6.5.5(Succession)

What is meant by the term succession

• A progressive change in a community of organisms overtime

Describe how Succession occurs

• It takes place in a number of steps, each one called a seral stage (or sere)

• At each seral stage, key species can be identified that change the abiotic factors make it favourable for other subsequent species to exist

What is meant by primary succession?

• Primary succession is the process that occurs when newly formed or exposed land(with no soil and no species present) is gradually colonised by an increased number of species

Describe the process of succession

• A pioneer species comes and begins to grow. As they die and decompose, the dead organic matter forms a basic soil

• This allows for other small species such as grass and small plants, to come and grow in the basic soil. As these decompose and the new soil becomes deeper and more nutrient rich

• Larger plants now deposit their seeds and grow and decompose and provide a deeper soil

• Eventually the soil is sufficiently deep and contains enough nutrients and can hold enough water to support the growth of very large species

• The final community is formed containing different species of plant and animal and now considered new land- This is known as the climax community

Describe the features of a pioneer species

• Large quantities of wind-dispersed seeds/spores

• Rapid germination

• Photosynthetic

• Fix nitrogen

• Tolerate extreme conditions - Salty spray, drought

• They form a pioneer community

Describe the role of stabiliser species in succession

• They are species such as sea sandwort and sea couch grass which stabilise the growing dine through long underground stems

• Marram grass grows, as he sand gets deeper and the grass gets taller

• This stabilises the sand further

Describe how nutrients develop during succession

• As more plants grow, die and decay, organic matter builds up in the sand

• This adds nutrients such as nitrates and phosphates to the sand

• The dune becomes grey

describe the role of nitrogen fixers in succession

• At the top of the dune nitrogen fixer plants grow

• These contain nitrogen fixing bacteria in their root nodules

• Rhizobium species convert gaseous nitrogen into ammonium ions which are converted to nitrates for DNA and amino acids and used for plant growth

Describe how humans affect succession

• Human activity often prevents or interrupt the process of succession - Deflected succession

• As a result, this stops climax communities from developing.

• Instead the final stage that is formed is called plagioclimax

Describe how managing succession can be a advantage

• Preventing an area from reaching ts climax community can sometimes be a good thing

• This is because ecosystems at the intermediate stages of succession, where small plants, and grasses are present, often hold a distinct diversity of plant species that would no longer exist if the climax community was reached

Describe the process of water bodies becoming a habitat for many species

• Succession:

  • Pioneer species first colonise an area and grow

  • They then die and the dead organic matter forms basic soil

  • Environment is now less hostile

  • New species are now able to live in the area due to improved conditions, and outcompete the pioneer species

  • Change in biodiversity

  • New species are able to love in the area due to improved conditions and they are a better competitor so the previous species are outcompeted

  • This step keeps repeating until a climax community is reached