Download Factors affecting the variety of species in an ecosystem

Factors affecting the variety of
species in an ecosystem
Chapter 7
Species & Biodiversity
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Species:
- 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 10-100
million could exist)
Habitat, Niche & Adaptation
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Habitat
- 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
Distribution
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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
Stable Ecosystem
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Contains a wide variety of species
Including producers, consumers &
decomposers
All members of the community are
interdependent
Effects of grazing on species
variety
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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
Effect of pollution on species
variety
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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
Other pollution
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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
Effects of human activity – habitat
destruction
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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
Biodiversity in crisis
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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
Disruption of food webs
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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
Importance of biodiversity
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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
Importance of biodiversity
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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
Behavioural adaptations in
animals
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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
Competition between plants
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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)
Competition between animals
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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
Competition between animals
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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
Predator-prey interaction
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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