19.6 - Succession Flashcards
Ecosystems are dynamic. How does this relate to the term succession
- This means that they change day to day as populations fluctuate, sometimes slowly and sometimes very rapidly.
- Succession is the term used to describe these changes, over time, in the species that occupy a particular area.
Succession takes place in a series of stages. At each stage what might happen
- new species colonise the area and these may change the environment.
- These species may alter the environment
How may new species alter the environment
1) less suitable for the existing species. As a result the new species may out-compete the existing one and so take over a given area.
2) more suitable for other species with different adaptations. As a result this species may be out-competed by the better adapted new species
- In this way there is a series of successional changes which alter the abiotic environment.
- These alterations can result in a less hostile environment that makes it easier for other species to survive.
- As a consequence new communities are formed and biodiversity may be changed and/or increased.
What are pioneer species
- at first stage of succession there is colonisation of an inhospitable environment by organisms called pioneer species.
- Pioneer species make up a pioneer community and often have features that suit them to colonisation.
What features to pioneer species have that adapt them for colonisation
- asexual reproduction so that a single organism can rapidly multiply to build up a population.
- the production of vast quantities of wind-dispersed seeds or spores, so they can easily reach isolated situations such as volcanic islands
- rapid germination of seeds on arrival as they do not require a period of dormancy
- the ability to photosynthesise, as light is normally available but other food is not. They are therefore not dependent on animal species
- the ability to fix nitrogen from the atmosphere because, even if there is soil, it has few or no nutrients
- tolerance to extreme conditions.
Give an example of a pioneer organism
- Imagine an area of bare rock.
- One of the few kinds of organism capable of surviving on such an inhospitable area is lichens.
- Lichens are therefore pioneer species because they can survive considerable drying out.
- In time, weathering of the base rock by the action of the lichens produces sand or soil, although this in itself cannot support other plants.
- However, as the lichens die and decompose they release sufficient nutrients to support a community of small plants.
- In this way the lichens change the abiotic environment by creating soil and nutrients for the organisms that follow.
- therefore the next stage in succession follows (for this example it would be moss)
In the UK the ultimate community is most likely to be….
- deciduous oak woodland.
- This stable state comprises a balanced equilibrium of species with few, if any, new species replacing those that have become established.
- In this state, many species flourish and there is much biodiversity (climax community)
What is a climax community
- when many species flourish and there is much biodiversity.
- it remains more or less stable over a long period of time.
- This community consists of animals as well as plants
During any succession there are a number of common features that emerge, such as
- the non-living (abiotic) environment becomes less hostile, for example, soil forms (which helps retain water) nutrients are more plentiful, and plants provide shelter from the wind. This leads to:
- a greater number and variety of habitats and niches that in turn produce:
- increased biodiversity as different species occupy these habitats. This is especially evident in the early stages, reaching a peak in mid-succession, but decreasing as the climax community is reached. The decrease is due to dominant species out-competing pioneer and other species, leading to their elimination from the community. With increased biodiversity comes:
- more complex food webs, leading to:
- increased biomass, especially during mid-succession
The climax community is determined by…
- the limiting abiotic factor.
- e.g., trees may not develop on very high mountains because it is too cold, too windy, or the soil layer is too thin (especially at the start of a succession).
It is ______ _______ such as climate that determine the ________ species of the community
- Abiotic factors
- dominant
What other type of succession occurs (not the one about pioneer species)
- when land that has already sustained life is suddenly altered.
- This may be the result of land clearance for agriculture or a forest fire.
- called secondary succession
Describe the steps to secondary succession
State the general name given to the first organisms to colonise bare land,
pioneer species
Describe how changes in the environment lead to increased biodiversity during succession
- primary colonisers (pioneer species) photosynthesise and fix nitrogen
- these die and form a soil with nutrients
- further colonisers can survive in this soil + environment is a little less hostile + more habitats and food sources available
- other species are able to survive
- increased biodiversity
Using your knowledge of the nitrogen cycle, explain haw nitrogen from the atmosphere becomes incorporated into the soil, causing its level to increase during the first 100 years after the glacier retreats.
- Nitrogen from the atmosphere is fixed into compounds, e.g. proteins and amino acids by the nitrogen-fixing species (lichens, Dryas and alder).
- When these die or shed their leaves this nitrogen is released when decomposers break them down into ammonium compounds (ammonification) which are then broken down by nitrifying bacteria into nitrites and nitrates.
Suggest two reasons for the fall in soil nitrogen levels after 150 years
- More nitrogen is being absorbed by the increased biomass of the plants.
- The nitrogenfixing lichens, Dryas and alder have been replaced by spruce that does not fix nitrogen therefore less nitrogen is being added to the soil.
