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ESS – The ecosystem - structure
Syllabus points 2.1.1, 2.1.2, 2.1.3,
2.1.4.
Abiotic
Edaphic
factors
Light
intensity
Number of
predators
Biotic
Topography
Humidity
pH
Age of
population
Light
Temperature
Air
Parasites
Microbial
community
Minerals
Summary
• The living parts of an ecosystem are called
biotic.
• The non-living parts of an ecosystem are
called abiotic.
• Biotic + abiotic = ecosystem
NB the word environment refers to the nonliving part of the ecosystem
Learning objectives
2.1.1 distinguish between biotic and abiotic components
of an ecosystem.
2.1.2 define the term trophic level.
2.1.3 Identify and explain trophic levels in food chains
and food webs selected from the local environment.
2.1.4 explain the principles of pyramids of numbers,
pyramids of biomass and pyramids of productivity, and
construct such pyramids from given data.
Module 2: The Ecosystem
Food Chains
The flow of energy and matter from one organism
to another can be shown using a food chain.
Lets try to draw one for the following organisms:
- stinging nettles
- peacock butterflies (caterpillars)
- blue tits
- sparrow hawks
Terminology
• Now lets try to add the following terminology
– Producer and consumers (1o, 2o, 3o and 4o).
– Herbivore/carnivore/omnivore
– Decomposers
– Trophic levels
Extension:
– Top carnivores
Practice
• Food chains are a very simplified model, but can
be made more realistic by combining them into
food webs.
Produce a food web for an ecosystem of your
choice (ideally local) and then label it with as much
detail as you can.
Extension: what components of systems can you
identify?
Quick check questions
• Are primary consumers always herbivores?
• What is meant by the term trophic level?
• Which trophic level do decomposers feed at?
Ecological Pyramids
Use the blue books to research about pyramids of number,
biomass and productivity.
Areas to focus:
- What does each pyramid show.
- What are the advantages and disadvantages of each
- What are the units for each
- The ‘to do’ task on page 51.
NB This information could be presented in a table.
Extension: complete the ‘to do’ task on page 55.
Questions
1. Why are food chains generally short? (Think
thermodynamics).
a)
b)
How does this support claims for vegetarianism?
What are the implications for the conservation of top carnivores?
2. The amount of energy (KJ/m2/year for each trophic
level is as follows
Plankton (8869)  Copepod (892)  Herring (91)
a)
b)
c)
d)
Sketch a pyramid of productivity.
Calculate the percentage of energy entering the plankton that passes
to the copepod.
Calculate the energy entering the copepod that passes to the
herring.
Calculate the amount of energy entering the food chain per year if
the plankton use 0.1% of the available energy.
Reading
• http://www.bbc.co.uk/news/scienceenvironment-22425219
• Mercury exposure linked to dramatic decline
in Arctic foxes – BBC News
ESS – The ecosystem - structure
Syllabus points 2.1.5, 2.1.6, 2.1.7
Pyramids review
Pyramids are a graphical way of representing data. There are
three types:
- Pyramids of numbers
- The number of individuals at each trophic level.
- Pyramids of biomass
- Biological mass of standing stock at each trophic level at a
particular point in time.
- Pyramids of productivity
- This shows the flow of energy or the rate at which stock is
regenerated.
Each of these representations has advantages and
disadvantages.
Pyramid type
Numbers
(store)
Biomass
(store)
Productivity
(flow)
What it shows
Advantages
Disadvantages
Units
The number of
individuals at each
trophic level
Easy to measure
Doesn’t provide
very useful
information
about feeding
relationships.
None
Biological mass of
standing stock at
each trophic level
at a particular point
in time.
Results in fewer
inverted
pyramids and still
not too difficult
to measure.
Can sometimes
be inverted
because they only
provide a
snapshot in timethey take no
account of
productivity
Grams of
biomass per
metre squared (g
m-2) or in joules
per metre
squared (J m-2).
The the flow of
energy or the rate
at which stock is
regenerated.
Shows the flow of
energy rather than
a ‘snapshot’.
Overcomes the
problem of species
having different
energy content per
unit of mass.
Very hard to
calculate.
Grams per metre
squared per year
(g m-2 yr-1) or
joules per metre
squared per year
(J m-2 yr-1)
Syllabus points
2.1.5 Discuss how the pyramid structure affects
the functioning of an ecosystem.
2.1.6 Define the terms species, population,
habitat, niche, community and ecosystem with
reference to local examples.
2.1.7 Describe and explain population
interactions using examples of named species.
How long can food chains be?
• Discuss with your partner.
– What’s the longest food chain you can think of?
Concentration of toxins
Some toxins do not break down naturally.
Instead they are stored in the tissues of
organisms.
As there are fewer organisms in each successive
trophic level the toxins accumulate.
This problem can be averted by only using
biodegradable toxins.
Vulnerable carnivores
• Read the case study of the snow leopard on
page 18.
• Taking a systems approach what would you do
to help conserve the snow leopard?
– Explain how it would help.
Syllabus points
2.1.5 Discuss how the pyramid structure affects
the functioning of an ecosystem.
2.1.6 Define the terms species, population,
habitat, niche, community and ecosystem with
reference to local examples.
2.1.7 Describe and explain population
interactions using examples of named species.
Definitions
• Species: a group of organisms that interbreed and produce
fertile offspring.
• Niche: where, when and how an organism lives. No two
different species can have the same niche because a niche
completely defines the species.
• Population: a group of organisms of the same species living
in the same area at the same time, and which are capable
of interbreeding.
• Community: a group of organisms living and interacting
with each other in a common habitat.
• Habitat: the environment in which a species usually lives.
• Ecosystem: a community of interdependent organisms and
the physical environment they inhabit.
Syllabus points
2.1.5 Discuss how the pyramid structure affects
the functioning of an ecosystem.
2.1.6 Define the terms species, population,
habitat, niche, community and ecosystem with
reference to local examples.
2.1.7 Describe and explain population
interactions using examples of named species.
Species B
Species
Interactions
Negative
Positive
Mutualism
Parasitism
Negative
Predation
Competition
Species A
Positive
Species B
Species
Interactions
Positive
Mutualism
Species A
Positive
A symbiotic relationship in
which both species
benefit.
Negative
Parasitism
One organism benefits at
the expense of the other.
Ectoparasites and
endoparasites.
Competition
Predation
Negative
When one animal hunts
and eats another.
This occurs when
resources are limited.
Intraspecific and
interspecific.
Activities
1. Research an example of each of the four
species interactions. (Mutualism, parasitism,
predation and competition).
2. What is meant by a symbiotic relationship?
Extension: are there any other types of
interaction that could be possible?
Discuss in pairs
1. What is the difference between predators
and scavengers?
2. Do parasites kill their hosts?
3. Are these types of relationships ‘fixed’ over
evolutionary time?
4. What is the relationship between an
elephant and plants it tramples on?
5. How would we classify what happens if a lion
kills a hyena but doesn’t eat it?
Syllabus points
2.1.5 Discuss how the pyramid structure affects
the functioning of an ecosystem.
2.1.6 Define the terms species, population,
habitat, niche, community and ecosystem with
reference to local examples.
2.1.7 Describe and explain population
interactions using examples of named species.

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