Ecological Succession

Question 1

What is 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 are the types of ecological succession?

Answer 2

• primary succession
• secondary succession

Question 3

Where does primary succession begin?

Answer 3

• on sites that have not previously had plants growing on them
• e.g. beaches, ponds, bare rock

Question 4

Where does secondary succession begin?

Answer 4

• in areas where a disturbance removes some or all species but the soil remains

Question 5

What are the characteristics of community structure?

Answer 5

• not static
• determined over time by succession that takes place as a result of certain factors

Question 6

What determines community structure?

Answer 6

• disturbances
• competitive interactions

Question 7

What are the kind of disturbances that influence community structure caused by?

Answer 7

• physical disasters (e.g. storms, floods, fires)
• humans or animals (e.g. abandoned crop field, overgrazed area, logged forest)
• climate change

Question 8

How do disturbances determine community structure?

Answer 8

• creates opportunities for new species to move in
• new species alter the character of the community
• creating an environment suitable to even newer species

Question 9

What are the competitive interactions that influence community structure?

Answer 9

• competition
• predation

Question 10

What are the stages of ecological succession?

Answer 10

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

Question 11

Where do pioneer species grow best?

Answer 11

• bare ground conditions
• where there is little competition for space and resources

Question 12

What are the features of pioneer species?

Answer 12

• hardy
• establish rapidly
• have spores or seeds that can disperse over long distances
• do now grow in shade

Question 13

Why do pioneer species need to be hardy?

Answer 13

• to withstand extreme variations in temperature and moisture

Question 14

What do pioneer species do?

Answer 14

• prepare the surroundings for later colonists
• by altering the biotic and abiotic environment

Question 15

How do pioneer species prepare the surroundings for later colonists?

Answer 15

• build-up, stabilise and enrich the soil
• alter the amount of light available by providing shade

Question 16

What is an example of a floral pioneer species involved in primary succession?

Answer 16

• lichens

Question 17

How are lichens beneficial in primary succession?

Answer 17

• don’t need soil
• help to form soil as lichens and physical weathering break down rocks into smaller pieces
• add small amounts of organic matter to newly formed soil when they die and decompose

Question 18

What plants follow lichens in the pioneer species stage?

Answer 18

• mosses and other simple plants

Question 19

What are examples of faunal pioneer species?

Answer 19

• mites
• ants
• spiders
• small herbivores
• other decomposers such as earthworms

Question 20

When does secondary succession in the pioneer species stage occur?

Answer 20

• when the soil layer thickens

Question 21

What are the pioneer species of a secondary succession?

Answer 21

• annuals (herbs and weeds) are the first to appear after a disturbance
• grasses and perennials appear a year or so later
• in forest gaps or wetter sites a tangle of climbers develops

Question 22

Why do ecological conditions change and lead to the intermediate species stage?

Answer 22

• the soil can hold more water and is more fertile
• temperatures are less extreme as there is more shade

Question 23

What happens in the intermediate species stage as the soil builds up?

Answer 23

• small non-woody herbaceous species give way to small hardy woody plant species
• these turn into larger woody shrubs and bushes that are much slower growing
• grasses remain

Question 24

What animals become part of the community during the intermediate species stage?

Answer 24

• larger herbivores (hares, small antelope)
• small carnivores (caracal, wild cats)
• snakes
• raptors

Question 25

How do the intermediate species affect the communities?

Answer 25

• they make the communities more structurally complex

Question 26

What is the climax community stage?

Answer 26

• the last semi-stable stage
• endpoint of succession

Question 27

How do climax communities vary?

Answer 27

• large trees in a forest biome
• or grasses and Acacia trees in a Savannah biome
• dwarf, succulent shrubs in succulent karoo biome

Question 28

What are the characteristics of animal species in the climax community?

Answer 28

• most diverse
• include large herbivores and carnivores

Question 29

How is everything in a state of transition?

Answer 29

• future disturbances can cause the species of a community to change
• e.g. higher rainfall

Question 30

What environmental fluctuations determine an endpoint to a community?

Answer 30

• rainfall
• overgrazing
• draining of wetlands
• climate change
• invasion by alien species

Question 31

How does rainfall determine successional endpoints?

Answer 31

• amount of rain is the most important factor
• e.g. if rainfall is more than 1200 mm/year the endpoint will be a forest community
• e.g. prolonged drought means species able to withstand drier conditions will dominate and change the character of a forest community to a grassland or savannah endpoint

Question 32

How does overgrazing change a community?

Answer 32

• grazers often choose one grass species, which changes the composition of the climax communities in the grassland biome

Question 33

How does the draining of wetlands affect successional endpoints?

Answer 33

• permanently alters the environments
• resulting in the disappearance of wetland climax species

Question 34

How does climate change affect successional endpoints?

Answer 34

• climate change means some areas will get wetter and some will get drier
• changing grasslands into forest communities and subsequently changing the climax communities

Question 35

How does invasion by alien species affect successional endpoints?

Answer 35

• they replace the once dominant species in climax communities