Unit 1
Communication, Homeostasis and Energy
Module 3: Ecosystems and Sustainability
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Explain the significance of limiting
factors in determining the final size of
a population.
Explain the meaning of the term
carrying capacity.

A group of organisms of the same
species, which live in the same place,
at the same time and can interbreed
with one another.

Sigmoid growth curves
 Populations tend to increase until
reaching the maximum number that can
live in that habitat.

Limiting factor
 Factor which stops a population from
increasing in size.
 In wild populations, different factors may
effect population growth at different times
and in different ways

Suggest the limiting
factors for a
population of song
thrushes in the gardens
of a small town.
 Limited supply of
slugs, snails and
invertebrates (food)
 Nesting sites
 Predators
 parasites

Limiting factors also
include the abiotic
factors
 Water
 Light
 Oxygen
 Shelter
 temperature

Abiotic - Non living
factors

Biotic – living
factors
 Temperature
 Competition
 Light intensity
 Predation
 Soil pH
 disease
 Availability of water
 Availability of
minerals

Density dependent
factors
 Effect increases as
population density
increases
 Population level off,
then decrease
 Example - availability
of food

Density
independent
factors
 Effect independent
of the size of the
population
 Example – forest fire

The maximum population size that can
be maintained by an area over a
period of time.
In the wild it is
unlikely that a
population will
enter a decline
or death phase
 A population
will fluctuate up
and down
about the
carrying
capacity
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Describe predator–prey relationships
and their possible effects on the
population sizes of both the predator
and the prey.

Patterns of predator prey interaction
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Stable coexistence
Cyclical variations
Erratic swings
Extinction of prey species
Important factors to consider

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Carrying capacity of the habitat
Reproduction rate of prey
Reproduction rate of predator
Degree of flexibility of predator to switch prey

Evidence suggests that
 The size of the predator population is influenced
by the size of the prey population
 And vice versa
Predatory mite and its prey were introduced
to a controlled environment
 The populations of both mites oscillate

 The population of the prey rises followed by the
population of the predator
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Rise in population of predator follows that of the
prey
Prey population limited by the rise in predators
Reduction in food supply limits the predator
population
Prey population begins to increase again
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In the wild, it is more likely that the
predator will have more than one
food source.
Although predatory-prey interactions
are thought to be one of the main
factors affecting the populations of
lynxes and snowshoe hares in Northern
Canada.
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Convert the information in the table
into a graph to illustrate any patterns
that may exist.
Label and number the axes clearly
Decide how to represent the
populations of hare and lynx on the
same graph.
year
Population of hare
(thousands)
Population of Lynx
(thousands)
1845
12
22
1850
10
39
1855
63
6
1860
72
21
1865
139
3
1870
3
60
1875
62
4
1880
83
35
1885
120
63
1890
12
10
1895
70
40
1900
10
5
1905
68
43
1910
20
2
Describe and explain the patterns shown by the graph
By removing prey who are strong
competitors, weaker competitors can
survive
 Reduce effect of competitive exclusion
 The ecosystem benefits from

 Increasing species diversity
 Increasing stability
 The ability to adapt to environmental change

Examples where removing predators has
collapsed an ecosystem
 Otters and the sea kelp forests

Predator-prey populations
 Look at the two graphs on the worksheet
 Answer the accompanying questions

Predatory mite vs Prey
1. Predator is the secondary consumer,
prey mite is the primary consumer
2. Energy lost as transferred through trophic
levels
▪
▪
Less energy to support 2o consumers
As biomass of each individual is the same, the
number of secondary consumers will be
smaller than the number of primary consumers
Lynx vs. Snowshoe hare

Lynx furs oscillated in 7-8 year cycles, never
rising above 6000 furs trapped, but in some
years almost none were trapped
Lynx and hare populations oscillate on the
same time scale
1.
2.
Which fits the predator prey theory as lynx data
shadows that of the snow shoe hare after about 2
years.
Other factors
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Parasites
Inconsistent trapping
No records of other possible factors
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Explain, with examples, the terms
interspecific and intraspecific
competition.
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Interspecific interactions
 Between individuals of different species
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Intraspecific interactions
 Between individuals of the same species

Which type of interaction is more
intense, interspecific or intraspecific?
Why?
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Individuals that are best adapted will
survive to reproduce
Slows down population growth and
population enters stationary phase
Keeps population stable
 Decrease in population size, competition
reduces, population size increase
 Vice versa
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intense
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Occurs when two niches overlap
Affects population size and distribution
of a species in an ecosystem

The sum of
 An organism’s adaptations
 The resources it needs
 The lifestyle to which it is fitted

Paramecium
aurelia and P.
caudatum
Experiments

When cultured together Paramecium aurelia
has a competitive advantage over P.
caudatum for gaining food.

The more overlap between two
species’ niches would result in more
intense competition
 Competitive exclusion principle

When grown together, there was
competition for food with P. aurelia
obtaining food more effectively than
P. caudatum, which died out.

Changes in
population size of
two species of flour
beetle, Tribolium
confusum and
Tribolium
castaneum,
competing for food
and space in a
container of
wholemeal flour.

Several factors work
together to
influence
population size and
distribution
 Example –
distribution of two
species of barnacle.

Chthamalus
stellatus
 Dessication at the
top of its range
 Better at coping
with temperature
fluctuations and
exposure to dry
air.
 Competition with
Balanus at the
bottom of its
range.

Balanus balanoides
 Dessication and
competition with
Chthamalus at the top of
its range
 Faster growing, so wins the
competition for limited
space on the rocks in the
middle of its range
 Predation by Nucellus at
the bottom of its range
and competition with
seaweed for space.

Competition
 How much can you remember?
 Complete the worksheet, commenting on
interspecific competition and interacting
factors
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Past paper exam questions
 Competition
▪ 2804 Jan 05 question 4
 Populations and competition
▪ 2804 Jun 06 question 4
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Distinguish between the terms
conservation and preservation.
Discuss the economic, social and
ethical reasons for conservation of
biological resources.

Biodiversity
 The range of habitats, communities and species
that are present in an area, and the genetic
variation that exists within each species.

Conservation
 Active management of habitats in order to
maintain or increase biodiversity
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Preservation
 Protects species or habitats e.g. by creating a
nature reserve

Management of human use of the
biosphere so that it may yield the
greatest sustainable benefit to present
generations while maintaining it’s
potential to meet the needs and
aspirations of future generations.
 World conservation strategy
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Ecosystems are not static, they are
dynamic i.e. they change over time
Preserving an area without active
management, may not be the best
thing for that area.
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Conservation is the protection of
ecosystems, habitats and species
These means taking action to halt
destruction and extinction
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Conservation involves
 Managing areas of land
 Taking steps to encourage new habitats
 Removing animals to captivity
 Growing plants in cultivation
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The main reasons given for conserving
species are
 Economic
 Ethical
 social
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Natural ecosystems provide services
 Examples
▪ Regulation of atmosphere and climate
▪ Formation and fertilisation of soil
▪ Recycling of nutrients
▪ Growth of timber, food and fuel
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Ecosystems also provide goods such
as wood and fish for free.
Tourism
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Species become extinct as a result of
human action
Humans have a responsibility to
maintain species, ecosystems and
habitats for future generations
All organisms have a right to survive
and live in the way to which they have
become adapted.

People enjoy
 visiting wild places
 Observing wildlife
▪ The large animals are sustained by an
interdependent web which includes a huge
number of species

Wellbeing – physical, intellectual and
emotional health

Explain how the management of an
ecosystem can provide resources in a
sustainable way, with reference to
timber production in a temperate
country.


Removing timber from a forest or
woodland in a manner that allows
similar amounts to be removed year
after year.
Maintaining the forest ecosystem
 Allowing all the different habitats and
species to survive
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When a deciduous tree is cut it
regrows from its base
The new growth consists of several
stems
 Rotational coppicing
 Coppice with standards

Clear felling can
 destroy habitats
 Reduce soil mineral levels
 Increase soil erosion
 Increase flooding

Increasing biodiversity
 Leave each section of woodland for 50-
100 years
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Selective felling where only the largest
most valuable trees are felled.
Any tree harvested is replaced by
another
Local people benefit from the forest.
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Matching tree species to climate,
topography and soil type
Planting trees the best distance apart.
Controlling pests and pathogens
Using every part of each tree felled
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Maintaining a sustainable forest ecosystem
 Gather information on biodiversity and wildlife
 Consider transport links and markets
 Formulate ecological and business plans
 Select appropriate species to grow
 Measurement of forest growth and structure
 Application of ecologically sensitive systems
▪ Clear felling vs. selective felling vs. strip felling
 Recreational use of forests by the public
 Use of broad-leaved deciduous species
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Explain that conservation is a dynamic
process involving management and
reclamation.

Ecosystems are dynamic and everchanging
 Heathland if abandoned would gradually revert
to woodland again (natural climax community)
with the loss of important species

Conservation is an on-going process, its
demands change as the ecosystem itself
changes.
 This requires constant monitoring of the habitat
and biodiversity.
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Management strategies include:
 Raising carrying capacity
 Encourage dispersion of individuals e.g.
wildlife corridors
 Control predators
 Vaccinate against disease
 Preserve habitats
▪ Prevent pollution
▪ Intervene to restrict succession
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Designated as a Site of Special
Scientific Interest
“key species” were identified for
consideration when management
plans for conservation areas are
drawn up
Threats identified
 Disturbance to animals caused by humans
 Pollution leading to nutrient enrichment
 Drop in groundwater levels
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To maintain and increase biodiversity
To restore and reclaim former
heathland
 Maintain a high water table
 Allow cattle to graze
 Removal of trees

Outline, with examples, the effects of
human activities on the animal and
plant populations in the Galapagos
Islands

Small group of
Islands lying on
the equator to
the west of
Ecuador
There are
about 24
Islands
 All islands are
the tips of
volcanoes
that erupted
under the sea
millions of
years ago
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The unique ecosystems, communities
and endemic species are under threat
 Population growth
 Over-fishing e.g. sea cucumber
 Tourism
 Exotic species
▪ Feral dogs eat tortoise eggs
▪ Cats hunt lava lizard and young iguanas
▪ goats
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Quarantine system
 All boats and tourists that arrive are
searched for exotic species
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
Use natural predators to control pest
populations
Culling
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Isabella had a huge feral goat population
Plan
 To destroy the entire goat population
▪ “Judas Goats” were released with radio collars
▪ Specially trained hunters with high-performance
weapons used information from aerial surveys and GPS.
▪ Goats were dispatched humanely

Success Story
 By 2006 all goats had been destroyed
 Increases in growth of tree ferns and vegetation
 Tortoise population now expected to thrive

36% of coastal areas are designated
as “no-take” areas
 No extraction of resources
 Communities are left undisturbed

On the Island, Espanola, there were
only 14 giant tortoises left
 These were all captured and kept for
captive breeding
 Over 100 offspring have now been
returned to the Island
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Finding a balance between environmental,
economic and social concerns are essential for
conservation to be successful
“Lonesome George”
The last remaining Pinta Tortoise