Succession Flashcards
Define ‘succession’
The term used to describe changes to the species that occupy a particular area at a particular time within an ecosystem
What may cause succession of bare rock land be colonised?
- A glacier retreating and depositing rock
- Sand being piled into dunes by wind/sea
- Volcanoes erupting and depositing lava
- Lakes/ponds being created by land subsiding
- Silt and mud being deposited at river estuaries
Define ‘pioneer species’
A species that can colonise bare rock or ground - the first species that colonise the area
What features do pioneer species have that suit them to colonisation?
- The production of vast quantities of wind-dispersed seeds/spores so they can easily reach isolated situations such as volcanic islands
- Rapid germination of seeds on arrival they so not require a period of dormancy (growth/development where activity is temporarily stopped)
- The ability to photosynthesise as light is normally available but other ‘food’ is not - not dependant on animal species
- The ability to fix nitrogen from the atmosphere as it has few/no other nutrients even is there is soil present
- Tolerance to extreme weather conditions
Describe succession
A species colonise a new land surface (seeds/spores are blown by the wind and begin to grow) - known as the pioneer species. Only pioneer species grow because they are specialised to cope with the harsh conditions. The pioneer species change the abiotic conditions - they die and microorganisms decompose the dead organic material forming soil. The soil helps retain water meaning that new organisms can move in and grow - when these decompose it adds more organic matter to the soil making it deeper and richer in minerals therefore larger plants can grow.
At each stage the plants and animals become better adapted for the improved conditions
Define ‘climax community’
The last stage of succession - the ecosystem is supporting the largest and most complex community of plants and animals and is in a steady state so will not change much more
What common features emerge during succession?
- The non-living environment becomes less hostile - eg, soil forms so nutrients are more plentiful and plants provide shelter from the wind, leading to:
- A greater number and variety of habitats - that in turn produce:
- Increased biodiversity - different species occupy these habitats (climate increases then peaks during mid-succession but then decreases due to dominant species out-competing pioneer and other species) within increased biodiversity comes:
- More complex food webs - leading to:
- Increased biomass - especially during mid-succession when biodiversity peaks
What is another type of succession?
When land that has already sustained life is suddenly altered eg, due to a land clearance for agriculture or a forest fire
It returns to its climax community the same as described previously but is more rapid as spores and seeds often remain alive in the soil and there is an influx of animals and plants through dispersal and migration from surrounding areas
It does not begin with a pioneer species but with organisms from subsequent successional stages
The climax community will differ as the land has been altered in some way eg, fire
Define ‘conservation’
The management of the Earth’s natural resources in such a way that maximum use can be made in the future - involves active intervention by humans to maintain ecosystems and biodiversity
What are the main reasons for conservation?
- Ethical - other species have occupied the Earth far longer than we have and should be allowed to coexist with us - respect for living things is preferable to disregard for them
- Economic - living organisms contain a large gene pool so can make millions of substances which may be useful in the future - long-term productivity is greater if ecosystems are maintained in their natural balanced state
- Cultural and aesthetic - habitats and organisms enrich our lives and their variety adds interest to everyday life and inspires writers, poets, artists, composers etc who entertain and fulfil us
How can species in early habitats of succession be conserved?
Managing succession in a way that prevents a change to the next stage - if the factor preventing further succession is removed then the ecosystem develops naturally into its climatic climax (secondary succession)
