Grade 12 Environmental Studies - Part 4 Ecological Succession

Question 1

Define ecological succession:

Answer 1

A predictable pattern of gradual change over time in the types of species in a community following a disturbance.

Question 2

What is a biological community?

Answer 2

Consists of all the populations of different species that live together in the same area.

Question 3

What are the types of succession?

Answer 3

Primary succession - begins on sites that have not previously had plants growing on them e.g. beaches, larva flows, severe landslips, ponds and bare rocks

Secondary succession = begins in areas where a disturbance removes some or all species but the soil remains

Question 4

What determines community structure?

Answer 4

Community structure is not static. It is determined over time by succession that takes place as a result of either or both of the following:

1. Disturbances caused by physical disaster, humans or animals or climate change = this creates opportunities for new species to move in.
2. Competitive interactions between organisms = e.g. competition, predation etc.

Question 5

List the stages in succession:

Answer 5

1. Pioneer species stage
2. Intermediate species stage
3. Climax community

Question 6

Bare ground conditions favour pioneer plant species (early successional). They grow where there is little competition for space and resources. Discuss the FEATURES of early pioneer species:

Answer 6

1. **Hardy **- must withstand extreme variations of temperature and moisture
2. Establish rapidly - often slow growing e.g. lichens. Have spores and seeds that can disperse over long distances e.g. tiny seeds with prachutes.
3. Do not grow in shade e.g. grass

Question 7

What is the benefit of pioneer species?

Answer 7

**Prepare the surroundings for later colonists **

• How? By altering the biotic and abiotic environment (biotic = living; abiotic = non-living)
• They build-up, stabilise and enrich soil
• Alter the amount of light available by providing shade

This now allows other species that are better suited to this modified habitat to replace the pioneer species.

Question 8

Describe primary succesion of floral pioneer species:

Answer 8

1. **Lichens **are first species to become established on rock after disturbance - they do not need soil to survive.
   Soil starts to form as lichens and physical weathering break down rocks into smaller pieces.
   lichens die - the decompose, adding smoil amounts of organic matter to newly formed soil.
2. Mosses and othe simple plants follow
3. Ferns, grasses and annuals arrive as soil layer thicken

Question 9

Describe primary succession of faunal pioneer species:

Answer 9

1. mites, ants and spiders
2. small herbivores (insects, rodents and small birds) and other decomposers such as earthworms and larvae move in when more food is available

Question 10

Briefly mention and discuss the pioneer species of a secondary succession:

Answer 10

1. Annuals (herbs and weeds) arrive first
2. **Grasses and perennials **appear
3. In forest gaps or wetter sites - a tangle of climbers

Question 11

Explain the intermediate species stage:

Answer 11

Ecological conditions change - soil can hold more water (more fertile) and temperatures are less extreme (more shade)
Thus greater variety of organisms can now move in.
* small non-woody herbacious species - give way to small hardy woody plants give way - to larger woody shrubs and bushes (slower growing) .
* Grasses remain as part of the community.
* **Larger herbivores ** (hares, small antelope) small carnivores (caracal, wild cats), snakes and raptors become part of community.

Now a more structurally complex community.

Question 12

Define climax community:

Answer 12

• Last semi-stable stage or endpoint of succession.
• They vary e.g. could be lare trees in a forest biome, or grasses and Acacia trees in Savannah, or dwarf succulents shrubs in Succulent karoo biome.
• Thus - depends on different biomes.
• Animal species - most diverse - include **large herviores and large carnivores. **

Question 13

What is meant by “everything is in a state of transition”?

Answer 13

Future disturbances - species of a community can change
e.g. higher rainfall in Karoo - can change succulent Karoo into grassland.
Human are destroying climax communities… rare
(think of Kruger National Park)

Question 14

Name the factors that determine an endpoint to a community?

Answer 14

1. Rainfall - MOST NB factor
2. Overgrazing
3. Draining of wetlands
4. Climate change
5. Invasion by alien
   (Read through discussion page 20 - 21 and study some example in the textbook)
   THEN complete Learning Activity 12 & 13