Module 6 - Chapter 23 Ecosystems Flashcards Preview

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Flashcards in Module 6 - Chapter 23 Ecosystems Deck (115)
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Primary succession

The progressive placement of species on a newly formed or exposed area of uncolonised land where no previous organic material (such as soil) was present.


Give examples of starting land for primary succession

Newly formed sand dunes, bare rock, river deltas, glaciers


How does biomass change in primary succession? Why?

Increases because plants at later stages are larger than plants at earlier stages


Secondary succession

The replacement of one dominant type of species on land which has organic material (existing soil) but no living plant or animal species, some seeds may remain viable in the soil which plants can then develop from.

All previous living matter has been eradicated by natural disasters or biotic interventions such as forest fires.


Stage the seres of succession in order for primary succession

1) Barren land
2) pioneer community
3) intermediate community
4) climax community


Stage the seres of succession in order for secondary succession

1) intermediate community
2) climax community


How are primary and secondary succession different in the seres of succession? Why is secondary succession faster?

Primary succession begins from barren land and progresses to climax community.
Secondary succession begins with tertiary colonisers and scrubland in the intermediate community, biotic intervention occurs then recolonisation before reaching the climax community.

There are less seres in secondary succession so it’s quicker


Effects of the pioneer community in an uncolonised area

- stabilise the environment
- increase the humus content of the soil
- increase nitrogen content of the soil by nitrogen fixing
-increase soil depth (formation of soil)



What is the pioneer community?

The pioneer species/colonisers are the first organisms to arrive at and colonise an area of newly formed or exposed land. They initiate the development of an ecosystem by changing the habitat and allowing different species to colonise.

This is possible due to their adaptations which are specialised to take advantage of the environment.


Adaptations of the pioneer community

•Able to produce large quantities of rapidly germinating seeds to reproduce

•are able to photosynthesise

•contain nitrogen-fixing bacteria to enrich the soil with minerals

•wind-pollination increases the likelihood of reproduction because insects are often not present.


How are the pioneer species introduced to the environment?

As wind-carried spores or seeds from nearby land or animals (including bird droppings)


Examples of pioneer species

Algae, lichen


What stages can the intermediate community be divided into?

Secondary colonisers, tertiary colonisers and scrubland


What do the secondary colonisers do?

Arise after the land is able to support their growth.

Soil is formed from weathered rock and the death of pioneer species enriches the soil when they decompose, releasing organic products (humus). The humus is able to sustain the secondary colonisers when they arrive as spores/seeds due to containing minerals, nitrates and retaining some water.


Example of secondary colonisers



What do tertiary colonisers do?

Colonise the land once the conditions of the environment have improved to be able to supply the plants with sufficient water and minerals from the environment. they have a waxy cuticle to prevent water loss, maximising water retention.


Examples of tertiary colonisers

Grasses, ferns


How does scrubland arise?

Increased soil depth with a higher humus content is able to retain more water. These changes allow scrubland to grow in the more favourable conditions.


Examples of scrubland

Grasses, shrubs, small trees


Changes to the soil during succession

•pH decreases as humus content increases (humus is acidic)
•soil depth increases - due to weathering of rock
•rocks broken down by root growth
•soil aerated (by roots)


What is the climax community?

The final stage of succession

consists of the most dominant and well-adapted species for the environment so the community is stable (in equilibrium with the environment) and little change is observed over time.


When is biodiversity greatest during succession?

In mid-succession (intermediate community) before decreasing as the climax community develops.

The climax community has decreased biodiversity because the more adapted and dominant species outcompete the earlier pioneer and secondary colonisers.

the pioneer communities are often less stable because they are subject to greater succession.


Example of climax community



What is deflected successsion?

When human activities prevent the climax community from being reached by stopping the natural succession process. A subclimax (plagioclimax) is reached.
The environment is changed so a different end product is formed which is not part of the natural progression to the climax community.


What is a plagioclimax?

A stage in succession when the natural climax community is prevented from forming (an artificial climax)


Example of a plagioclimax



ways in which deflected succession could be caused?

grazing of animals - eating/trampling of seedlings of shrubs and trees prevents the development of grassland to scrubland

mowing of grass

application of fertiliser

humans burning forests to clear land - destroying the climax community and scrubland develops


what is autogenic succession?

when the changes to the environment are brought about by the plants themselves


what is allogenic succession?

when changes to the environment are brought about by external factors, e.g. rising sea level caused by flooding


definition for ecosystem

a defined area and all of the communities within it. consists of abiotic and biotic components and encompasses all of their interactions