23.4 - Succession

Question 1

Define succession

Answer 1

Progressive change of a community over time, changes in habitat features, new species populate, habitat features change again, and a new species populates the area until a stable climax community is reached

Question 2

What are the types of succesion?

Answer 2

1. Primary Succession

• Occurs in an area of land that is newly formed or exposed (e.g. bare rock), no soil or organic material present
• Occurs when: volcanoes erupt, lava deposits > igneous rock cools and solidifies; Sand blown by wind and deposited making sand dunes; Silt and mud deposited at river estuaries; Glaciers retreat exposing rock

1. Secondary Succession
   * Occurs in area where soil is present, no animals or plants. E.g. bare earth after a forest fire

Question 3

What is seral stage?

Answer 3

• Each stage of succession is known as a seral stage
• Each seral stage has key species identified, which change abiotic factors (e.g. soil) to make it suitable for existence of subsequent existence

Seral Stage: Pioneer community, intermediate community, climax community.

Question 4

What is the pioneer community & what are pioneer species adaptations?

Answer 4

Primary succession occurs as pioneer species (e.g. algae, lichen) colonise an inhospitable environment – 1^st seral stage

• These species are spores or seeds carried by wind or dropped by birds.

Pioneer Species Adaptations

• Ability to produce large quantities of seeds/spores
• Rapidly germinating seeds
• Ability to photosynthesise to produce own energy
• Tolerance to extreme environments
• Nitrogen-fixing ability – adding to soil’s mineral content

Question 5

Give features of the intermediate community

Answer 5

• Weathering of bare rock produces the basis of soil (unable to support a species yet)
• Pioneer species die and decompose, organic product is secreted into the soil (content known as humus)
• Soil can now support plant growth, secondary colonisers, as it has minerals and can retain some water
• Environmental conditions become better, new plant species arrive, tertiary colonisers, plants have waxy cuticle to prevent from water loss – can survive without abundance of water, they obtain most of water & mineral salts from soil
• Rock is continually eroded, organic matter mass increases, organisms decompose, deeper more nutrient-rich soil, retains water
• Abiotic conditions more favourable for flowering plants

Question 6

Give features of the climax community

Answer 6

• Final seral stage – community is in a stable state – little change will occur over time
• Few dominant plant and animal species present
• Species which from climax community is dependent on climate
• As succession increases biodiversity increases, with a peak increase in biodiversity during mid-succession, in the climax community dominant species are present so biodiversity does not increase greatly

Question 7

What occurs during animal succession?

Answer 7

Primary consumers (insects, worms) are first to colonise an area and shelter under moss and lichen

They migrate from neighbouring areas, animal succession is therefore slower than plant succession

Secondary consumers arrive when suitable food sources establish and there is enough plant habitat to accommodate the species.

Question 8

What is deflected succession and define phagoclimax?

Answer 8

Human activity can halt natural succession, preventing the ecosystem from reaching climax community.

Phagoclimax – where succession is stopped artificially, the final succession phase name

Question 9

Give agricultural reasons for deflected succession.

Answer 9

• Grazing and trampling of vegetation by domestic animals
• Removing vegetation (shrub) to plant crop – crop becomes final community
• Burning – forest clearance – often leads to increase in biodiversity as it provides space and nutrient rich ash for species to grow