4.1 Species, communities and ecosystems

4.1. Species, communities and ecosystems
Miltiadis-Spyridon Kitsos
Platon IB Diploma
http://images.slideplayer.com/21/6279017/slides/slide_9.jpg

The official IB Diploma Biology guide
Essential idea: Ecosystems require a continuous supply of energy to fuel life processes and to replace
energy lost as heat.
https://ibpublishing.ibo.org/server2/rest/app/tsm.xql?doc=d_4_biolo_g
ui_1402_1_e&part=3&chapter=4

Organisms are never studied in isolation since they never live in isolation
http://www.smithlifescience.com/Girl_Mag
nifying_Glass.gif
http://images.cli
partpanda.com/c
row-clip-art-
COLOR_CROW.jp
g
http://images.clipartpanda.com/sun-clip-art-
7caKAXocA.gif http://images.clipartpanda.com/cloud-clipart-rain-cloud.png
http://clipartix.com/wp-
content/uploads/2016/04/Sweet
-corn-clipart-clipartcow.jpgInteractions among the individuals of
the same species
Interactions among the individuals of
different species (community)
Interactions with the abiotic environment

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

Species are groups of organisms that can potentially interbreed to produce fertile offspring.
http://bestanimations.com/Animals/Mammals/Hor
ses/horse-walking-gif-animation2.gif
Horse (Equus caballus)
Species: individuals may interbreed to produce
fertile offspring
For scientific names see 5.3. Classification
https://clipartion.com/wp-content/uploads/2015/11/vector-donkey-
donkey-free-vectors-download-4vector.png
Donkey (Equus africanus asinus)
Species: individuals may interbreed to produce
fertile offspring
Offspring
fertile
Offspring
fertile
https://s-media-cache-ak0.pinimg.com/564x/a8/c9/ea/a8c9ea92a0d8c1fdfd229f428c9d4d4c.jpg
Equus caballus and Equus africanus
are two distinct species since its
offspring
the mule, (Equus asinus x Equus
caballus) is not fertile

Emergence of new species is a result of reproductive isolation
https://ib.berkeley.edu/labs/wake/375_predict
ors_reprod_isolation_ensatina.pdf
https://pbs.twimg.com/profile_images/120252360/readmore-
logo_bigger_400x400.jpg
Read more
https://dmcastillo.files.wordpress.com/2012/09/speciation-diagram.jpg

Members of a species may be reproductively isolated in separate populations
http://victoriafalls24.com/wp-content/uploads/2013/07/Elephant-
044.jpg?a046ea
Population: individuals of the same species living at the same area at the same time

A wide geographical distribution of a species may imply genetic isolation but not necessarily
Discover the
distribution of
different species
at MOL: Map of
life

Populations under threat
http://cdn.modernfarmer.com/wp-content/uploads/2013/06/bee-hero.jpg
Since 2006 there is a gradual decrease in bee populations. Read the following
article and write a short paragraph outlining the reasons for this gradual
decrease. http://www.globalresearch.ca/death-and-extinction-of-the-bees/5375684
Read more

https://notexactlyrocketscience.files.wordpress.com/2006/10/nwh
i_-_french_frigate_shoals_reef_-_many_fish.jpg
Community is a group of populations that are living and interacting together in the same
area.
How many different species can you identify? Are all members of the
community visible? Can you identify possible ways of interaction?

https://notexactlyrocketscience.files.wordpress.com/2006/10/nwh
i_-_french_frigate_shoals_reef_-_many_fish.jpg
area.
http://fany.savina.net/wp-
content/uploads/2010/03/deerfight.jpg
http://www.asknature.org/images/uploads/strat
egy/fb410d8500af30a5daf5b647954b7fa5/10047
10143_54bd55e715_b.jpg

area.
In these series of videos, you may identify and
discuss examples of ecological and symbiotic
relationships in the ocean.
After watching the videos try to answer the revision
questions in the handout.

An ecosystem is a community and its interactions with the abiotic environment
http://news.wisc.edu/newsphotos/images/Carpenter_Refugee_Pi
c1_03.jpg
http://vignette2.wikia.nocookie.net/clubpenguin/images/f/f7/Sun_P
in.PNG/revision/latest?cb=20150313154846
Green plants (producers)
A population of fish
A bird population
Soil bacteria
Community
Solar energy from the sun
Ecosystems have no clear boundaries. They are delimited by the observer. In this sense, a pot with a plant and the
planet’s biosphere may be considered as distinct ecosystems.

An ecosystem is a community and its interactions with the abiotic environment
Ecosystems have no clear boundaries. They are delimited by the observer. In this sense, a pot with a plant and the
planet’s biosphere may be considered as distinct ecosystems.
Apply one or more of the terms shown below to
describe each of the listed features of a fresh water
lake
Ecosystem
Population
Community
Biomass
Abiotic factor
The whole lake
Water temperature
Mass of zooplankton
All the frogs of the lake
The mass of aquatic plants
See More
https://www.ted.com/talks/george_monbiot_for_more_wonder_rewild_the_worldhttps://www.youtube.com/watch?v=v6ubvEJ3KGM

Species have either an autotrophic or heterotrophic method of nutrition (a few species have
both methods).
All organisms need a supply or nutrients to carry out their fundamental processes (growth, metabolism, reproduction
etc).
There are two different types for obtaining these nutrients
Autotrophs (Self-feeding) Have the
ability to build their own carbon
compounds from C02 and simple
inorganic molecules.
They are also known as producers
Revision: Photosynthesis
http://s.hswstatic.com/gif/irrigation-photosynthesis.gif
Heterotrophs (Feeding from someone
else) Obtain their carbon compounds
from someone else
http://blakeandbrittanysecologyproject.wikispaces.com/file/view/be
ar-eating-salmon.jpg/290306133/445x280/bear-eating-salmon.jpg
Nature of science
The vast majority of plants are autotrophs and carry out
photosynthesis. However, 1% of plants may be parasitic,
hence heterotrophic.
Is this enough evidence to refute the pattern of
autotrophy in plants? Would your opinion change if the
percentage of parasitic species was higher?

Species have either an autotrophic or heterotrophic method of nutrition (a few species have
both methods).
However, there are organisms that may exhibit both heterotrophic and autotrophic nutrition. These species are
known as mixotrophic
https://upload.wikimedia.org/wikipedia/commons/e/ea/Euglena_diagram.jpg
The protist Euglena sp. is a
mixotrophic organism. It may
digest small food particles
(heterotrophic) but it can also
perform photosynthesis
(autotrophic). How can you
reckon that?
https://youtu.be/cirdBGQAnSQ?t=1m9s
Another example are the insect-
eating plants (you may call them
carnivorous)
https://i.ytimg.com/vi/-iHIKhKCg6E/maxresdefault.jpg
https://youtu.be/-iHIKhKCg6E

Consumers are heterotrophs that feed on living organisms by ingestion
Consumers ingest other organisms that are alive or have been dead for a short period of time. After ingestion food
is digested and the products of digestions are absorbed.
https://upload.wikimedia.org/wikipedia/commons/thumb/
7/7c/Scimitar_oryx1.jpg/800px-Scimitar_oryx1.jpg
Herbivores consume plant material
(producers)
Carnivores feed on other consumers
https://upload.wikimedia.org/wikipedia/commons/thumb/e/
eb/Young_lion_feeding_on_eland.jpg/800px-
Young_lion_feeding_on_eland.jpg
Scavengers feed on other consumers
that have been dead for a short time
(carcasses)
https://upload.wikimedia.org/wikipedia/co
mmons/3/3e/HyenasFeedFromCarcass.JPG
Omnivores
consume food of
both plant and
animal origin
https://upload.wikimedia.org/wikipedia/commons/thumb/e
/e0/Rat_Terrier_head.jpg/1280px-Rat_Terrier_head.jpg

Detritivores are heterotrophs that obtain organic nutrients from detritus by internal
digestion.
Detritivores ingest non-living organic matter and then digest it internally. Two very
characteristic examples of detritivores are earthworms and dung beetles. They would feed
on detritus (particulate non-organic matter) or humus (decaying plant litter)
https://i.ytimg.com/vi/Q1zbgd6xpGQ/maxresdefault.jpg
https://youtu.be/Zskz-iZcVyY
Kung Fu Dung Beetles

Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by
external digestion.
unlike detritivores, Saprotrophs ingest digested non-living
organic matter. Digestion is external via enzymes
secreted by the organism.
hhttps://yearinthewoods.files.wordpress.com/2013/05/img_4331
Certain types of bacteria and fungi belong to saprotrophs, also known as decomposers,
facilitating the conversion of dead organic matter to inorganic.

Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of
their mode of nutrition.
Classifying organisms based on their nutrition
http://www.nature.com/polopoly_fs/
7.8475.1358416025!/image/Palmer-
Fig%201.jpg_gen/derivatives/landsca
pe_300/Palmer-Fig%201.jpg
https://upload.wikimedia.org/wikipedia/commons/f/f1/Hyphae.JPG http://www.stephenshelleyphotography.com/pho
toblog/wp-
content/uploads/2012/01/IMG_6874.jpg
Acorn barnacles use their
appendages to filter
the marine water and
consume particulate matter
The species belongs to
___________________
This is a fungal mycelium made from
several hyphae. It belongs to a
fungal species
_________________________
Ghost orchids are epiphytes
depending their nutrition on an
association with ectomycchorizal
fungi that allows them to tap into
the plant stems and absorb the plant
sap.
_________________________
Venus fly traps are plant species
that may carry out photosynthesis
and also digest insects to get a
supply of nitrogen
_________________________
https://upload.wikimedia.org/wikipedia/com
mons/3/37/Venus_Flytrap_showing_trigger_h
airs.jpg

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
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

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

http://umaine.edu/leslie-lab/files/2010/03/rocky-shore-communitiy.jpg
An intertidal rocky shore community.
How many different species can you
spot?
Identify any of the ecological
interactions described before
Different communities may be found at different tidal
heights
A community is formed by populations of different species living together and interacting
with each other.

A community is formed by populations of different species living together and interacting
with each other.
Species of a community may exhibit an association. In this case their distribution in the habit is
more or less determined by their interaction. However, two species may not interact at all

Testing for association between two species using the chi-squared test with data obtained by
quadrat sampling
The Quadrat
For many years ecologists are using quadrat samplers to carry out fieldwork in communities.
Quadrat samplers are used to:count the number of individuals/ coverage of a certain species
in randomly generated samples.
Assess the distribution of species along a transect
https://www.wellswayschool.com/upload/organis
ms_and_environment_student_support.pdf

Using quadrats to test for association between
species
A quadrat represents the minimal sampling area that should
be sampled in order to get an accurate representation of a
population or community density.
It is only used for sessile organisms
http://www.sci.sdsu.edu/SERG/techniques/mfps/mfpsfig2
Look at the graph and decide which
factors are important for determining
the quadrat size in an area
https://upload.wikimedia.org/wikipedia/commons/5/
59/Quadrat_sample.JPG

quadrat sampling
Systematic vs random sampling
Systematic sampling: When quadrats are taken repeatedly in fixed internals along a line or
belt transect.Transect is set along areas where there are clear environmental gradients.
Line transect
A line that runs across the area of
study. Species presence absence is
recorded in fixed intervals
Belt transect
A belt that runs across the area of
study. Species presence absence as
well as abundance is recorded

quadrat sampling
Systematic vs random sampling
Random sampling: When quadrats are placed randomly in the sampling area in order to
estimate the abundance of a species/ number of individuals - coverage

Procedure
1. Map your area using a grid.
2. You will use this grid to select random
samples in order to reduce the sampling
bias
3. Use a random number generator to
choose either quadrat numbers or area
coordinates
http://www.countrysideinfo.co.uk/images/howto.1.gif
https://rgsbio09.wikispaces.com/file/view/quadrat.jpg/8399
3785/420x416/quadrat.jpg
quadrat sampling

Procedure
1. Sample the area using a quadrat of appropriate size.
2. Observer decides whether individuals on the quadrat
borders are “in” or “out”
Consider the following example
https://rgsbio09.wikispaces.com/file/view/quadrat.jpg/8399
3785/420x416/quadrat.jpg
http://ic.pics.livejournal.com/shiinglim/27113561/101682/101682
_original.jpg
http://cliparts.co/cliparts/kTM/nd5/kTMnd55bc.png
In certain cases when distinct individuals can not be counted the
percentage cover of plants is estimated using the quadrat
subdivision.
It Is evident that the quadrat sampling technique may be used
only with sessile organisms
quadrat sampling

In a study we need to establish the association between two species. It is evident that the association
between the two species will affect their distribution.
e.g. species with mutualistic interactions will tend to be close to each other while the opposite happens if
species are competing.
1 2 3 4 5 6 7 8 9
A
B
C
D
E
F
G
H
I
Step 1. Sample the area for the two species using an
appropriate quadrat placed randomly in the grid
(generate random coordinates)
quadrat sampling

Step 2 . After collecting data construct a contingency table of observed frequencies for the two species
in the quadrat sampled
Consider the following example
Species B
present
Species B
absent
Total
Species A
present
10 20 30
Species A
absent
20 30 50
Total 30 50 Grand total 80
Step 3. Apply the chi-squared test for an association between the two species
For an excellent revision on statistics check Stephen Taylor’s i-biology site http://i-biology.net/ibdpbio/statistical-analysis/
Also check this online statistics textbook http://onlinestatbook.com/2/index.htm
quadrat sampling

Step 3c . Se the Ho and H1 for the chi-squared test
Ho: the two species are distributed independently.
H1: the two species tend to be found together or apart as a result of their interaction
Step 3b . Calculate the expected frequency for each instance of the contingency table using the
following equation
Species B
present
Species B
absent
Total
Species A
present
11.25 18.75 30
Species A
absent
18.75 31.25 50
Total 30 50 Grand total
80
Observed frequencies in the example
contingency table used
quadrat sampling

Step 3d. Calculate the chi-squared value using the following formula
Species B
present
Species B
absent
Species A
present
11.25 18.75
Species A
absent
18.75 31.25
Species B
present
Species B
absent
Species A
present
10 20
Species A
absent
20 30
Observed frequencies Expected frequencies
quadrat sampling

Step 3e Calculate the degrees of freedom for this test
d.f. = (columns-1) x (rows -1) = (2-1) x (2-1) = 1
Step 3f Using the chi-squared table calculate the critical value for X2 at 95% confidence interval
Testing for association between two species using the chi-squared test
with data obtained by quadrat sampling

The confidence interval in any statistical test indicates the confidence in rejecting the Ho, thus
declaring results as statistically significant, while Ho is true.
A usual percentage of 5% is used (that is confidence is 95%). This percentage indicates that there is
5% probability that Ho is true although the test rejects the Ho and hence results are statistically
significant.
In other words my confidence in rejecting the Ho is 95%
In other cases when a higher level of confidence is required a percentage of 1% is used.
Remember that 5% is the minimum acceptable percentage.
Read more:
http://onlinestatbook.com/2/logic_of_hypothesis_testing/significance.html
ToK: How the word “significant” is used nowadays? Why the adverb “statistically” is added?
Recognising and interpreting statistical significance

Recognising and interpreting statistical significance
Step 3g Using the chi-squared table calculate the critical value for X2 at 95% confidence interval
7.8790.355
Since the calculated X2 value is less than the
critical X2 value, Ho may not be rejected and
thus the distribution of the species is most
probably random

The concept of the ecosystem
A community forms an ecosystem by its interactions with the abiotic environment
Abiotic
environm
ent
Temperature
Salinity
Rainfall
Name yours
Community
(organisms
living in an
area)
interactions
http://wallpaperswide.com/ocean_shore_waves-wallpapers.html
Ecosystem
Wave action exerts a significant impact
on the rocky shore intertidal communityThe ecosystem is a study system of complex interactions and
not an actual entity so its boundaries are defined by the
observer
http://static.guim.co.uk/sys-
images/Guardian/About/General/2012/4/3/1333468800200
/Does-having-pot-plants-in-008.jpg
http://earthobservatory.nasa.gov/IOTD/view.php?id=38889
Plant roots will hold
the soil in place
and prevent
erosion
http://s.hswstatic.com/gif/willow/root-info2.gif

Inorganic nutrients
Autotrophs and heterotrophs obtain inorganic nutrients from the abiotic environment.
http://s.hswstatic.com/gif/willow/root-info2.gif
Choose two bulk and two trace
elements and explain why they are
essential for organisms
http://biology-forums.com/gallery/9828_12_01_13_9_01_20.jpeg
https://upload.wikimedia.org/wikipedia/commons/thumb/f/f
e/Nitrogen_Cycle.svg/800px-Nitrogen_Cycle.svg.png
https://upload.wikimedia.org/wikipedia/commons/thumb/3/38/Carbon-cycle-full.jpg/128
Carbon-cycle-full.jpg

Sustainability of ecosystems
Ecosystems have the potential to be sustainable over long periods of time.
Environmental sustainability is the ability to maintain rates of renewable resource harvest, and non-
renewable resource depletion that can be continued indefinitely.
http://www.thwink.org/sustain/glossary/Sustainability.htm
Resources
Non-renewableRenewable
Solar energy
Air, wind
Water, Tides
Soil. Plants
Fossil fuels
Oil
Coal
Natural Gas
Metallic and non-
metallic Minerals
http://www.ted.com/talks/johan_rockstrom_let_the_environment_guide
_our_development?language=en
http://www.ted.com/talks/alex_steffen_sees_a_sustainable_future?l
anguage=en

Sustainability of ecosystems
Ecosystems have the potential to be sustainable over long periods of time.
What are the requirements for a sustainable natural ecosystem?
ecosystem
1. Source of energy
2. Supply of nutrients
3. Recycling of the waste products
Saprotrophs
http://i.dailymail.co.uk/i/pix/2013/12/09/articl
e-2520650-0E47BEA900000578-
375_306x446.jpg
Activity
Think of a plant in a pot. It may be
considered as an ecosystem.
1. Which is the source of energy?
2. How is the plant supplied with
nutrients?
3. How are the nutrients recycled in
the pot?

Practical 5: Setting up sealed mesocosms to try to establish
sustainability
Mesocosms are experimental enclosures which are designed to provide a limited body of space with close to
natural conditions, in which environmental factors can be realistically manipulated and their effect on
communities may be investigated.
Mesocosms may be experimentally manipulated to test for combination of factors thay may yield sustainability.
Read more:
A portal of information on mesocosm facilities worldwide http://mesocosm.eu
Ideas to get you started building your own mesocoms http://www.magzinr.com/user/D_Faure/mesocosm
http://www.magzinr.com/users/D_Faure/pics/p/pickchurc
om20130253-years-old-sealed-bottle-garden.jpg
http://www.ime.fraunhofer.de/en/business_areas_AE/Fate_Effects_Agrochem/HigherTie
rTests/_jcr_content/stage/image.img.jpg/AOe%20PS%2010%20b.1393516670823.jpg

4.1 Species, communities and ecosystems

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4.1 Species, communities and ecosystems