1. Factors affecting the variety of species in an ecosystem
Chapter 7

2. Species & Biodiversity
- living organisms similar enough to interbreed & produce fertile offspring
Biodiversity:
- total variation between all living things on earth
- includes variation within a species
- and between different species
About 1.75 million species studied (BUT million could exist)

3. Habitat, Niche & Adaptation
- where an organism lives within an ecosystem
Niche
- the role a species plays within a community
To succeed in a community, organisms must be suited to their environment
- this often involves adaptation
- can be structural or behavioural

4. Distribution
An organisms adaptations will make it well, or poorly, suited to a habitat or niche
This will affect it’s distribution
The better it is suited, the more likely it will be found in that area
- Desert plants
- Mosquitoes
- Darwin’s Finches

5. Stable Ecosystem Contains a wide variety of species
Including producers, consumers & decomposers
All members of the community are interdependent

6. Effects of grazing on species variety
Grassland has many varieties of grass
Some are sturdy, others more delicate
- rabbits are unselective grazers
- they keep the sturdy grasses in check
- but if rabbits are removed, sturdy grasses drive out the delicate grasses
- variety of grasses is reduced
Sheep select to eat the sturdy grasses – help maintain biodiversity

7. Effect of pollution on species variety
Sulphur Dioxide (SO2)
Released by burning fossil fuels
Can damage plants & respiratory systems
- lichen have varying sensitivity to SO2
- more SO2, less lichen survive
SO2 (and nitrogen oxides) can also dissolve in water (e.g. rainwater)
- this leads to acid rain
- this falls on, and lowers the pH of, seawater, freshwater & soil

8. Other pollution Thermal Power stations use river water as a coolant
Water returned to the river is much warmer
Increases temperature causes a decrease in oxygen levels
Causes a decrease in variety of fish species
Sewage
If untreated sewage leaks into rivers, bacteria feed on it
They use up the oxygen in the water
Only a few freshwater species can survive in low oxygen
Most will die – decrease in species diversity

9. Effects of human activity – habitat destruction
Humans dominate the world ecosystem
Deforestation
Clearing of natural forest, without replacement
- CO2 levels increase
- soil becomes infertile
- flooding of low-lying areas
- river levels change, water becomes muddy
Desertification
- caused by over-use of land on the edge of a desert
- water levels drop, forests cleared, desert sands take over

10. Biodiversity in crisis
Life on earth has had many mass extinctions
Some species adapt to global changes, others don’t
Humans are causing extinctions to increases by 400 times
Many species wiped out by over-hunting & habitat destruction
There are also many endangered species

11. Disruption of food webs
Most food webs are finely balanced
If one organism in the web is lost, it can have a knock-on effect on others
If a food web is small, the effects are very severe
E.g. myxomatosis on rabbits
Larger webs have less severe effects

12. Importance of biodiversity
Aesthetics:
- natural beauty of the environment enriches life
Economics:
- Most species have 100’s/1000’s of genes
- These could potentially be used medicines, food, materials etc
- many potentially useful genes have yet to be discovered
Effect of selective breeding:
- increases weakness to environmental changes
- e.g. disease, global warming
- wild varieties could hold resistance to these changes

13. Importance of biodiversity
Opportunists:
- cockroaches, rats, weeds often over-run destroyed habitats
- more destroyed habitats = more opportunists
The U.N has pledged to:
- conserve biodiversity
- use biodiversity sensibly, ensure it lasts
- share the benefits of biodiversity to all nations

14. Behavioural adaptations in animals
Animals detect an environmental stimulus using receptors
E.g. sense organs
Internal communication (e.g. nervous system) makes a response
Carried out by effectors (e.g. muscles)
Different species will respond differently
Their particular behaviour will help them to adapt to the environment

15. Competition between plants
Plants will compete for:
- light, water, soil nutrients
Plants of the same species will have the same requirements
- competition will be intense
- sown seeds need to be carefully spread
Plants of different species will have different requirements (less intense)
But, some species can dominate at the expense of others
E.g. conifer trees (pine trees)

16. Competition between animals
Animals compete for:
- food, water, shelter, mates etc.
Within a species - competing will be very intense
Territoriality
- competition for a territory (e.g. robin/grouse)
- territory contains enough food for an animal, it’s mate & it’s young
- territory is defended by social signals
- territory will be defended aggressively near the centre, less so at the edges
- ensures population is well spaced out

17. Competition between animals
Between different species
Many different species occupy the same niche/habitat
Squirrels:
- Grey squirrel has become dominant over red squirrel
- Grey competes more aggressively for food
Trout:
- rainbow trout has dominated brown trout
Reducing competition:
- some species come to a compromise, rather than compete
- e.g. green & common cormorant

18. Predator-prey interaction
Increased no. of prey, leads to increased predation
As the no. of prey then decreases, competition gets more intense
So, eventually, the predators no. drop
This allows no. of prey to increase again