Topic 7—C:populations and ecosystems-4. Succession Flashcards
Definition of dynamic
- constantly changing (e.g. Ecosystems.)
Definition of succession
- It is the process by which an ecosystem changes over time
What happens at each stage of succession?
The plant and animal communities in an area slowly change the environmental conditions (e.g. By making the soil more fertile) making the conditions more suitable for other species with different adaptations.
What happens when the biotic conditions change?
- The abiotic conditions change which causes one community of organisms to be succeeded (replaced) by another
What are the two main types of succession?
- Primary succession.
- Secondary succession.
Where does primary succession happen on?
- land that’s been nearly formed or exposed
E.g. Where a volcano has an erupted to form a new rock surface or where sea level has dropped exposing a new area of land. - There’s no soil or organic material to start with
I.e. Just Bare rock
When does primary succession start?
- When species colonise a new land surface
- Seeds and spores are blown by the wind and begin to grow
What is the first species to colonise the area called?
- Pioneer species
What are the abiotic conditions like in primary succession?
- They are hostile (harsh) and only pioneer species can grow because they’re specially adapted to cope with the harsh conditions
Examples of hostile abiotic conditions
- There is limited water available because there is no soil to retain water
- There are a few minerals or nutrients because there’s no soil
- There may be high light intensity, exposure to wind and rain, and fluctuating temperatures because the area is directly exposed to the sun and the elements
Examples of pioneer species
- marram grass can grow on Sands near the sea because it has deep roots to get water and can tolerate the salty environment
- lichens are organisms usually made up of fungus and an alga. They’re able to survive in conditions because the fungus secretes acids which erode the rock releasing minerals.
- Shrubs of the calligonum Genus pioneer species that can grow in areas that experience periodic drought
What do pioneer species change?
- the abiotic conditions
- they die and microorganisms decompose the dead organic material which forms a basic soil
- this makes conditions less hostile e.g. the basic soil helps to retain water, so new organisms with different adaptations can move in and grow
What happens to the new organisms?
- they die and are decomposed
- this adds more organic material making the soil deeper and richer in minerals such as nitrates
- nitrogen fixing bacteria turn nitrogen from the atmosphere into ammonia
- this forms ammonium ions In solution that can be used by plants
- this means larger plants like shrubs can start to grow in the deeper soil, which retains even more water and contains more nutrients
- some new species may change the environment so that it becomes less suitable for the previous species
Later stages of succession
- at each stage, different plants and animals that are better adapted for the improved conditions move in, out-compete the plants and animals that are already there and become the dominant species in the ecosystem
- the dominant species are the ones which cause the most change to the abiotic environment making it more suitable for other species
- as succession goes on, the ecosystem becomes more complex
- new species move in alongside existing species which means that biodiversity increases
- plants create more habitats for animals
- the abiotic conditions become less hostile and the amount of biomass increases
- eventually these changes result in a climax community
- it wont change much more-its in a steady state
Definition of climax community
- the ecosystem is supporting the largest and most complex community of plants and animals it can
Primary succession (example)
- Bare rock lacks soil, is exposed to strong winds and has periods of drought.
- Lichens (the pioneer species) are able to survive because they can grow in cracks to avoid the wind, break down rock to release minerals and are adapted to survive periods of drought - The lichens die and are decomposed helping to form a thin soil which thickens as more organic material is formed
- this means other materials such as mosses can grow - Larger plants that need more water can move in as the soil deepens e.g. grasses and small flowering plants
- the soil continues to deepen as the larger plants die and are decomposed - Shrubs, ferns and small trees begin to grow, out-competing the grasses and smaller plants to become the dominant species
- diversity increases - Finally the soil is deep and rich enough in nutrients to support large trees
- these become the dominant species and the climax community is formed
Secondary succession
- happens on land that’s been cleared of all the plants
- he soil still remains e.g. after a forest fire or where a forest has been cut down by humans
- the established community of species is usually destroyed, but without too much disturbance to the soil
- it can occur during any stage (including the climax community) at the pioneer stage
- process is similar to primary succession
- but because there is already a soil layer secondary succession starts at a later stage- and the pioneer species are larger plants e.g. shrubs
Human impacts on succession
- human activities can prevent succession, stopping a climax community from developing
- when succession is stopped artificially like this the climax community is called a plagioclimax
Example
A regularly mown grassy field wont develop shrubs and trees (woody plants), even if the climate of the ecosystem could support them
- the growing plants of the woody plants are cut off by the lawnmower so larger plants can’t establish themselves
- the longer the interval between mowing, the further succession can progress and the more diversity increases
- but with more frequent mowing, succession can’t progress and diversity will be lower- only the grasses can survive being mowed
- mowing doesn’t just affect plants it can affect the wider biodiversity of the area
E.g. removing the woody plants destroys habitats for insects decreasing the number of insect species
Climatic climax communities
- which species make up the climax community depends on what the climates like in a ecosystem
- the climax community for a particular climate is called its climatic climax
Examples
- in a temperate climate, e.g. the UK, there’s plenty of available water, mild temperatures and not much change between the seasons
The climatic climax will contain large trees because they can grow on in these conditions once deep soils have developed
- in a polar climate there’s not much available water, temperatures are low and there are massive changes between the seasons. Large trees wont ever be able to grow in these conditions so the climatic climax contains only herbs or shrubs, but it’s still the climax community
