerance, or inhibition, the relative competitive success of species shifts over time, producing turnover in composition. Recurrent disturbance resets portions of the community, and the interplay of disturbance frequency and intensity with colonisation can maintain a shifting mosaic rather than a single fixed climax.

Clinical relevance

Knowledge of succession guides ecological restoration, reforestation, rehabilitation of mined or burned land, and the management of disturbance regimes to sustain desired communities. This is educational context, not management prescription.

History

Cowles described dune succession around 1899 and Clements developed the deterministic climax model in 1916, which Gleason challenged with an individualistic view. Connell and Slatyer proposed the three mechanistic pathways of succession in 1977, and later work emphasised disturbance, priority effects, and alternative stable states.

Debates

Is succession deterministic or contingent?

Whether communities converge on a predictable climax or follow contingent paths shaped by chance arrival order and disturbance history remains debated, with priority effects and alternative stable states arguing for contingency.

Key figures

• Frederic Clements
• Henry Gleason
• Joseph Connell
• Ralph Slatyer

Seminal works

• begon2006
• connell1977
• clements1916

Frequently asked questions

What is the difference between primary and secondary succession?

Primary succession begins on substrates with no prior soil or biota, such as lava flows or glacial till, whereas secondary succession follows a disturbance that leaves soil and some organisms behind, such as after a fire or abandoned field.

What is a climax community?

A climax community is the relatively stable, self-perpetuating assemblage that classical theory predicted as the endpoint of succession, though modern ecology treats such endpoints as variable and disturbance-dependent rather than fixed.