TOPIC 5 able to survive in harsh conditions
1. Succession –primary
- Pioneer species such as algae/lichens/mosses are the first organisms to colonise bare rock
- The pioneer species grows in little soil, so thin and shallow soil forms
- They alter/improve the conditions, making them less hostile by adding humus/nutrients
- Plants with short roots able to grow in the thin soil and displace the pioneer species as they
become better competitors
- Changes in soil structure enable trees/shrubs/grass to grow as next group colonisers
- The soil contains water and minerals as plants die and decay (decomposed by bacteria)
- Organic matter is released (carbon dioxide)
- Competition limits species present
- The community reaches an equilibrium resulting in a climax community
2. Secondary succession
- The reestablishment of community following disturbance
- Plants die by some type of disturbance e.g. forest fire
- Only soil present -roots and seeds left over begin to grow into plants
- Pioneer species like grass grow from soil
- Some pioneer species die and decay
- Soil becomes rich in minerals and water
- Changes in soil structure enable trees and shrubs to grow as next group colonisers
- The community reaches an equilibrium resulting in a climax community
3. Deflected succession: when the habitat is prevented from ever becoming a climax
community due to human intervention/influence, forest fire, grazing
4. Climax community
- Final stage of succession
- Self-sustaining/stable as same species present over long time
- Abiotic factors constant
- It has many species (includes both animals and plants) – interaction between species
- There is a balanced equilibrium of species
- There is one dominant species and co-dominant plant or animal species
- Stable if no changes happen to environment/human influence
o Succession: series of changes that occur to the composition of species in the
community of organisms present in an area over a period of time
o Second definition: colonization of an area by organisms and their gradual replacement
over time by more varied and productive species
o Habitat: place where an organism lives. Each habitat has a particular set of conditions
which support different organism. Within a habitat there may be a population of
organisms – abiotic part of an ecosystem
o Population: group of interbreeding individuals of the same species found in an area.
The various populations in a habitat make up a community. Biotic part of an ecosystem
o Ecosystem: the community in a habitat and the combined biotic and abiotic factors of
the habitat -a system in which all organisms interact with the physical environment
, Distribution of organisms in a habitat are controlled by biotic and abiotic factors:
1. Abiotic factors: non-living physical and chemical factors
- Temperature: photosynthesis/respiration – use a thermometer
- PH: enzymes –soil sample taken around roots –dry out soil samples
- Light: photosynthesis/seed germination –light probe/sensor
- Water content/moisture: moisture probe or rain gauge –collect water over a period of time
- Wavelength/colour of light
- Take several reading and get an average
- They are all controlled
- They are constant, so they do not interfere with any results obtained
2. Biotic factor: living factors
- Competition from other plants (food, water, light)
- Disease
- grazing
- trampling
- predation
- They are density dependent – the effects are related to the size of the population relative to
the area available
- VERY hard to control these factors
These factors need to be controlled during an investigation in order for the results to be scientifically
valid. Only ONE factor needs to be varied/not controlled à other factors need to be kept constant
(control variables)
Some extra exam questions:
Suggest advantages of growing crops of wheat in glasshouses with artificial lightning rather than
growing them in open field
- Crops can be grown out of season
- Plants can photosynthesise 24 hours a day
- Less physical damage from weather/animals/pests
- Controls easier -> control of other factors –carbon dioxide and temperature
Temperate VS boreal forests:
- Temperate: high levels of precipitation, humidity and trees
- Boreal: moderate precipitation, cold temperatures and few trees
1. Succession –primary
- Pioneer species such as algae/lichens/mosses are the first organisms to colonise bare rock
- The pioneer species grows in little soil, so thin and shallow soil forms
- They alter/improve the conditions, making them less hostile by adding humus/nutrients
- Plants with short roots able to grow in the thin soil and displace the pioneer species as they
become better competitors
- Changes in soil structure enable trees/shrubs/grass to grow as next group colonisers
- The soil contains water and minerals as plants die and decay (decomposed by bacteria)
- Organic matter is released (carbon dioxide)
- Competition limits species present
- The community reaches an equilibrium resulting in a climax community
2. Secondary succession
- The reestablishment of community following disturbance
- Plants die by some type of disturbance e.g. forest fire
- Only soil present -roots and seeds left over begin to grow into plants
- Pioneer species like grass grow from soil
- Some pioneer species die and decay
- Soil becomes rich in minerals and water
- Changes in soil structure enable trees and shrubs to grow as next group colonisers
- The community reaches an equilibrium resulting in a climax community
3. Deflected succession: when the habitat is prevented from ever becoming a climax
community due to human intervention/influence, forest fire, grazing
4. Climax community
- Final stage of succession
- Self-sustaining/stable as same species present over long time
- Abiotic factors constant
- It has many species (includes both animals and plants) – interaction between species
- There is a balanced equilibrium of species
- There is one dominant species and co-dominant plant or animal species
- Stable if no changes happen to environment/human influence
o Succession: series of changes that occur to the composition of species in the
community of organisms present in an area over a period of time
o Second definition: colonization of an area by organisms and their gradual replacement
over time by more varied and productive species
o Habitat: place where an organism lives. Each habitat has a particular set of conditions
which support different organism. Within a habitat there may be a population of
organisms – abiotic part of an ecosystem
o Population: group of interbreeding individuals of the same species found in an area.
The various populations in a habitat make up a community. Biotic part of an ecosystem
o Ecosystem: the community in a habitat and the combined biotic and abiotic factors of
the habitat -a system in which all organisms interact with the physical environment
, Distribution of organisms in a habitat are controlled by biotic and abiotic factors:
1. Abiotic factors: non-living physical and chemical factors
- Temperature: photosynthesis/respiration – use a thermometer
- PH: enzymes –soil sample taken around roots –dry out soil samples
- Light: photosynthesis/seed germination –light probe/sensor
- Water content/moisture: moisture probe or rain gauge –collect water over a period of time
- Wavelength/colour of light
- Take several reading and get an average
- They are all controlled
- They are constant, so they do not interfere with any results obtained
2. Biotic factor: living factors
- Competition from other plants (food, water, light)
- Disease
- grazing
- trampling
- predation
- They are density dependent – the effects are related to the size of the population relative to
the area available
- VERY hard to control these factors
These factors need to be controlled during an investigation in order for the results to be scientifically
valid. Only ONE factor needs to be varied/not controlled à other factors need to be kept constant
(control variables)
Some extra exam questions:
Suggest advantages of growing crops of wheat in glasshouses with artificial lightning rather than
growing them in open field
- Crops can be grown out of season
- Plants can photosynthesise 24 hours a day
- Less physical damage from weather/animals/pests
- Controls easier -> control of other factors –carbon dioxide and temperature
Temperate VS boreal forests:
- Temperate: high levels of precipitation, humidity and trees
- Boreal: moderate precipitation, cold temperatures and few trees
