Biomes
OCR
7.35-6
Tropical rain
forest
Tropical seasonal
forest
Temperate
deciduous forest
Temperate
deciduous
forest
Boreal forest
Tropical grassland / forest
ecotone (Bolivia)
Tropical grassland
(Bolivia)
Tropical
grassland =
savannah
(Tanzania)
Temperate grassland =
prairie
Tundra
Bare rock in montane
region (& boreal forest)
Cactus desert (Arizona)
Hot desert
Hyper-arid desert
Energy
OCR 7.32
There are 2 types of
cycle
Energy
Nutrients
Trophic Pyramids
Trophic or energy pyramids
show how energy is
transferred through an
ecosystem.
They
are
an
easily
accessible way of looking
at
whether
there
is
dynamic equilibrium, or
whether the system is
becoming unsustainable.
Trophic Pyramids
Sunlight energy fixed by
green plants is passed
through the ecosystem in
food chains and webs form
one trophic level to the
next. As energy is passed
through the system it is
stored at various trophic
levels.
The storage of
energy (I.e. the amount of
living matter present) is
referred to as Biomass or
Standing Crop.
Tertiary consumers /
top predators
OCR 7.31
Secondary
consumers
Primary
consumers
Primary
producers
Energy transfer OCR 7.30, 7.31,
7.37
Trophic Pyramids
Trophic
level 3
Loss of
energy
Secondary
consumer
Trophic
(Carnivore)
level 2
Primary consumer
Trophic
Loss of
(Herbivore)
level 1
biomass
Primary producer
(Plants)
Total biomass
Why does each successive Trophic
level get smaller?
• Energy is lost by: respiration, movement, reproduction
and growth.
• Transfer of energy is inefficient. Not everything is eaten
at each level so some is removed by detritivores. The
transfer of light energy to food energy is only 1% efficient.
• Not all energy can be metabolised efficiently at each
level and some is lost via defecation, removed by detritivores.
A few years ago, Animal rights protesters freed a
large number of mink from a farm and let them
run wild in the local woods. Mink are not
indigenous to this country and have no natural
predators. They are efficient killers and, like cats
and foxes, kill instinctively whether they need
food or not.
Q) If we assume our trophic pyramid is a UK
woodland ecosystem (although whether there are
any truly natural ones left is debatable). How
would the introduction of mink effect it?
Make sure you refer to the changes in terms of
energy transfer, and work through you example
carefully.
The addition of mink to a woodland
ecosystem
The massive
Loss of
energy
Loss of
biomass
Secondary
consumer
increase in
the
(Mink added)
number of
Primary consumer
carnivores
will
(Herbivore)
Primary producer
(Plants)
Total biomass
lead to the
reduction in
the
number of
herbivores
The addition of mink to a woodland
ecosystem
Q) Although the total
The primary
consumers
biomass of the plants
has increased. Is this
Secondary
likely to be sustainable
consumer
and are the plants that
(Mink added)
are increasing going to
will continue to
decrease
and this will lead to
an
increase in the total
be beneficial to the
biomass of the plants.
ecosystem?
Primary producer
(Plants)
Total biomass
The addition of mink to a woodland
ecosystem
The balance of plants in the ecosystem will be
Mink will eventually
irreversably altered. Pioneer species such as nettles
run out of food and
which are usually kept down by the herbivores
will grow shading out other less
a) die of starvation or
hardy plants and saplings.
b) move to another
They will also rapidly use up
ecosystem
nutrients and minerals from
the soil for their growth.
Most herbivores will
Some plants will not be able to
reproduce without the herbivores
eating their seeds.
Total biomass
be killed
What other factors will affect the
Trophic Pyramid?
1) Fertilisers (NPK) could increase production beyond that
which the land could manage and possibly lead to
eutrophication
2) Pesticides can reduce populations of organisms which could
have a knock on effect throughout the system
3) Deforestation can have a direct adverse effect on the area
4) Artificial maintenance of the ecosystem. For example burning
heather to allow grouse to feed on the young shoots.
Productivity OCR 7.37
Productivity > refers to the rate of energy production, normally
on an annual basis
Primary Productivity > refers to plant productivity
Secondary Productivity > refers to that produced by animals
Gross Productivity > is the total amount of energy fixed
Net Productivity > is the amount of energy left after losses of
respiration and growth are taken into account
Net Primary Productivity (NPP) is the amount of
energy made available by plants to animals at the
herbivore level
The nitrogen cycle
Nutrient
Cycles
Gershmels
Nutrient Cycles
OCR 7.39
Gershmel’s
Nutrient
Cycles
Nutrient Cycles
Gershmels nutrient cycles are
a simple way of showing how
nutrients are transferred
around an ecosystem. They
can be represented in 2 ways:
STORES
FLOWS
What do all these represent? Page 38
The size of the arrows and the circles
indicates the amount of nutrients in that
store or transferred in flows in the system
There are
3 types of
store
Biomass (total mass of
living material)
Litter
Soil
Case Study Tropical Rainforest Ecosystem
Look at the diagram below and explain :
a) How the nutrients are being cycled
b) Why the removal of the rainforest would be so
Detrimental – human impact
Precipitation
Biomass
Dead matter
Uptake by plant roots
Litter
Runoff
Decomposers
Leaching
Soil
Removal of
minerals
Tropical rain forest
•biomass is
main store
•rapid
transfer
between
stores and
environment
Nutrient Cycle
The nutrient cycle is easily disrupted here – it is
a closed system
Once the vegetation is removed, nutrients are
quickly removed from the system - creating
infertile conditions - even deserts
Human Impact: Rainforest Ecosystem
after deforestation
Harvest
Trees removed and logged
Precipitation
Crop
Biomass
The removal
of trees
decreases
Litter
interception and
Ash
increases
runoff
Depletion of
Increased runoff nutrients in soil
Increased leaching
Case Study Tropical Rainforest
Ecosystem
Human Impact:
200 million people live in rainforests
Demand for timber / cleared land
1 Acre of rainforest is lost per second – 74 species are
Lost every day
Eg 5-15% of Madagascar’s GNP is lost each year
through soil erosion, flooding of rice paddies and silting
of electricity turbines
Case Study:
Temperate
Deciduous
Forest
Case Study Temperate
Deciduous Forest
Explain the nutrient
flow in a deciduous
forest ecosystem
OCR 7.40
Case Study Temperate Deciduous Forest
Precipitation
Biomass
Litter
Soil
Run-off
Leaching
Weathering
Temperate deciduous forest
•balance
between
stores
•moderate
transfers
between
stores
Case Study Temperate Deciduous Forest
Why is there a large store of nutrients in the soil?
1. Slow growth in winter
2. A low density of vegetation compared with the
tropical rainforest
3. Uptake of nutrients is about 25% as efficient
as a tropical rainforest
Case Study Temperate Deciduous Forest
Why is there a larger store of nutrients in Litter?
•Deciduous leaves are shed in winter to retain
moisture, conserve nutrients, avoid damage by
snow and ice, strong cold winter winds, conserve
energy when the sun’s power is low.
•Decomposition is slow (by detritivores) >
nutrients return to the soil
Case Study Temperate Deciduous
Forest
Human Impact:
Clearing for agriculture - the input of leaf fall has been
replaced by chemical and organic fertilizers
Forests are heavily managed for recreation,
conservation, economic exploitation
Very few areas of natural forest remain
Conclusion
You should now be able to understand the importance of
the cycling of nutrients through the different types of
ecosystem and also the following;
a) How a complex ecosystem can be understood using nutrients
b) How mans influence can radically alter the flows and
stores
c) How these different ecosystems can lead to,
or rely on particular soil types
d) which stores dominate particular ecosystems
Psammosere
Macro-nutrients
Carbon
Oxygen
Hydrogen
Micro-Nutrients
Nitrogen
Magnesium
Sulphur
Phosphorous
At an ecosystem level nutrient cycling
is part of an open system.
At a global scale however the nutrients are
being continually cycled and recycled.
In this way they differ from energy or trophic
cycles and pyramids where the energy arrives
from the sun and is eventually lost as heat
energy into space.
Boreal forest (taiga)
•litter is
main store
(needles)
•little
transfer
between
stores
Temperate coniferous forest
A) Why is the litter store so large?
B) Why are the flows so small?
C) What sort of soil would you expect here?