Changes over ecosystems over time by primary and secondary succession

 

Distinguish between primary and secondary succession

 

Ecological successions are the changes in the abiotic (non-living) and biotic (living) factors in an ecosystem over time. It is because of this that some species gradually replace other species in one particular area.

 

Primary Succession

• Occurs when succession starts on entirely new land without any established soil – this may occur at river deltas, sand dunes or on exposed rock

• As the organisms, which first colonize a region à i.e. lichen (pioneer plants which decompose thin layers of rock) as these die and decompose, they establish a layer of soil for future organisms to utilize – this is the start to primary succession

• On exposed rock, lichen and moss may initially colonize the area and provide a layer of soil for seeds to germinate, increasing species diversity.

• Eventually, primary succession will lead to equilibrium

 

Secondary Succession

• Occurs when succession starts on existing soil following a natural or artificial disturbance of primary succession

• Secondary succession occurs faster as soil from primary succession already is present

• During secondary succession, dominance is usually achieved by the fastest growing plants

• An example of secondary succession is recolonization after a forest fire

 

Outline the changes in species diversity and production during primary succession

 

• Species diversity will increase as primary succession proceeds

• Primary succession begins on the foredune, where there is no soil, only sand.

  • Lyme grass (Leymus arenarious) à salt tolerant, fast growing, its roots help bind the sand and stabilize the dune

  • Marram grass (Ammophila arenaria) à has underground roots that spread sideways, goes through a growth spurt when covered with sand.

  • However, little diversity of plant life on the foredune

  • Yellow dune stage,

  •  Dune develops a thin layer of soil from years of marram grass plants living and dying. Now plants with even better binding roots invade the sand. Rabbits may be common species in this dune; their droppings additionally add nutrients to the soil.

  • Humus organic matter in the soul begins to build up as the original pioneer plants die and decay.

  • Community is complicated

  • Grey dune

  • Dune develops layers of humus from years of plants dying and decomposing.

  • Sand not deposited there

  • Thick shrubs being to grow on this dune

  • Mature dune

  • Supports a forest

  • Forest full of

  • Only a few species (lichen and moss) are capable of living in environments that have never sustained life before (pioneer species)

  • As these species alter the environment, it becomes more habitable, leading to a larger diversity of species colonizing the region

• Production – an increase in biomass or available energy – will also increase as primary succession proceeds

  • In early succession, there are few plants, so gross production and net production are low

  • As the number and density of plant species increases with more soil, productivity also becomes greater

 

Explain the effects of living organisms on the abiotic environment, with reference to the changes occurring during primary succession

 

• Abiotic à Nonliving, as in a abiotic factor, which is a nonliving physical and chemical attribute of a system, for example light, temperature, wind patterns, rocks, soil, pH, pressure etc. in an environment.

 

• Primary succession begins on new land, with pioneer species breaking down substrate to create organic soil

• As plant species colonize the area, the litter produced by their growth and their decomposing remains will cause the following changes:

 

• Organic matter increases à the organic compounds in soil that come from decomposing organisms (humus). Humus retains water better than sand and plant roots can easily absorb the water. It is not very dense and allows oxygen gas to reach the roots of plants.

 

• Soil accumulates à the layer of soil deepens due to the accumulation of humus over time. The humus also mixes with the sand to create a nutritious soil that holds water and oxygen.

 

• Soil erosion reduces à Plant roots hold the sand and then the soil in place. The different plants have a diversity of root structures that keep the sand and soil from eroding due to wind or water. This allows for the continued development of the soil.

 

• Soil structure becomes more complex à the mix of humus and sand creates a soil structure that holds and releases water and allows for oxygen to reach the roots of plants.  

 

• Minerals accumulate à the increase in humus increases the mineral content of the soil. Minerals in the living organisms are deposited in the soil as the organisms die and decompose.

 

• Mineral recycling increases à Increasing amounts and diversity of decomposers make the minerals in the humus available for absorption by the plant roots. The nutrients in the soil are continually recycled thorough the ecosystem by the decomposers.

 

• This will allow for the growth of larger plants, which will provide shade and reduce erosion through the binding action of their roots

 

Describe a primary succession in a named type of habitat. (3)

 

• Primary succession is an area or substrate, which has never had organisms before, previously there might have been organism, flora and fauna, but now has no longer been there.

• Consider new land formed from volcanic eruption

• Pioneer species, are the first ones to settle down, they are simple autotrophs

• They cause change in the environment e.g. through the creation of organic soil 

• This leads to gradual changes in ecosystems “successions”

• A climax ecosystem may be achieved 

a