Succession Flashcards
Define succession
Term used to describe changes, over time, in the species that occupy a particular area
In each stage of succession, a species colonises the area and may alter the environment in a way that makes it:
Less suitable for existing species- new species may out compete existing one
More suitable for other species with different adaptions- this species may be out competed by the better adapted new species
How are new communities formed and biodiversity changed or increased?
A series of successional changes alters the abiotic environment
These changes can make the environment less hostile
Making it easier for other species to survive
Therefore new communities formed and biodiversity increased/changed
Define Pioneer species
General name given to the first organisms to colonise bare land
Organisms that colonise an inhospitable environment
What features do pioneer species have that make them suited to colonisation?
Asexual reproduction so a single organism can rapidly multiply and build up population
Production of vast quantities of wind dispersed seeds or spores so they can easily reach isolated situations
Rapid germination of seeds on arrival
The ability to photosynthesise- so not dependant on animals
Ability to fix nitrogen from the atmosphere because if there is soil it will have few or no nutrients
Tolerance to extreme conditions
Give an example of a pioneer species
Lichen can survive on an area of bare rock
What happens to the soil when pioneer communities die?
Some organic material is released into the soil when they die. This allows recycling to start and increases mineral ions in the soil- allows other species of plants to grow
How do lichen make the environment less hostile
When they die and decompose they release sufficient nutrients to support a community of small plants - therefore they have changed the abiotic environment by creating soil and nutrients for next organisms
How do lichen produce sand/ soil?
Lichen colonise bare rock
By weathering the base rock, sand or soil is produced
Define climax community
The stable, final stage of succession
Food chains that develop into complex food webs lead to more stable communities.
This stable state compromises a balanced equilibrium of species with few new species replacing those that have become established
In this state many species flourish and there is much more biodiversity
Therefore a climax community stays stable over a long period of time
During any succession there are a number of common features that emerge:
The abiotic environment becomes less hostile
A greater number and variety of habitats and niches
So Increased biodiversity- as diff species occupy these habitats
This means more complex food webs
Leads to increased biomass
How can the abiotic environment become less hostile
Eg Soil forms (which helps to retain water) so nutrients are more plentiful and plants provide shelter from the wind
Climax community are determined by?
Climax communities are in a stable equilibrium with the prevailing climate
It is limiting abiotic factors that determine the dominant species of the community
What is secondary succession
Occurs when land that has already sustained life is suddenly altered eg land clearance for agriculture
The ecosystem returns to its climax community the same as primary succession but more rapidly
Why is secondary succession faster than primary succession
The soil already exists in which spores and seeds often remain alive in the soil and there is an influx of animals and plants through migration and dispersal from the surrounding area
