23.4 succession

what is succession

the process by which ecosystems change over time

2 types of succession

primary succession - this occurs on an area of land that has been newly formed or exposed such as bare rock .There is no soil or organic matter to begin with

secondary succession - this occurs on areas of land where soil is present, but it contains no plant or animal species. An example example would be the bare earth that remains after a forest fire

examples of primary succession

• volcanoes erupting, depositing lava - when lava cools are solidifies igneous rock is created

• sand is blown by the wind or deposited by the sea to create new sand dunes

• slit and mud are deposited at river estuaries

• glaciers retreat depositing rubble and exposed rock

the main serial stages of succession

pioneer community

intermediate community

climax community

pioneer community

they colonise inhospitable environments . These species arrive are spores or seeds carried by the wind from nearby land masses.

eg. algae and lichen

adaptations include;

• the ability to produce large quantities of seed or spores

• seeds that germinate rapidly

• the ability to photosynthesise and produce their own energy

• tolerance to extreme environments

• the ability to fix nitrogen from the atmosphere, so adding to the mineral content of the soil

intermediate community

• when the organisms of the pioneer species die, small organic products are released to the soil

• this organic component of the soil is known as humus

• secondary colonisers arrive as spores or seeds such as ferns

• as environmental conditions continue to improve, new species arrive called tertiary consumers. They have a waxy cuticle so they can survive without an abundance of water but need to obtain water and mineral salts form the soil

climax community

• the final serial stage

• the community is in a very stable state and will change very little over time

• there are normally a few dominant species

• biodiversity tends to peak in mid-succession and then tends to decrease due to dominant species out competing pioneer and over species, resulting in their elimination

animal succession

• primary consumers such as insects and worms are the first to colonise a new area - they must move in from neighbouring areas so animal succession is slower than plant succession

• secondary consumers will arrive once a suitable food source has been established and the existing plant cover will make habitats

• eventually larger organisms will colonise the area once the biotic conditions are favorable

deflated succession

human activities can halt succession. When succession is halted artificially, the final stage is known as plagioclimax

agriculture is one of the main reason deflected succession occurs:

• grazing and trampling of vegetation by domesticated animals - this results in large areas remaining as grassland

• removing existing vegetation to plant crops - this crop becomes the final community

• burning forests as a means of forest clearance - this often leads to a increase in biodiversity as it provides space and nutrient rich ash for other species to grow