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8.12. Ecological successions

Ecological successions. The evolution of ecosystems

The ecosystems are dynamic, since both the communities that form it as the biotope undergo changes over time.
An ecological succession is a process of change, continuous and slow, of the ecosystem as a consequence of the variations that occur in the environment and in the populations that form it.
Two types of ecological successions are distinguished:

Primary ecological succession

It is the one that occurs when the ecosystem starts naturally in a newly created environment that has not been colonized by living beings. For example, when volcanic soils, newly formed natural lakes, dunes, new volcanic island, etc. are colonized.

Sucesión ecológica primaria

By Joshfn (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Secondary ecological succession

It occurs in an area that was already inhabited by communities but which, due to natural or human causes, have been modified. For example, an abandoned farm field, a forest after a fire, etc.

Sucesión ecológica secundaria

By Katelyn Murphy (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Characteristics of a succession

All ecological successions, under natural conditions, occur in a similar way. It is a long process that can last up to hundreds of years, characterized by:
  • Increase in biodiversity. There are more and more different species, some replacing others, creating a greater number of ecological niches.
  • Increase in biomass. As the succession progresses, the species are replaced by others of greater mass and volume.
  • Increase in ecosystem complexity. There are more and more species and a greater number of relationships between organisms, creating complex food chains and webs and other interspecific relationships.
  • Increased resistance to changes that may occur in the ecosystem. The ecosystem has self-regulatory mechanisms that allow it to resist any disturbances that occur.

Phases of an ecological succession

The tendency of an ecological succession is to gain complexity until it reaches its maximum degree of stability or climax. The characteristic stages of a primary ecological succession are:

Initial phase

In an area that has not yet created the ground, setting occurs pioneers or opportunistic species s . Lichens, mosses, fungi and algae, simple organisms that decompose bedrock by weathering to transform it and create the components of the soil.

Middle phase

When the soil is somewhat thicker, it is colonized by some herbaceous species that generate roots and contribute organic matter to the soil, which allows the appearance of arthropodsworms, etc.

Ripening phase

When the soil has developed, larger plants, such as shrubs and trees, begin to develop, allowing other animal and plant species to appear in the ecosystem.

Final phase or climax

When the ecosystem has reached its maximum development, in which stable and balanced conditions exist between its components, the climax or state of maximum stability is reached.
In this phase the greatest diversity of species is reached. Specialist species appear , with a  very reduced ecological niche.

Alterations of ecological successions. Ecological regressions.

Although an ecosystem can remain in its climax stage for a long time, such as tropical forests, it is likely that there are alterations due to natural or human causes, which modify that situation.

Ecological regression is the process of change that occurs in the ecosystem that modifies the natural order of stages of an ecological succession, transforming it into a more immature ecosystem with less biodiversity.

After an ecological regression, a secondary ecological succession will begin.

Interactive activity: Ecological successions.