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. In this post, we take a look at the species responsible to initiate ecological succession: pioneer species.
What are pioneer species?
Organisms specifically adapted to colonize bare, lifeless areas and begin an ecological community are defined as pioneer species. 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).
When pioneer species begin the ecological succession in an area where there has never been any life before it is called primary succession. If it starts in a place where the existing life has been destroyed it is 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.
Features of pioneer species
All pioneer species—plant or animal—have 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.
- They reach reproductive maturity very quickly.
- The produce large number of seeds and have high dispersal rates.
- They can survive prolonged periods of dormancy.
Interesting observation: These capabilities are strikingly similar to invasive species.
Some common examples of pioneer species
During primary succession on land, fungi and lichen are the most common pioneer species. They break down minerals in the rock to form soil, which allow subsequent communities to colonize the area.
In secondary succession on land, such as after a fire or when trees topple in forests, tree species like alders, birches and chir pine and many grass species can begin the succession process.
In aquatic environments, phytoplankton (microscopic organisms that photosynthesize) are the common pioneer species.
Are pioneer species autotrophs or heterotrophs?
They can be both. 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.