Ecological Succession Flashcards
What is ecological succession?
- a predictable pattern of gradual change over time in the types of species in a community following a disturbance
What are the types of ecological succession?
- primary succession
- secondary succession
Where does primary succession begin?
- on sites that have not previously had plants growing on them
- e.g. beaches, ponds, bare rock
Where does secondary succession begin?
- in areas where a disturbance removes some or all species but the soil remains
What are the characteristics of community structure?
- not static
- determined over time by succession that takes place as a result of certain factors
What determines community structure?
- disturbances
- competitive interactions
What are the kind of disturbances that influence community structure caused by?
- physical disasters (e.g. storms, floods, fires)
- humans or animals (e.g. abandoned crop field, overgrazed area, logged forest)
- climate change
How do disturbances determine community structure?
- creates opportunities for new species to move in
- new species alter the character of the community
- creating an environment suitable to even newer species
What are the competitive interactions that influence community structure?
- competition
- predation
What are the stages of ecological succession?
- Pioneer species stage
- Intermediate species stage
- Climax community
Where do pioneer species grow best?
- bare ground conditions
- where there is little competition for space and resources
What are the features of pioneer species?
- hardy
- establish rapidly
- have spores or seeds that can disperse over long distances
- do now grow in shade
Why do pioneer species need to be hardy?
- to withstand extreme variations in temperature and moisture
What do pioneer species do?
- prepare the surroundings for later colonists
- by altering the biotic and abiotic environment
How do pioneer species prepare the surroundings for later colonists?
- build-up, stabilise and enrich the soil
- alter the amount of light available by providing shade
What is an example of a floral pioneer species involved in primary succession?
- lichens
How are lichens beneficial in primary succession?
- 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
What plants follow lichens in the pioneer species stage?
- mosses and other simple plants
What are examples of faunal pioneer species?
- mites
- ants
- spiders
- small herbivores
- other decomposers such as earthworms
When does secondary succession in the pioneer species stage occur?
- when the soil layer thickens
What are the pioneer species of a secondary succession?
- 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
Why do ecological conditions change and lead to the intermediate species stage?
- the soil can hold more water and is more fertile
- temperatures are less extreme as there is more shade
What happens in the intermediate species stage as the soil builds up?
- 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
What animals become part of the community during the intermediate species stage?
- larger herbivores (hares, small antelope)
- small carnivores (caracal, wild cats)
- snakes
- raptors
How do the intermediate species affect the communities?
- they make the communities more structurally complex
What is the climax community stage?
- the last semi-stable stage
- endpoint of succession
How do climax communities vary?
- large trees in a forest biome
- or grasses and Acacia trees in a Savannah biome
- dwarf, succulent shrubs in succulent karoo biome
What are the characteristics of animal species in the climax community?
- most diverse
- include large herbivores and carnivores
How is everything in a state of transition?
- future disturbances can cause the species of a community to change
- e.g. higher rainfall
What environmental fluctuations determine an endpoint to a community?
- rainfall
- overgrazing
- draining of wetlands
- climate change
- invasion by alien species
How does rainfall determine successional endpoints?
- 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
How does overgrazing change a community?
- grazers often choose one grass species, which changes the composition of the climax communities in the grassland biome
How does the draining of wetlands affect successional endpoints?
- permanently alters the environments
- resulting in the disappearance of wetland climax species
How does climate change affect successional endpoints?
- climate change means some areas will get wetter and some will get drier
- changing grasslands into forest communities and subsequently changing the climax communities
How does invasion by alien species affect successional endpoints?
- they replace the once dominant species in climax communities
