E.F. ACADEMY
I.B. Biology Core
Topic 4: Ecology
Jon Whitlow
9/9/2014
Topic 4: Ecology
4.1 Species, communities and ecosystems
p2 - 16
4.2 Energy flow
p17 - 26
4.3 Carbon cycling
p27 - 30
4.4 Climate change
p31 - 39
1
Ecology
4.1 Species, communities and ecosystems
•
Species are groups of organisms that can potentially interbreed to produce
fertile offspring.
Species: a group of organisms that can interbreed and produce fertile offspring.
Provided, of course, they are in the same area at the same time. Organisms of the
same species which are separated from others are said to be reproductively
isolated. This isolation may be either physical or behavioural.
Physical separation may lead to formation of sub-species.
Horse
Donkey
Mule
2
Greenfinch
Canary
Mule- a sterile offspring
Q1. The term species is defined as a potentially interbreeding population
having a common gene pool and producing fertile young. Outline why
this definition cannot be applied to all living organisms.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(Total 4 marks)
3
Habitat: the environment in which a species normally lives or the location of a
living organism.
Population: a group of organisms of the same species who live in the same area at
the same time.
A community is formed by populations of different species living together
and interacting with each other. A community forms an ecosystem by its
interactions with the abiotic environment.
Ecosystem: a community reacting together and with the non-living (abiotic)
environment.
Ecology: the study of relationships between living organisms and between
organisms and their environment.
Members of a species may be reproductively isolated in separate populations.

New
species
arise
when
one
existing
species
splits
into
two
reproductively isolated populations that go their separate ways.

This most commonly happens when the two populations become
physically separated from each other (allopatric speciation)

e.g. The genome map suggests that about 2 million years ago,
individuals of a single ape species were divided by the Congo River.

The populations must be reproductively isolated, so that they could
not interbreed and there was no gene flow between the groups.

As the environmental conditions were different on either side of the
river they started evolving separately.
4

The allele frequencies in the two populations became different. They
became separate species — chimpanzees and bonobos — about 1
million years ago.

Bonobos have a genome which is 99.6 percent identical to the
chimpanzee genome and 98.7 percent identical to the human genome
— basically they are just as related to humans as chimpanzees.
Chimpanzee
Bonobo
伀Species have either an autotrophic or heterotrophic method of nutrition (a few
5
Species have either an autotrophic or heterotrophic method of nutrition (a few
species have both methods).
Autotrophs are organisms that synthesize their organic molecules from
simple inorganic substances whereas heterotrophs are organisms that obtain
organic molecules from other organisms.
Autotrophs obtain
inorganic
nutrients from the
abiotic environment.
Autotrophs are organisms that synthesize their organic molecules from
simple inorganic substances whereas heterotrophs are organisms that obtain
organic molecules from other organisms.
Photoautotrophic organisms use light as an energy source which enables
them to synthesise their own organic molecules (photosynthesis).
Chemoautotrophs use the energy from reduced compounds, which they
oxidise, to enable then to synthesise organic materials
e.g. NH4+ -> No3- + 3H
H2 + CO2 -> CH2O + O2 (not balanced)
6
Consumers are heterotrophs that feed on living organisms by ingestion. They are
organisms that ingest other organic matter that is living or recently killed.
Detritivores are heterotrophs that obtain organic nutrients from detritus by
internal digestion. i.e. an organism that ingests non-living organic matter. A
decomposer
Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms
by external digestion. They are organisms that live on or in dead organic
matter, secreting digestive enzymes into it and absorbing the products of
digestion.
7
Q2
What term refers to a community and its abiotic environment?
A.
Biosphere
B.
Ecosystem
C.
Habitat
D.
Niche
Q3
What is a community?
A. A group of organisms living and interacting in the same trophic level
B. A group of populations living and interacting in a food chain
C. A group of organisms of the same species living and interacting in an
ecosystem
D. A group of populations living and interacting in an area
Q4
Which group of organisms in the carbon cycle converts carbon into a
form that is available to primary consumers?
A. Decomposers
B. Detritus feeders
C. Producers
D. Secondary consumers
8
Q5
Q6
What are the two components of an ecosystem?
A.
Community and abiotic environment
B.
Species and habitat
C.
Habitat and abiotic environment
D.
Species and community
Which organisms externally digest dead organic matter and then absorb
the nutrients?
Q7
A.
Autotrophs
B.
Detritivores
C.
Heterotrophs
D.
Saprotrophs
What are the two components of an ecosystem?
A.
Species and community
B.
Habitat and abiotic environment
C.
Community and abiotic environment
D.
Species and habitat
9
Q8
What term refers to a community and its abiotic environment?
A.
Biosphere
B.
Ecosystem
C.
Habitat
D.
Niche
Q9.
Which of the following terms describe(s) species X?
I.
Heterotroph
II.
Primary consumer
III.
Secondary consumer
A.
I and II only
B.
I and III only
C.
II only
D.
I, II, and III
10
Ecosystems have the potential to be sustainable over long periods of time

Many different factors interact to determine population size, and it can be
very difficult to determine which factors are the most important.

These factors can be split into two broad groups:
1. Abiotic
Factors:
Non-living
components
of
the
environment;
e.g.
Temperature, Humidity, pH, altitude. These factors tend to control a
population in a density independent manner.
2. Biotic Factors: Living components of the environment, as all living things
compete, these factors tend to be density dependent. e.g. competition for
mates, territories, are forms of competition within a species i.e. intra specific
competition.
An organism’s niche refers to the biotic and abiotic factors that the organism
needs in its habitat.
Q10. (i)
Define the term niche.
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Explain the niche concept using a named organism.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(4)
(Total 8 marks)
11
Intraspecific Competition

Intraspecific competition is competition for resources between
members of the same species.

This is more significant than interspecific competition, since member
of the same species have the same niche and so compete for exactly
the same resources.

Intraspecific competition tends to have a stabilising influence on
population size because it is density dependent.

If the population gets too big, intraspecific population increases, so the
population falls again.

If the population gets too small, intraspecific population decreases, so
the population increases again:
InterSpecific Competition
Factors such as predation and disease involve inter specific competition

The populations of predators and their prey depend on each other, so
they tend to show cyclical changes.

If the population of the prey increases, the predator will have more
food, so its population will start to increase.

This means that more prey will be eaten, so its population will
decrease, so causing a cycle in both populations:
Pink =Predator: Blue= Prey
12
The competitive exclusion principle:

Two species cannot coexist in the same habitat if they have the same
niche.

They will compete, and one species will win the competition.

This principle also works in reverse: if two species are observed to
compete then they must have the same niche.
e.g. Acorn Barnacles Balanus and Chthamalus compete for the most favourable site,
near the sea, on rocky shores;
Balanus
Chthalamus
Balanus outcompetes Chthalamus (it grows faster and prises Chthalamus off the
rock) and so it occupies the most favourable site on the rock – nearest the sea.
Grey Squirrels outcompete Red Squirrels. They are bigger, more active (Reds
hibernate) and carry diseases to which they are immune but which kill Reds.
13
Red Squirrel (nice, nice, nice)
Grey Squirrel (evil, evil, evil)

Species with narrow niches are called specialists.

Many different specialists can coexist in the same habitat because they
are not competing, so this can lead to high diversity.

For example warblers in a coniferous forest feed on insects found at
different heights. By feeding at different heights in the same tree they
avoid competition and can co-exist
14

Specialists rely on a constant supply of their food, so are generally
found in abundant, stable habitats such as the tropics
Competition between species leads to succession.
e.g.

Different species of plants naturally colonise a habitat in a predictable
order, until finally a stable community is reached, called the climax
community.

Each plant species in turn changes its environment (e.g. by creating
deeper soil, or providing shade), making the environment more
suitable for new species to colonise.

These
new
species
are
usually
bigger
plants
with
a
larger
photosynthetic area, so they outcompete and replace the older species.
So each plant effectively causes its own demise.

The plants colonising early in succession (the pioneer species) tend to
be small and fast growing, with shallow roots and wind-dispersed
seeds.

The plants colonising late in succession tend to be tall and slow
growing, with deep roots and animal-dispersed seeds.

The successive stages are called seral stages, or seral communities, and
the whole succession is called a sere.
15

It will usually take a few hundred years to reach a stable climax
community.

The
climax
community
is
usually
a
forest,
though
this
varies
depending on the climate and the underlying rock. (abiotic factors)
16
4.2 Energy flow

Most ecosystems rely on a supply of energy from sunlight.

Light energy is converted to chemical energy in carbon compounds by
photosynthesis.

Chemical energy in carbon compounds flows through food chains by means
of feeding.

Plants are PRODUCERS and everything else consumes they energy that they
produce making them CONSUMERS.


Food chains and webs are separated out into TROPHIC LEVELS.
Energy released from carbon compounds by respiration is used in living
organisms and converted to heat. Heat is waste energy.

Living organisms cannot convert heat to other forms of energy.

Heat is lost from ecosystems.

Energy losses between trophic (energy) levels restrict the length of food
chains and the biomass of higher trophic levels
17
A simple food chain

The energy found at each level can be represented by a Pyramid of
Energy.

The loss of energy at each level is due to heat lost by respiration and
by indigestible material

Usually a maximum of 10% is passed from one trophic level to
another.

Decomposers are placed on the primary consumer level even though
they take their nutrition from several trophic levels
.
18

Most (all?) consumers feed on more than one type of food. This means
that a simple food chain does not represent that which is actually
happening.

Links between food chains form food webs.
A simple food web:
Note:
In the food chain: Grass > Grasshopper > Shrew > Hawk
The Hawk is a tertiary consumer.
In the food chain: Grass > Grasshopper > Shrew > Snake > Hawk
The Hawk is a quaternary consumer; it is feeding at more than one level in
the food web.
19
In this representation of a food web.
Find;
1. A food chain where the Hawk is feeding as a Secondary consumer
2. A food chain where the Hawk is feeding as a Tertiary consumer
3. A food chain where the Hawk is feeding as a Quaternary consumer
4. Find food chains in which the mouse is feeding at three different levels
5. Why, in energy terms, is it beneficial to have as few links as possible in
the food chain?
20
Q11
The total solar energy received by a grassland is 5 × l05 kJ m–2 y–1. The net production
of the grassland is 5 × 102 kJ m–2 y–1 and its gross production is 6 × l02 kJ m–2 y–1. The total
energy passed on to primary consumers is 60 kJ m–2 y–1. Only 10% of this energy is passed
on to the secondary consumers.
(a)
Calculate the energy lost by plant respiration.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(b)
Construct a pyramid of energy for this grassland.
(3)
(Total 5 marks)
21
Q12. The diagram below is a simplified version of a food web from
Chesapeake Bay. The arrows indicate the direction of energy flow and
the numbers indicate species within the food web.
At which trophic level or levels does species II function?
A.
2nd and 3rd consumer
B.
3rd consumer
C.
3rd and 4th consumer
D.
Producer
22
Q13.
If 2 000 000 kJ m–2 yr–1 is available from producers in an
ecosystem, how much energy (in kJ m–2 yr–1) is usually available to the
tertiary consumers?
A. 200 000
B. 20 000
C. 2000
D. 200

Other types of pyramid can be drawn:
1. Pyramids of numbers; these show each living organism as a specific
area in the pyramid. So a large oak tree weighing several tons
would be given the same space as a single aphid. Frequently these
pyramids were inverted.
2. Pyramids of Biomass; These show the amount of living material present
at a particular time, no account is taken of the rate at which a
particular organism or population grows, so in an aquatic ecosystem
where the plants (phytoplankton) reproduce very quickly even though
there are few at any one time:
23
Pyramids of energy take into account this rate of increase by taking the energy
per unit area (m2) per unit time (year)
Q14.
What are the units of a pyramid of energy?
A. kJ m-2 yr-1
B. kJ m-1 yr-1
C. J m-3 s-1
D. J m2 s-1
24
Q15.
The diagram shows organisms in a food web.
(a)
(i)
Name all the secondary consumers in this food web.
...............................................................................................................
...............................................................................................................
(1)
(ii)
Use the diagram to explain the likely effect of a sudden decrease in the
stickleback population on the population of mayfly larvae.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
(2)
25
(b)
A pyramid of energy for this food web is shown below. The bars are drawn to
the same scale.
(i)
Use the pyramid of energy to calculate the percentage efficiency of
energy transfer between producers and primary consumers. Show your
working.
efficiency = .......................................... %
(2)
(ii)
The average efficiency of energy transfer between producers and
primary consumers in pyramids of energy is around 10 %.
Suggest why the efficiency of energy transfer from producers to primary
consumers
in this food web is higher than 10 %.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
(2)
(c)
Energy from the sun may ultimately end up in dead plant matter. Describe
how.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(Total 9 marks)
26
The supply of inorganic nutrients is maintained by nutrient cycling
4.3 Carbon cycling
•
Autotrophs convert carbon dioxide into carbohydrates and other carbon
compounds.

CO2 in air and water > organic compounds in Producers via Photosynthesis.
27
Q16. Which group of organisms in the carbon cycle converts carbon into a
form that is available
•
to primary consumers?
A.
Decomposers
B.
Detritus feeders
C.
Producers
D.
Secondary consumers
In aquatic ecosystems carbon is present as dissolved carbon dioxide and
hydrogen carbonate ions.
•
Carbon dioxide diffuses from the atmosphere or water into autotrophs.
•
Carbon dioxide is produced by respiration and diffuses out of organisms into
water or the atmosphere. C6H12O6 > 6CO2 + 6H20
•
Methane is produced from organic matter in anaerobic conditions by
Methanogenic Archaean’s (bacteria) and some diffuses into the atmosphere or
accumulates in the ground.
28
•
Methane is oxidized to carbon dioxide and water in the atmosphere. The
CO2 re-joins the Carbon cycle
•
Peat forms when organic matter is not fully decomposed, because of acidic
and/or anaerobic conditions in waterlogged soils and therefore acts as a major
source of methane.
•
Partially decomposed organic matter from past geological eras was
converted either into coal or into oil and gas that accumulate in porous rocks.
These materials act as Carbon Sinks.
•
Carbon dioxide is produced by the combustion of biomass and fossilized
organic matter.
•
Animals such as reef-building corals and Mollusca have hard parts that are
composed of calcium carbonate and can become fossilized in limestone. The
limestone also acts as a store of CO2 – a carbon sink.
Q17.
Clearing forests and burning the vegetation affects the carbon dioxide
concentration in the atmosphere.
Describe how and explain why.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(4)
29
(c)
During photosynthesis, oil-palm trees convert carbon dioxide into organic
substances. Describe how.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(6)
30
4.4
Climate change

Carbon dioxide and water vapour are the most significant greenhouse gases.

The earths mean average temperature is regulated by a steady
equilibrium which exists between the energy reaching the earth from
the sun and the energy reflected by the earth back into space.

The incoming radiation is short wave ultraviolet and visible radiation.

Some of the radiation will be absorbed by the atmosphere and some
of it will be reflected back from the earth’s surface into space.

The radiation that is reflected back into space is infrared radiation
which has a longer wavelength.

Greenhouse gases such as carbon dioxide, methane, and oxides of
nitrogen tend to absorb some of the reflected infrared radiation and
re-reflect it back towards the earth.

This is what causes the greenhouse effect and it results in an increase
in average mean temperature on earth.
31

It is a natural phenomenon. However, since there has been an increase
in the greenhouse gases in the past century, this has resulted in an
increase of the greenhouse effect leading to higher than normal
average temperatures which could lead to disastrous consequences in
the future.
32
Q18. Which of the following gases will contribute to the greenhouse effect?
I. Oxygen
II. Nitrous oxide
III. Argon
A. I only
B. II only
C. I and II only
D. I, II and III
Q19. Which human activities may increase or decrease the greenhouse effect?
Increases greenhouse effect
Decreases greenhouse effect
A.
Deforestation
More use of fossil fuels
B.
Reforestation
More use of solar power
C.
Less use of air conditioning
Less use of public transport
D
More cattle farming
Reforestation
33
Summary:
1. The incoming radiation from the sun is short wave ultraviolet and visible
radiation.
2. Some of this radiation is absorbed by the earth’s atmosphere.
3. Some of the radiation is reflected back into space by the earth’s surface.
4. The radiation which is reflected back into space is infrared radiation and
has a longer wavelength.
5. The greenhouse gases such as CO2, in the atmosphere, absorb some of this
infrared radiation and re-reflect it back towards the earth. The more
CO2 in the atmosphere the greater this effect.
6. This causes the greenhouse effect and results in an increase in average
mean temperatures on earth.
7. A rise in greenhouse gases results in an increase of the greenhouse effect
which can be disastrous for the planet.
34
Q20. The graph below shows the variation in the concentration of atmospheric carbon dioxide
since 1970.
375
370
365
360
355
CO 2
concentration
/ ppm
350
345
340
335
330
325
2000
1995
1990
1985
1980
1975
1970
320
[Source: C D Keeling and T P Whorf, Atmosphere CO2 concentrations (ppm) derived from in situ air
samples, collected at Mauna Loa Observatory, Hawaii]
The annual fluctuation is mainly the result of changes in the levels of photosynthesis
associated with the seasons in Northern Hemisphere forests.
35
(a)
(i)
Describe the overall trend shown in the graph.
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Suggest a cause for the overall trend throughout the period 1970–1999.
...........................................................................................................................
...........................................................................................................................
(1)
(b)
(i)
Using a clear label, identify any one point on the graph which shows the CO2
level in mid-summer.
(1)
(ii)
Explain why the concentration of CO2 varies with the seasons.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(c)
Identify one gas, other than CO2 , which is contributing to the enhanced greenhouse
effect.
.....................................................................................................................................
(1)
(Total 6 marks)
•
Other gases including methane and nitrogen oxides have less impact.
•
The impact of a gas depends on its ability to absorb long wave radiation as
well as on its concentration in the atmosphere.
36
•
The warmed Earth emits longer wavelength radiation (heat).
•
Longer wave radiation is absorbed by greenhouse gases that retain the heat
in the atmosphere.
•
Global temperatures and climate patterns are influenced by concentrations
of greenhouse gases.
•
There is a correlation between rising atmospheric concentrations of carbon
dioxide since the start of the industrial revolution 200 years ago and average
global temperatures.
•
Recent increases in atmospheric carbon dioxide are largely due to increases
in the combustion of fossilized organic matter.
37
Global warming could have a number of disastrous consequences largely
affecting the arctic ecosystems:

The arctic ice cap may disappear as glaciers start to melt and break up
into icebergs.

Permafrost will melt during the summer season which will increase the
rate of decomposition of trapped organic matter, including peat and
detritus. This in turn will increase the release of carbon dioxide which will
increase the greenhouse effect even further.

Species adapted to temperature conditions will migrate north which will
alter food chains and have consequences on the animals in the higher
trophic levels.
38

Marine species in the arctic water may become extinct as these are very
sensitive to temperature changes within the sea water.

Polar bears may face extinction as they lose their ice habitat and
therefore can no longer feed or breed as they normally would.

Pests and diseases may become quite common with rises in temperature.

As the ice melts, sea levels will rise and flood low lying areas of land.

Extreme weather events such as storms might become common and have
disastrous effects on certain species.

39
Answers;
Q1
subspecies may be isolated in niches / minor differences in gene pool /
potentially able to interbreed but do not;
some species reproduce asexually / parthenogenesis;
interspecific hybridization / artificial methods / IVF technology;
species definition cannot be applied to bacteria;
species still evolve / cannot be applied to fossils;
difficult to know if geographically separated populations can interbreed;
some individuals are infertile;
Q2
B
Q3
D
Q4
A
Q5
A
Q6
D
Q7
C
Q8
B
Q9
D
40
Q10 (i)
the habitat of an organism, its nutrition / feeding habits and interactions /
relationships with other organisms / other organisms / the role of an organism
in a habitat / ecosystem
1
(ii) localization of named animal in its habitat;
description of spatial habitat;
description of feeding habitat: type of food;
time of day;
interactions with other organisms: prey;
predators;
competition;
reproductive strategies;
breeding sites;
Q11 (a)
plant respiration = gross production – net production /
6 × 102 kJ m–2 y –1 – 5 × 102 kJ m –2 y –1;
= 1 × 102 / 100 kJ m–2 y –1;
2
41
(b)
6 kJ m–2 y –1
60 kJ m–2 y –1
600 kJ m –2 y –1
correct pyramid shape;
6 kJ m–2 y–1
producer and primary consumer values correctly inserted;
3 max
[5]
Q12
A
Q13
C
Q14
A
Q15(a)
(i)
Stickleback + caddis fly (larva) + stonefly (larva);
1
(ii)
1.
(With fewer fish) reduced predation / not being eaten results in
more freshwater shrimps;
2.
Increased competition for food/resources / more producers
eaten by shrimps / more shrimps eating producer
3.
Less food/resources for mayfly;
2 max
(b)
(i)
1.
Two marks for correct answer in range 16.8 to 18.9;
Ignore additional decimal places.
2.
One mark for incorrect answer in which candidate divides 19 to 21
by 111 to 113;
2
42
(ii)
1.
Single-celled producers are more digestible / contain less cellulose
(than plants) / less energy lost in faeces;
2.
All of producer eaten/parts of plant not eaten;
3.
Less heat/energy lost / less respiration;
2 max
(c)
1.
Photosynthesis/light dependent reaction/light independent reaction;
2.
Carbon-containing substances;
2
[9]
Q16
Q17
C
1. Carbon dioxide concentration increases;
Clearing
2. No/Less vegetation so no/less photosynthesis / photosynthetic organisms;
3. No/Less carbon dioxide removed (from the atmosphere);
Burning
4. Burning/combustion releases / produces carbon dioxide;
4
(b)
1. Carbon dioxide combines with ribulose bisphosphate/RuBP;
2. Produces two molecules of glycerate (3-)phosphate/GP;
3. Reduced to triose phosphate/TP;
4. Using reduced NADP;
5. Using energy from ATP;
6. Triose phosphate converted to other organic substances/ named
organic substances/ribulose bisphosphate;
43
7. In light independent reaction/Calvin cycle;
6 max
Q18
C
Q19
D
Q20 (a)
(b)
(c)
(i)
with time, the atmospheric concentration of CO2 has increased;
(ii)
the increased use of fossil fuels / more automobiles;
increased deforestation;
Do not accept greenhouse effect.
1
1 max
(i)
any trough, clearly labelled at the bottom;
(ii)
CO2 is a raw material for photosynthesis;
there is an increase in the rate of photosynthesis in the summer;
therefore less CO2 in the air during the summer as it is being used for
photosynthesis;
increase in CO2 in winter because less photosynthesis due to trees
losing leaves in autumn-winter / lower temperatures / shorter days
with less light;
2 max
CFCs / CH4 / N2O;
Names are acceptable eg methane, nitrous oxide. Do not accept SO2.
1
1
[6]
44