Essential idea: The continued survival of living organisms
including humans depends on sustainable communities.
By Chris Paine
https://bioknowledgy.weebly.com/
Honey bees are in decline in many parts of the world,
the phenomena is known as Colony Collapse Disorder
(CCD). Though many factors, including parasites are
involved it is likely that a major factor is in CCD is
modern farming practices, particularly pesticide use.
This is ironic given that approximately a third of all
crops rely on bees for pollination. Food production is
reliant on healthy, sustainable communities of animals
surrounding the agricultural land.
4.1 Species, communities and ecosystems
http://www.gaiahealthblog.com/wordpress1/wp-
content/uploads/2013/11/bee-and-daisy.jpg

Understandings
Statement Guidance
4.1.U1 Species are groups of organisms that can potentially
interbreed to produce fertile offspring.
4.1.U2 Members of a species may be reproductively isolated in
separate populations.
4.1.U3 Species have either an autotrophic or heterotrophic method
of nutrition (a few species have both methods).
4.1.U4 Consumers are heterotrophs that feed on living organisms by
ingestion.
4.1.U5 Detritivores are heterotrophs that obtain organic nutrients
from detritus by internal digestion.
4.1.U6 Saprotrophs are heterotrophs that obtain organic nutrients
from dead organisms by external digestion.
4.1.U7 A community is formed by populations of different species
living together and interacting with each other.
4.1.U8 A community forms an ecosystem by its interactions with the
abiotic environment.
4.1.U9 Autotrophs obtain inorganic nutrients from the abiotic
environment.
4.1.U10 The supply of inorganic nutrients is maintained by nutrient
cycling.
4.1.U11 Ecosystems have the potential to be sustainable over long
periods of time.

Applications and Skills
Statement Guidance
4.1.S1 Classifying species as autotrophs, consumers,
detritivores or saprotrophs from a knowledge of their
mode of nutrition.
4.1.S2 Setting up sealed mesocosms to try to establish
sustainability. (Practical 5)
Mesocosms can be set up in open tanks, but
sealed glass vessels are preferable because entry
and exit of matter can be prevented but light can
enter and heat can leave. Aquatic systems are
likely to be more successful than terrestrial ones.
4.1.S3 Testing for association between two species using
the chi-squared test with data obtained by quadrat
sampling.
To obtain data for the chi-squared test, an
ecosystem should be chosen in which one or
more factors affecting the distribution of the
chosen species varies. Sampling should be based
on random numbers. In each quadrat the
presence or absence of the chosen species
should be recorded.
4.1.S4 Recognizing and interpreting statistical significance.

http://www.slideshare.net/gurustip/communities-and-ecosystems

4.1.U1 Species are groups of organisms that can potentially interbreed to produce fertile offspring.
Species is a group of organisms that can interbreed to produce fertile offspring
If species are not closely related it is often impossible
for individuals of the different species to breed.
If members of two closely related species do interbreed and
produce offspring the hybrids will be sterile e.g. mules.
https://i.ytimg.com/vi/8P01Y6LDwi0/maxresdefault.jpg

4.1.U2 Members of a species may be reproductively isolated in separate populations. AND 4.1.U7 A community is formed
by populations of different species living together and interacting with each other.
Population is a group of organisms of the same species that are living in the same area
at the same time.
Organisms of the same species separated geographically or temporally are
unlikely to breed, though the ability to do so remains. The separated
organisms are regarded as being members of different populations.
All organisms are dependent on interactions
with members of other species for survival, e.g.
a Lion depends on the availability prey species,
such as Zebra and Antelope.
Community is a group of populations that are living and interacting
together in the same area.
http://www.adventurewomen.com/wp-content/uploads/2015/04/WPanimals-at-watering-hole-at-Etosha.jpg
Communities also include plants and microbes
and hence often involve thousands of species.

Review: 4.3.U1 Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds. AND 4.1.U9
Autotrophs obtain inorganic nutrients from the abiotic environment.
http://commons.wikimedia.org/wiki/File:Plagiomnium_affine_laminazellen.jpeg
http://www.earthtimes.org/newsimage/photosynthesis-dream-renewable-energy_1_02842012.jpg
n.b. Although most autotrophs fix
carbon by photosynthesis. A few are
Chemoautotrophs and fix carbon by
utilising the energy in the bonds of
inorganic compounds such as hydrogen
sulfide.
All autotrophs convert carbon dioxide (from the atmosphere or dissolved in
water) into organic compounds.
Plant initially synthesis sugars (e.g.
glucose) which are then converted
into other organic compounds such
as:
• complex carbohydrates e.g.
starch, cellulose
• lipids
• amino acids
The inorganic nutrient compounds, e.g. water,
carbon dioxide, nitrates, phosphorous and oxygen are
obtained from the abiotic environment, whether it
be the soil, air or water.

4.1.U3 Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods).
Autotrophs synthesise their own organic
molecules and are therefore known as
producers
All organisms require organic molecules, such as amino acids, to carry out
the functions of life, for example metabolism, growth, and reproduction.
https://commons.wikimedia.org/wiki/File:Colpfl27a.jpg
Heterotrophs however obtain their
organic molecules from other
organisms
https://commons.wikimedia.org/wiki/File:Zebra_Grazing_
%289659709105%29.jpg

Nature of Science: Looking for patterns, trends and discrepancies - plants and algae are mostly autotrophic but some are
not. (3.1)
https://commons.wikimedia.org/wiki/File:Venus_Flytrap_showing_trigger_hairs.jpg
https://commons.wikimedia.org/wiki/File:Euglena_sp.jpg
Euglena sp. is a genus of Algae that will
photosynthesise (autotroph) in sufficient light,
feeding as an autotroph, but can also ingest
particles of food by phagocytosis, which it then
digests (heterotroph)
Venus flytrap (Dionaea muscipula) is
found in subtropical wetlands and like most
plants photosynthesise (autotroph), but
also traps and digests both insects and
spiders (heterotroph), to compensate for
the nutrient poor soil of the wetlands.
A few plants and algae use a combination of different modes of nutrition and are
hence known as mixotrophs

https://commons.wikimedia.org/
wiki/File:Zebra_Grazing_%289659
709105%29.jpg
4.1.U4 Consumers are heterotrophs that feed on living organisms by ingestion.
Heterotrophs that ingest other organisms obtain their organic molecules are
known as Consumers
Herbivores feed on
producers (e.g. deer,
zebra and aphids)
Consumers use a range of different food sources and
feeding mechanisms. The combination of food source and
feeding mechanism can be used to classify consumers.
Carnivores feed on other consumers
(e.g. lions, snake and ladybirds)
Omnivores feed on a
combination of both
producers and consumers
(e.g. chimpanzee, mouse)
https://commons.wikimedia.org/wiki/File:Lion_feedi
ng_-_melbourne_zoo.jpg
Scavengers are specialised carnivores
that feed mostly on dead and decaying
animals (e.g. hyenas, vultures crows)
https://commons.wikimedia.org/wiki/File:Vulture_-
_Sky_burial.jpg
https://commons.wikimedia.org/wiki/
File:Gombe_Stream_NP_Jungtier_fres
send.jpg

4.1.U5 Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
Humus is decaying leaf litter mixed with the soil
Detritivores are a type of heterotroph that obtain nutrients by consuming
non-living organic sources, such as detritus and humus
Detritus is dead, particulate organic matter. This includes
decaying organic material and fecal matter
Examples of detritivores include dung
beetles, earthworms, woodlice and crabs
https://commons.wikimedia.org/wiki/File:Earthworm.jpg

4.1.U6 Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
unlike most heterotrophs, saprotrophs are not consumers, as they do
not ingest food: digestion is external as enzymes are secreted.
https://commons.wikimedia.org/wiki/File:Gelbstieliger_Nitrathelmling_Mycena_renati.jpg
Saprotrophs live on, or in, non-living organic matter. They secrete digestive
enzymes on to the organic matter and absorb the products of digestion.
Examples of saprotrophs include bacteria and fungi
Because saprotrophs facilitate the
breakdown of organic material, they
are referred to as decomposers

4.1.S1 Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode
of nutrition.
Which group of organisms in the carbon cycle converts carbon into a form
that is available to primary consumers?
A. Decomposers
B. Saprotrophs
C. Detritus feeders
D. Producers
Classifying organisms based on their nutrition

4.1.S1 Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode
of nutrition.
Which group of organisms in the carbon cycle converts carbon into a form
that is available to primary consumers?
A. Decomposers
B. Saprotrophs
C. Detritus feeders
D. Producers
Classifying organisms based on their nutrition

4.1.S1 Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode
of nutrition.
Slime moulds (Acrasiomycota) are protoctists. They feed on decaying organic
matter, bacteria and protozoa. Which of the terms describes their nutrition?
I. Detritivore
II. Autotroph
III. Heterotroph
A. I only
B. I and II only
C. I and III only
D. I, II and III
Classifying organisms based on their nutrition

4.1.S1 Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode
of nutrition.
Slime moulds (Acrasiomycota) are protoctists. They feed on decaying organic
matter, bacteria and protozoa. Which of the terms describes their nutrition?
I. Detritivore
II. Autotroph
III. Heterotroph
A. I only
B. I and II only
C. I and III only
D. I, II and III
Classifying organisms based on their nutrition

4.1.S1 Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode
of nutrition.
The scarlet cup fungus (Sarcoscypha coccinea) obtains its nutrition from
decaying wood by releasing digestive enzymes into the wood and absorbing
the digested products. Which of the following terms describe(s) the fungus?
I. Autotroph
II. Heterotroph
III. Saprotroph
A. III only
B. II and III only
C. I and III only
D. I, II and III
Classifying organisms based on their nutrition

4.1.S1 Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode
of nutrition.
The scarlet cup fungus (Sarcoscypha coccinea) obtains its nutrition from
decaying wood by releasing digestive enzymes into the wood and absorbing
the digested products. Which of the following terms describe(s) the fungus?
I. Autotroph
II. Heterotroph
III. Saprotroph
A. III only
B. II and III only
C. I and III only
D. I, II and III
Classifying organisms based on their nutrition

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Testing for associations between species
species may be associated in different ways
Positive association Negative association No association
Species found in the same
habitat.
e.g. predator - prey,
herbivore & plant,
symbiosis
Species occur separately
in differing habitats.
e.g. competitive exclusion,
require different nutrients
Species occur as
frequently apart as
together.

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Testing for associations between species
Quadrat sampling can be used in a number of ways including:
• Estimation of population density/size
• Measuring the distribution of species
Quadrats are placed repeatedly in a sample area to provide a reliable
estimate. Quadrats can be placed systematically, e.g. in a ‘belt
transect’, typically to measure changing distribution, or randomly, e.g.
to estimate population density. Depending on what is being measured
either presence/absence, frequency or % coverage of a given species
can be recorded. Both systematic and random sampling methods are
used to avoid bias in the selection of samples.
The major limitation of quadrat sampling is that large and mobile animals cannot be
effectively sampled. It is most suitable for plants and small, slow moving animals.

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Data from: https://www.geography-fieldwork.org/ecology/hydrosere/4-data-analysis.aspx
https://c1.staticflickr.com/9/8678/15983466342_62a12ba53d_b.jpg
https://en.wikipedia.org/wiki/Galium_elongatum#/media/File:Galium_elongatum_eF.jpg
Two continuous belt transects were taken from the edge of a lake to 25m inland.
1m2 quadrats were used making a total sample of 100 quadrats. The presence or
absence of two species was recorded for each quadrat:
Within the 100 quadrats
sampled, 12 contained
both bottle sedge and
marsh bedstraw, 3
contained only marsh
bedstraw, 29 contained
only bottle sedge, and 56
contained neither species.
Testing for the association between two species using the Chi-
squared test
Bottle sedge (Carex
rostrata) is a swamp
plant
Marsh bedstraw (Galium
elongatum) is found in ditches
and wet meadows.
Is there an association
between the two species?

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Data from: https://www.geography-fieldwork.org/ecology/hydrosere/4-data-analysis.aspx
Complete the contingency table of
observed frequencies using the
data provided:
Testing for an association between two species using the Chi-
squared test
Observed
values
Marsh bedstraw
present absent total
Bottle
sedge
present 41
absent 59
total 15 85 100
Null hypothesis (H0): There is no significant difference between the
distribution of two species (i.e. distribution is random)
Alternative hypothesis (H1): There is a significant difference between the
distribution of species (i.e. species are associated)
First step in statistics is
ALWAYS to define the
hypotheses
1
2

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Data from: https://www.geography-fieldwork.org/ecology/hydrosere/4-data-analysis.aspx
Complete the contingency table of
observed frequencies using the
data provided:
Testing for an association between two species using the Chi-
squared test
Observed
values
Marsh bedstraw
present absent total
Bottle
sedge
present 12 29 41
absent 3 56 59
total 15 85 100
Null hypothesis (H0): There is no significant difference between the
distribution of two species (i.e. distribution is random)
Alternative hypothesis (H1): There is a significant difference between the
distribution of species (i.e. species are associated)
First step in statistics is
ALWAYS to define the
hypotheses
1
2

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Data from: https://www.geography-fieldwork.org/ecology/hydrosere/4-data-analysis.aspx
Testing for an association between two species using the Chi-
squared test
Observed
values
Marsh bedstraw
present absent total
Bottle
sedge
present 12 29 41
absent 3 56 59
total 15 85 100
Expected values Marsh bedstraw
present absent total
Bottle
sedge
present 41
absent 59
total 15 85 100
Calculate expected values using the
formula:
= row total x column total
grand total
3
Null hypothesis (H0): There is no significant difference between the
distribution of two species (i.e. distribution is random)
Alternative hypothesis (H1): There is a significant difference between the
distribution of species (i.e. species are associated)
n.b. Expected values are what you would
expect to be find if there is no association
between the species.

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Data from: https://www.geography-fieldwork.org/ecology/hydrosere/4-data-analysis.aspx
Testing for an association between two species using the Chi-
squared test
Observed
values
Marsh bedstraw
present absent total
Bottle
sedge
present 12 29 41
absent 3 56 59
total 15 85 100
Expected values Marsh bedstraw
present absent total
Bottle
sedge
present 6.15 34.85 41
absent 8.85 50.15 59
total 15 85 100
Calculate expected values using the
formula:
= row total x column total
grand total
3
Null hypothesis (H0): There is no significant difference between the
distribution of two species (i.e. distribution is random)
Alternative hypothesis (H1): There is a significant difference between the
distribution of species (i.e. species are associated)
n.b. Expected values are what you would
expect to be find if there is no association
between the species.

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Data from: https://www.geography-fieldwork.org/ecology/hydrosere/4-data-analysis.aspx
Testing for the association between two species using the Chi-
squared test
Observed
values
Marsh bedstraw
present absent total
Bottle
sedge
present 12 29 41
absent 3 56 59
total 15 85 100
Expected values Marsh bedstraw
present absent total
Bottle
sedge
present 6.15 34.85 41
absent 8.85 50.15 59
total 15 85 100
Null hypothesis (H0): There is no significant difference between the
distribution of two species (i.e. distribution is random)
Alternative hypothesis (H1): There is a significant difference between the
distribution of species (i.e. species are associated)
4
χ2 =
= (12 – 6.15)2 + … + (56 –
50.15)2
6.15 50.15
= 5.56 + 3.86 + 0.98 + 0.68
= 11.10
Calculate the Chi-squared value:

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Data from: https://www.geography-fieldwork.org/ecology/hydrosere/4-data-analysis.aspx
Testing for the association between two species using the Chi-
squared test
Observed
values
Marsh bedstraw
present absent total
Bottle
sedge
present 12 29 41
absent 3 56 59
total 15 85 100
Expected values Marsh bedstraw
present absent total
Bottle
sedge
present 6.15 34.85 41
absent 8.85 50.15 59
total 15 85 100
Null hypothesis (H0): There is no significant difference between the
distribution of two species (i.e. distribution is random)
Alternative hypothesis (H1): There is a significant difference between the
distribution of species (i.e. species are associated)
4
χ2 =
= (12 – 6.15)2 + … + (56 –
50.15)2
6.15 50.15
= 5.56 + 3.86 + 0.98 + 0.68
= 11.10
Calculate the Chi-squared value:

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Data from: https://www.geography-fieldwork.org/ecology/hydrosere/4-data-analysis.aspx
Testing for the association between two species using the Chi-
squared test
Observed
values
Marsh bedstraw
present absent total
Bottle
sedge
present 12 29 41
absent 3 56 59
total 15 85 100
Expected values Marsh bedstraw
present absent total
Bottle
sedge
present 6.15 34.85 41
absent 8.85 50.15 59
total 15 85 100
Null hypothesis (H0): There is no significant difference between the
distribution of two species (i.e. distribution is random)
Alternative hypothesis (H1): There is a significant difference between the
distribution of species (i.e. species are associated)
5 Determine the degrees of freedom:
Degrees of freedom (df)
= (rows* – 1) x (columns* – 1)
= (2 - 1) x (2 - 1)
= 1
n.b. for an association between two
species df ALWAYS = 1
*not including totals

4.1.S3 Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
AND 4.1.S4 Recognizing and interpreting statistical significance.
Data from: https://www.geography-fieldwork.org/ecology/hydrosere/4-data-analysis.aspx
Testing for the association between two species using the Chi-
squared test
df p (% certainty)
0.5
(50%)
0.1
(90%)
0.05
(95%)
0.01
(99%)
0.001
(99.9%)
1 0.455 2.706 3.841 6.635 10.827
2 1.386 4.605 5.991 9.21 13.815
3 2.366 6.251 7.815 11.345 16.268
4 3.357 7.779 9.488 13.277 18.465
5 4.351 9.236 11.07 15.086 20.517
Null hypothesis (H0): There is no significant difference between the
distribution of two species (i.e. distribution is random)
Alternative hypothesis (H1): There is a significant difference between the
distribution of species (i.e. species are associated)
6 Compare the χ2 value with the critical values
and validate the hypotheses:
Critical values for the χ2 distribution
• It is usual to consider a result
statistically significant at the 95%
certainty (p <0.05) level.
• As df = 1 that means the H0 is
rejected if X2 > 3.841
• Since 11.10 > 3.84 H0 is rejected and
H1 is accepted: there is an
association between Marsh
bedstraw and Bottle Sedge.
n.b. In this case 11.10 > 10.827 we can go
further and say that we are 99.9% certain
there is an association between the two
species.

4.1.U8 A community forms an ecosystem by its interactions with the abiotic environment.
http://www.slideshare.net/gurustip/communities-and-ecosystems

4.1.U10 The supply of inorganic nutrients is maintained by nutrient cycling.
Nutrient cycling
The supply of nutrients is limited
and therefore ecosystems
constantly recycle the nutrients
between organisms.
Elements required by an organism for growth and metabolism are
regarded as nutrients, e.g. carbon, nitrogen and phosphorous.
• Autotrophs convert nutrients
from inorganic form into
organic molecules, e.g. carbon
dioxide becomes glucose
• Heterotrophs ingest other
organisms to gain organic forms
of nutrients
• Saprotrophs breakdown organic
nutrients to gain energy and in
the process release nutrients
back into inorganic molecules,
e.g. fungi release nitrogen as
ammonia into the soil. This
ensures the continuing
availability of nutrients to
autotrophs.
http://www.ib.bioninja.com.au/_Media/nutrient-cycling_med.jpeg

4.1.U11 Ecosystems have the potential to be sustainable over long periods of time.
Ecosystems are sustainable
To remain sustainable an ecosystem requires:
• Continuous energy availability, e.g. light from the sun
• Nutrient cycling - saprotophs are crucial for continuous provision of nutrients to
producers
• Recycling of waste – certain by products of metabolism, e.g. ammonia from excretion,
are toxic. Decomposing bacteria often fulfill this role by deriving energy as toxic
molecules are broken down to, simpler, less toxic molecules.
Most flows of energy and nutrients in
an ecosystem are between members of
the biotic community. Relatively few
flows of energy and nutrients enter or
leave from surrounding ecosystems.
Therefore ecosystems are to a
large extent self-contained and
hence self-sustaining.
http://i.dailymail.co.uk/i/pix/2013/01/24/article-2267504-17212EB3000005DC-781_634x663.jpg

4.1.S2 Setting up sealed mesocosms to try to establish sustainability. (Practical 5)
Mesocosms are biological systems that contains the abiotic and biotic features of
an ecosystem but are restricted in size and/or under controlled conditions.
http://i.dailymail.co.uk/i/pix/2013/01/24/article-2267504-17212EB3000005DC-781_634x663.jpg
The restriction placed on mesocosms make them useful
for scientific investigations where the uncontrolled
nature of a natural ecosystems makes it difficult to collect
meaningful data.
The mesocosm in the image has survived for 53 years since being sealed in the bottle:
http://www.dailymail.co.uk/sciencetech/article-2267504/The-sealed-bottle-garden-thriving-40-years-fresh-air-water.html

4.1.S2 Setting up sealed mesocosms to try to establish sustainability. (Practical 5)
Mesocosms are biological systems that contains the abiotic and biotic features of
an ecosystem but are restricted in size and/or under controlled conditions.
http://i.dailymail.co.uk/i/pix/2013/01/24/article-2267504-17212EB3000005DC-781_634x663.jpg
Build your own mesocosm and blog the
changes you observe:
http://scribbit.blogspot.com/2010/05/kids-
summer-crafts-build-ecosystem.html
Learn more about mesocosms developed for
research:
• The biosphere -
http://archive.bio.ed.ac.uk/jdeacon/biosph
ere/biosph.htm
• Ecotron -
http://www3.imperial.ac.uk/cpb/history/th
eecotron

Bibliography / Acknowledgments