Populations In Ecosystems - Succession

- Succession - 

Succession occurs over a number of steps: 

At each of these new stages the species colonies and alter the environment at each stage. This could go either one of two ways:

1. The environment is made less suitable for the existing species. Which means that the new species may out compete the existing species as they may have adapted to the environment // would have a given advantage. 
2. The environment is made more suitable for different species that have different adaptations. This species may be out competed by the better adapted new species. 

Stages of succession 

1. Single organisms rapidly multiple through asexual reproduction // to build the population. 
2. A vast quantity of wind-dispersed seeds/spores produced // reach isolated areas 
3. Rapid germination of seeds // do not require a period of dormancy
4. The ability to photosynthesise // light = available, other sources of food = not available 
5. Soil has few or no nutrients // able to fix nitrogen from the air 
6. tolerance/adaptations to the extreme conditions. 

There would need to be a stable state to find a balance in the equilibrium of species with few, if any, new species replacing those have become established. In this state there are many species that flourish // increase in biodiversity = climax community. 

The climax community is determined by the limiting abiotic factors. 

For examples - trees are unlikely to grow on mountains as the conditions are too cold and there is little soil for the roots to bury itself in to collect the required nutrients for the tree - especially at the start of succession. 

During succession there are a number of common features that occur 

• Non-living (Abiotic) environment becomes less hostile - soil forms // retains water & nutrients. 

• A greater number and variety of habitats and niches - this produces 

• Increased biodiversity - different species occupy these habitats // reaches peak in mid-succession // decreases as climax community is reached - in other words the dominant species out compete the pioneer species. 

• More complex food webs 

• Increase in biomass // during mid-succession. 

Secondary succession = when land has already sustained life however due to land clearance for agriculture for example, forest fire, the ecosystem returns to it's climax community // occurs more rapidly. Land has been changed/altered in a way that results in the climax community being different. 

This is an example of an ecological succession : ↓