Download File - CAPE Biology Unit 1 Haughton XLCR 2013

ECOLOGY
OCTOBER 13, 2011
CAPE BIOLOGY UNIT II
MRS. HAUGHTON
TOPICS TODAY
1.
FOOD CHAINS/WEBS
2.
TROPHIC LEVEL DIAGRAMS
3.
FLOW / TRANSFER OF ENERGY
4.
EFFICIENCY OF ENERGY TRANSFER
5.
PYRAMIDS OF NUMBERS, BIOMASS AND ENERGY
6.
CARBON, NITROGEN, HYDROLOGICAL CYCLES
TODAY

Syllabus objectives: Energy Flow and
Nutrient Cycling 3.2 -3.7

Biological science pages 298-314 for extra
information.

Please see powerpoints on website.
Syllabus Objective 3.2

Discuss the way in which energy flows in an
ecosystem by way of food chains and food
webs.

Food webs to be emphasized.
FOOD CHAINS

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
The passage of energy in the form of food
Arrows used to represent the energy flow
Organisms feed on only one other organism at
a time
Illustration limited in showing what actually
occurs in nature
FOOD CHAINS
TERMS IN FOOD CHAIN
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Producer
Primary consumer (herbivore)
Secondary consumer (carnivore)
Tertiary consumer (carnivore)
Quaternary consumer (carnivore)
Complex consumer (carnivore)
Detritivores and decomposers on every level

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Producers: Organisms which convert some of the
energy from the sun into stored chemical energy
(usually plants).
Primary consumers: Organisms that obtain energy
by consuming producers. They are herbivores.
Secondary consumers: Organisms which obtain
energy by consuming primary consumers. They are
carnivores.
Decomposers: These organisms form the end point
of every food chain. They are bacteria or fungi that
obtain their energy by breaking down dead
organisms from the other trophic levels.
DETRITIVORES

Each description of a trophic level will
describe an organisms role in the ecosystem.
Organisms may occupy more than one trophic
level, (e.g. when acting as omnivores).
FOOD WEBS

1.
2.
3.
More complex than food chains. Advantages
include:
Show a more true depiction of how
organisms feed on more than one other
organism
Able to show omnivores.
Provides the basis for a more quantitative
study of energy flow and material exchange.
FOOD WEBS
FLOW OF ENERGY AND
MATERIALS


Figure 10.4 on page 302 shows that energy
flows in a straight line and as food is eaten,
some of the energy is gained and most of it is
lost by the organism as respiration and heat.
The figure also shows that simultaneously, the
nutrients or materials in each organism is
recycled at each trophic level by detritivores
and decomposers.
Syllabus Objective 3.3

Discuss the efficiency of energy transfer
between trophic levels.
TROPHIC LEVELS

There is usually no more than four or five
trophic levels because:

The numbers of organisms decreases as the
trophic levels increase
Energy from the previous trophic level
decreases as the number of levels increase

Transfer of energy between trophic
levels

Transfer of energy between trophic levels is
relatively inefficient. Energy is transferred
from one trophic level to another as organisms
are consumed.

In primary producers the main energy input
is from the solar energy. In a plant, not all of
the solar energy available actually makes it
into the leaf.
Transfer of energy between trophic
levels

There is loss of energy by
reflection from the leaf,
transmission through the leaf,
and because some of the energy
is the incorrect wavelength.

The energy that is taken up by
the producer is then fixed by
photosynthesis, although again a
proportion of this energy is lost
as it is used up during
photosynthetic reactions.
Transfer of energy between trophic
levels

Of the energy that is fixed
in photosynthesis some
will be used during
respiration whilst the
remaining energy is the
portion that is incorporated
into the biomass. It is the
energy that is incorporated
into the biomass that is
available for the next
trophic level.
Transfer of energy between trophic
levels

In the consumer a
further series of energy
losses occur. The
consumer will take in a
certain amount of
energy from the trophic
level beneath it.
Transfer of energy between trophic
levels

This energy intake does not
equal the amount of energy
available in the biomass of
this organism since feeding
is an inefficient process.
There will be a loss of
energy through the
production of urine and
faeces, as well as losses
through respiration and
heat loss. This leaves a
proportion of the energy
consumed to be
incorporated into the
biomass.
Transfer of energy between trophic
levels

It is generally accepted that
only around 10% of the
energy gained from the
previous trophic level is
passed on to the next level.
All other energy is lost as
described above. This
limits the number of
trophic levels in any food
chain.
EFFICIENCY OF ENERGY FLOW
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Sun is the main source of energy
100 % energy shines from it
40 % is reflected
15 % is absorbed and converted to atmospheric heat
45 % alone penetrates to the earth’s surface
Only 1-5 % of this is used in photosynthesis to make
organic substances
EFFICIENCY OF ENERGY FLOW
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Of this 1-5% converted to organic substances,
only 50-80% of the organic material remains
after being used by the plant for its life
processes.
On a global average, plants fix only 0.1% of
the energy supplied by the sun
This energy then passes on the herbivores,
then subsequent carnivores during feeding.
EFFICIENCY OF ENERGY FLOW
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Production ecology studies productivity
Gross primary productivity (GPP) is the rate at
which energy is stored in plants in the form of
organic substances.
20-25% of the GPP is used by the plant and the
remainder is called the net primary productivity
(NPP).
It is this energy that passes on the herbivores or
omnivores as they feed on the producer.
EFFICIENCY OF ENERGY FLOW
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Not all of the materials available in the food is used
by the consumer organisms for production.
Some energy is lost as heat in respiration and waste
during excretion and egestion.
Detritivores and decomposers feed on the waste and
eventually dead organisms
The energy remaining in the organisms afer they
have respired and excreted are available for the next
trophic level.
EFFICIENCY OF ENERGY FLOW
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Production in heterotrophs is called secondary
production.
The average efficiency of transfer of energy
from plants to herbivores is 10%
The average efficiency of transfer of energy
from animals to animals is 20%
EFFICIENCY OF ENERGY FLOW


Herbivores make less efficient use of their
food than carnivores because plants contain a
high proportion of indigestible cellulose and
lignin.
Energy lost through respiration cannot be
used by another organism, but that lost
through excreta can be.
EFFICIENCY OF ENERGY FLOW
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In a stable ecosystem, the biomass at the start
of the year will be the same at the end.
All energy that went into primary production
will pass through the trophic levels and none
retained in net production
A young ecosystem would retain some of the
energy input in the form of increased biomass
at the end of the year (growth)
EFFICIENCY OF ENERGY FLOW
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It is therefore obvious that eating plants is the
most efficient way of extracting energy from
the ecosystem
However, animal protein is a better source of
essential amino acids
Animal protein is also more easily digestible
(See diagram page 308)
EXAMPLES OF ENERGY
EFFICIENCY
FOOD CHAIN
Cultivated plant crop 
humans
Cultivated plant crop 
livestockhumans
Intensive grassland
livestockhumans
Grassland and crops
livestockhumans
ENERGY YIELD (kJ x 103
ha-1)
7800 – 11,000
745- 1423
339 (from meat)
3813 (from milk)
1356
Syllabus Objective 3.4

Discuss the concept of biological pyramids.
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Include limitations of the pyramids of
numbers, biomass and energy.
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Ecological pyramids are used as a tool to
illustrate the feeding relationships of the
organisms, which together make up a
community.
PYRAMIDS OF NUMBERS
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The organisms of a habitat are counted and then
grouped into their trophic levels
A progressive decrease in the number of organisms
on each successive level is usually observed.
The bars that make up the pyramid are proportional
to the number of organisms on the trophic levels.
Data is easy to collect
Base may be large or small, depending on organisms
being counted.
PYRAMIDS OF NUMBERS
PROBLEMS WITH PYRAMIDS OF
NUMBERS
1.
Producers vary greatly in size
2.
Sometimes the numbers of organisms on each level
vary so greatly it is difficult to determine a suitable
scale for diagram
3.
The trophic level of an organism may be difficult to
ascertain.
4.
The pyramid may be inverted.
PYRAMIDS OF BIOLOGICAL
MASS
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These pyramids can help overcome some of
the pyramids of numbers
The total biomass of the organisms is
estimated for each trophic level
Typically dry mass is preferred
Base usually largest.
PYRAMIDS OF BIOMASS
PROBLEMS WITH PYRAMIDS OF
BIOMASS

A major problem is that a pyramid of biomass
can be inverted and also it does not take
account of changes over time. The sampling
must all be carried out at one moment in time
and therefore indicates the standing crop and
not the productivity.
PROBLEMS WITH PYRAMIDS OF
BIOMASS

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1.
2.
The biomass at the time of sampling is called the
standing biomass or standing crop biomass (no rates
considered)
This inability to show productivity can be a
problem because:
It does not give an idea of the amount of material
being passed from level to level
If the producers are small, they have a higher
turnover rate than a larger more stable organism.
PYRAMIDS OF NUMBERS AND
BIOMASS
PYRAMIDS OF ENERGY
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1.
2.
3.
4.
5.
The most ideal way of representing organisms on
each trophic level. The advantages are:
Rate of production considered.
Weight for weight, two species may not have the
same energy content
Different ecosystems can be compared
Inverted pyramids are not obtained
Input of solar energy can be added as an extra bar at
the base of the pyramid (sun contribution)
PYRAMID OF ENERGY
PROBLEMS WITH PYRAMIDS OF
ENERGY
1.
2.

Most difficult pyramid for which to obtain
data and require more measurements.
Samples must be combusted and the energy
released is recorded.
Question, how can the data from a pyramid
of biomass be used to obtain a pyramid of
energy?
OVERALL PROBLEMS WITH
ECOLOGICAL PYRAMIDS
1.
2.
3.
Identifying organism’s trophic level
Plant material difficult to measure because a
lot of it is useable only for the plant and not
for subsequent consumers
Dead organic matter (DOM detritivores and
decomposers) are usually left off the
pyramids even though they are very
important.