Ecological succession: Who starts it? (Pioneer species)

This is the third post in a series of posts where I seek to explain one of the most important concepts of Ecology-Ecological succession. I have previously discussed the process and the resulting ecological changes, as well as the end result(s) of the succession process. Now, let’s take a look at how it all starts…

The beginning

The succession process requires one environmental factor for it to begin; no life. The entire process starts in an area where there has never been any life before (called primary succession) or the existing life has been destroyed (called secondary succession).

In nature, we see secondary succession more often than primary succession. Existing communities can be destroyed by natural phenomena like fires, cyclones, diseases or by anthropogenic activities.

This bare area is first colonized by organisms specifically designed by nature to begin a community in such areas. They are called pioneer species.

Features of pioneer species

All pioneer species, plant or animal, have these capabilities that allow them to live in an area that is potentially inhospitable to other forms of life. These are-

  • They can withstand harsh environments.
  • They can germinate in a variety of environments.
  • They are strong light-demanders.
  • The have high dispersal rates.
  • They can survive prolonged periods of dormancy.

Interesting observation: These capabilities are strikingly similar to invasive species.

pioneer species के लिए चित्र परिणाम

These species modify their environment as they live and survive, and produce conditions for other organisms to come and start living in the area. The modifications include altering the abiotic conditions (like soil, temperature, etc) as well as biotic conditions (by aggregating into populations and attracting prey species, etc).

Are pioneer species autotrophs or heterotrophs?

They can be both, as I have mentioned earlier. Depending on whether the pioneer species is an autotroph or hetrotroph, the whole process of succession as well as the characteristics of the process tend to change.

  • Autoptrophic succession

This happens when the pioneer species are plants, blue-green algae or planktons (in case of aquatic environments). It is characterized by the constant dominance of autotrophs throughout the ecological succession process. The energy content as well as biomass content of the community remains high and continues to increase till climax community is reached.

  • Heteroptrophic succession

This happens when the pioneer species are bacteria or fungi, for instance. Here, the initial dominance in the community is of heterotrophs, although autotrophs catch up in later successional stages. The energy content and biomass of the resulting communities show a steady decrease till the climax community is reached.

How much of a controlling factor does pioneer species have on the climax community?

Pioneer species do have a say in which direction the ecological succession proceeds, but they have little control over what the climax community will look like. Climax is controlled solely by the environmental factors and sometimes, by the community composition immediately preceding it.

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