2.2. Communities and Ecosystems

Miltiadis Kitsos

Platon school IB diploma

https://goo.gl/forms/7Gm5lnMCEi161eaz1

Significant ideas

• The interactions of species with their environment result in energy and nutrient

flows.

• Photosynthesis and respiration play a significant role in the flow of energy in

communities.

• The feeding relationships of species in a system can be modelled using food chains,

food webs and ecological pyramids.

Knowledge and understanding

• A community is a group of populations living and interacting with each other in a

common habitat.

• An ecosystem is a community and the physical environment with which it interacts.

• Respiration and photosynthesis can be described as processes with inputs, outputs

and transformations of energy and matter.

• Respiration is the conversion of organic matter into carbon dioxide and water in all

living organisms, releasing energy. Aerobic respiration can be represented by the

following word equation.

glucose + oxygen → carbon dioxide + water

Knowledge and understanding

• During respiration, large amounts of energy are dissipated as heat, increasing the

entropy in the ecosystem while enabling organisms to maintain relatively low entropy

and so high organization.

• Primary producers in most ecosystems convert light energy into chemical energy in

the process of photosynthesis.

• The photosynthesis reaction is can be represented by the following word equation.

carbon dioxide + water → glucose + oxygen

• Photosynthesis produces the raw material for producing biomass.

• The trophic level is the position that an organism occupies in a food chain, or the

position of a group of organisms in a community that occupy the same position in food

chains.

• Producers (autotrophs) are typically plants or algae that produce their own food using

photosynthesis and form the first trophic level in a food chain. Exceptions include

chemosynthetic organisms that produce food without sunlight.

• Feeding relationships involve producers, consumers and decomposers. These can be

modelled using food chains, food webs and ecological pyramids.

Knowledge and understanding

• Ecological pyramids include pyramids of numbers, biomass and productivity and are

quantitative models that are usually measured for a given area and time.

• In accordance with the second law of thermodynamics, there is a tendency for

numbers and quantities of biomass and energy to decrease along food chains;

therefore, the pyramids become narrower towards the apex.

• Bioaccumulation is the build-up of persistent or non-biodegradable pollutants within

an organism or trophic level because they cannot be broken down.

• Biomagnification is the increase in concentration of persistent or non-biodegradable

pollutants along a food chain.

• Toxins such as DDT and mercury accumulate along food chains due to the decrease

of biomass and energy.

• Pyramids of numbers can sometimes display different patterns; for example, when

individuals at lower trophic levels are relatively large (inverted pyramids).

• A pyramid of biomass represents the standing stock or storage of each trophic level,

measured in units such as grams of biomass per square meter (g m–2) or Joules per

square meter (J m-2)(units of biomass or energy).

Knowledge and understanding

• Pyramids of biomass can show greater quantities at higher trophic levels because

they represent the biomass present at a fixed point in time, although seasonal

variations may be marked.

• Pyramids of productivity refer to the flow of energy through a trophic level, indicating

the rate at which that stock/storage is being generated.

Knowledge and understanding

• Pyramids of productivity for entire ecosystems over a year always show a decrease

along the food chain.

Applications and skills

• Construct models of feeding relationships—such as food chains, food webs and

ecological pyramids—from given data.

• Explain the transfer and transformation of energy as it flows through an ecosystem.

• Analyse the efficiency of energy transfers through a system.

• Construct system diagrams representing photosynthesis and respiration.

• Explain the relevance of the laws of thermodynamics to the flow of energy through

ecosystems.

• Explain the impact of a persistent or non-biodegradable pollutant in an ecosystem.

Community & Ecosystem

A community is a group of populations living and interacting with each other in a

common habitat whereas,

An ecosystem is a community and the physical environment with which it interacts.

Species 1 Species 2

Species 3

Abiotic environment

Some notes on ecosystems

Ecosystems are units of study thus, the size is delimited by the investigator. Hence, they

may be of varying sizes, ranging from a drop of water to a pot with a flower to a rainforest.

Ecosystems do not exist independently but interact to make up the biosphere.

Biosphere is the part of the Earth and its atmosphere where living organisms exist, including

parts of the lithosphere, the hydrosphere and the atmosphere. Also called ecosphere.

http://www.tabletsmanual.com/img/wiki/drop_of_water.jpg

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Types of ecosystems

There are three main types of ecosystems:

• Marine

• Terrestrial

• Freshwater

http://www.laboratoryequipment.com/sites/laboratoryequipment.com/files/legacyimages/Resources/Laboratory_News/032612_fisheries.jpg

http://danielisland.com/wp-content/uploads/2017/03/Salt-Marsh.jpg

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Types of ecosystems

There are three main types of ecosystems:

• Marine

• Terrestrial

• Freshwater

http://blogs.dctc.edu/laht/files/2009/12/csprairietwolg.jpg

http://danielisland.com/wp-content/uploads/2017/03/Salt-Marsh.jpg

http://cdn-image.travelandleisure.com/sites/default/files/styles/1600x1000/public/1498168552/el-yunque-national-rainforest-tropical-puerto-rico-TROPICALPLANTS0617.jpg?itok=AY97tSbV

Prairie

Taiga

Rain

forest

Types of ecosystems

There are three main types of ecosystems:

• Marine

• Terrestrial

• Freshwater

http://justfunfacts.com/wp-content/uploads/2016/05/yangtze-river.jpg

https://upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Ugandan_fishing_boats.jpg/1280px-Ugandan_fishing_boats.jpg

http://cdn-image.travelandleisure.com/sites/default/files/styles/1600x1000/public/1498168552/el-yunque-national-rainforest-tropical-puerto-rico-TROPICALPLANTS0617.jpg?itok=AY97tSbV

Yangtze

River, China

Lake Victoria,

Uganda

Lake Victoria,

Uganda

Respiration and photosynthesisPrimary producers in most ecosystems convert light energy into chemical energy in the process of

photosynthesis.

Photosynthesis produces the raw material for producing biomass.

Photosynthesis is a biological process, carried out by autotrophs (e.g., plants) which use

solar energy to synthesize complex biological molecules such as glucose, from simpler

molecules that is, carbon dioxide and water.

https://dr282zn36sxxg.cloudfront.net/datastreams/f-d%3A3a8b868ced61d4b45f5c32edabc96e70bb5f8878a26a806286eed92c%2BIMAGE_THUMB_POSTCARD_TINY%2BIMAGE_THUMB_POSTCARD_TINY.1

For this purpose, photosynthetic pigments

such as chlorophyll are used which have the

ability to “trap” the sunlight and convert it to

chemical energy.

https://media1.shmoop.com/images/biology/biobook_photosyn_6.png

Respiration and photosynthesisThe photosynthesis reaction can be represented by the following word equation. carbon

dioxide + water → glucose + oxygen

6C02 + 6H2O C6H1206 + 6O2

chlorophyll

Carbon dioxide + water glucose +oxygen

Reactants Products

Photosynthesis

Respiration and photosynthesis can be described as processes with inputs, outputs and transformations of

energy and matter.

Solar energy is transformed in stored chemical energy.

Respiration and photosynthesisRespiration is the conversion of organic matter into carbon dioxide and water in all living organisms,

releasing energy.

Cellular respiration is a biological process where complex biological molecules are broken

down to carbon dioxide and water, releasing energy which is used for the energy

requirements of the organisms.

Energy is required for processes like movement, nutrition, excretion etc.

https://www.exploringnature.org/graphics/biology/cellular_respiration2_72.jpg

The process is carried in the cell’s

mitochondria.

https://media1.shmoop.com/images/biology/biobook_photosyn_6.png

Respiration and photosynthesisAerobic respiration can be represented by the following word equation.

glucose + oxygen → carbon dioxide + water

6C02 + 6H2OC6H1206 + 6O2

Carbon dioxide + waterglucose +oxygen

Reactants Products

Cellular respiration

Respiration and photosynthesis can be described as processes with inputs, outputs and transformations of

energy and matter.

Cellular respiration

The coupling between photosynthesis and respiration

Producers Primary producers in most ecosystems convert light energy into chemical energy in the process of

photosynthesis.

Producers have a key role in any ecosystem since they have the ability to trap the solar

energy and utilize it in order to convert simple inorganic molecules into living matter.

Since they rely entirely on themselves for meeting their energy needs they are called

autotrophs (the self-feeders)

http://www.goldiesroom.org/Multimedia/Bio_Images/05%20Nutrition/01%20Photosynthesis.gif

https://med-algae.com/wp-content/uploads/2017/08/algae-types.jpg

https://c1.staticflickr.com/3/2235/2401285296_57f4963b2d_b.jpg

Plants, algae and bacteria belong to this

groups

Photoautotrophs vs chemoautotrophsProducers (autotrophs) are typically plants or algae that produce their own food using

photosynthesis Exceptions include chemosynthetic organisms that produce food without

sunlight.

http://1.bp.blogspot.com/-RaE_tt57MT4/TiM0-w5wKwI/AAAAAAAADV0/Rn9TF20Z1Qk/s1600/hydrothermal+vents1.jpg

https://userscontent2.emaze.com/images/223af43b-4931-477f-bfc3-5c372ab39bfc/a046d5deeb2c0a8ca143815a44ab180f.jpg

http://www.marine-biotechnologie.de/files/images/riftia_1.gif

Most autotrophs are photoautotrophs meaning they use

solar energy are they main source of energy

Some bacteria are chemoautotrophs, meaning they use

chemical energy to convert simple molecules into

sugars.

A very good example are the chemosynthetic bacteria

living in a symbiotic relationship with giant tube worms

in deep sea vents.

ConsumersConsumers are heterotrophs that feed on living things by ingestion. They take in indigestedorganic material from consumers or producers.

Organisms that are unable to produce their own food and need other organisms to obtain energy and matter.

This is the reason they are called heterotrophs.

https://www.youtube.com/watch?v=xd8r9pf27v0

https://www.youtube.com/watch?v=79RvGRUdnwE

Limpet (Patella vulgata) foraging on kelp. Limpets belong to consumers.

DecomposersDecomposers obtain food and nutrients from the breakdown of dead organic matter

The decomposition of dead organic material releases nutrients which are again available in the ecosystem, mainly to the producers.

http://ww2.rspb.org.uk/Images/earthworms_tcm9-91592.jpg?width=768&height=432&crop=auto

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiX65imnInYAhUEOJoKHTCVAKUQjRwIBw&url=https%3A%2F%2F8ksfdeciduousforest.weebly.com%2Fsoil.html&psig=AOvVaw0F_t1xHF4DdEJCryU-eQRC&ust=1513331222736340

Thus decomposers have a major role in the recycling of matter to the ecosystems

They also contribute to the formation of the humus layer (decomposed organic matter)which retains:• nutrients in the soil.• humidity

Food chainsThe trophic level is the position that an organism occupies in a food chain, or the position of a group of

organisms in a community that occupy the same position in food chains.

A food chain is a graphical representation of the trophic relations between certain

species in an ecosystem. The arrows indicated the unidirectional flow of energy and

matter.

Eaten byEaten byEaten by

Food chains always begin with the producers (usually photosynthetic organisms),

followed by primary consumers (herbivores), secondary consumers and so one

Trophic levelThe trophic level is the position that an organism occupies in a food chain, or the position of a group of

organisms in a community that occupy the same position in food chains.

Food websFood webs are a more realistic representation of the feeding relations

The diets of most species are not limited to only one species. Quite the opposite,

since:

• They are seasonal changes in a diet.

• Most species do not belong to only one trophic level.

• There are developmental changes in diets.

In this image, identify the number of

food chains

and comment on the trophic level that

humans belong.

http://schoolbag.info/biology/humans/humans.files/image469.jpg

Food websFood webs are a more realistic representation of the feeding relations

Thus, food webs are complex networks of interrelated food chains.

You need to be able to:

Identify the length of all food

chains

Identify the trophic level of all

species involved

New equilibrium points if the

population of one or more

species change.

Efficiency of energy transfers within an ecosystem

Analyse the efficiency of energy transfers through a system.

All ecosystems on earth are open ecosystems supported by solar energy. The energy

is transformed to chemical energy by producers and then it flows through the living

components.

As you remember from topic 1, these transformations of energy are never 100%

efficient so much of the energy is transformed into heat.

Efficiency of energy transfers within an ecosystem

Analyse the efficiency of energy transfers through a system.

Describe the main transfers and transformations in this system’s diagram.

Ecological pyramidsEcological pyramids include pyramids of numbers, biomass and productivity and are quantitative

models that are usually measured for a given area and time.

These graphical models

demonstrate the feeding

relationships in an ecosystem

in a quantitative manner.

The surface area of each

square is indicative of the

energy, biomass, or, population

numbers.

KJ m-2 y-2Producers

Primary consumers

Secondary consumers

Tertiary consumers

Mind the units

Quantitative data for each trophic level are

drawn to scale as horizontal bars arranged

symmetrically around a central axes.

Pyramids of numbers Ecological pyramids include pyramids of numbers, biomass and productivity and are quantitative models that

are usually measured for a given area and time.

Each trophic level represents the number of individuals coexisting in an

ecosystem. Following the second law of thermodynamics the number of

individuals will be decreasing and hence, the pyramid would be narrower towards

the apex.

Producers

Prim. consumers

Sec. consumers

Tert. consumers

Number of individuals

Inverted pyramids of numbers. In

certain ecosystems, the number of

individuals at the producer level is

much lower that at the next trophic

level (e.g., in a woodland ecosystem

the number of trees is much lower than

the number of herbivorous insects)

resulting in a pyramid being upside-

down.

Pyramids of biomassEcological pyramids include pyramids of numbers, biomass and productivity and are quantitative models that

are usually measured for a given area and time.

Pyramids of biomass can show greater quantities at higher trophic levels because they represent the biomass

present at a fixed point in time, although seasonal variations may be marked

A pyramid of biomass represents the amount of (dry) organic material at each

trophic level.

Units: g m-2 or kg m-2

Producers

Prim. consumers

Sec. consumers

The usual shape is pyramid but with some exceptions, as for example, in marine ecosystems where phytoplankton (producers) is usually represented by small biomass at each time interval. Thus, at ant specific time interval x, phytoplankton may have a smaller biomass than zooplankton (secondary consumers)

340

17

0.85

173 Phytoplankton

Zooplankton

Pyramids of productivityEcological pyramids include pyramids of numbers, biomass and productivity and are quantitative models that

are usually measured for a given area and time.

A pyramid of productivity does not represent the standing stock but the rate at

which biomass or energy flow in the ecosystem.

They are always pyramid shaped .

Units are J m-2 yr-1 or gr m-2 yr-1

They are a better tool for comparing the energy flow in two ecosystems.

https://qph.ec.quoracdn.net/main-qimg-dd3e8f2c464a21ca080ffc4e47a3117f

An example from stores Pyramids of productivity refer to the flow of energy through a trophic level, indicating the rate at which that

stock/storage is being generated.

You can not compare the sales of two supermarkets by just looking at their

shelves.

The turnover rate, that is the speed by which a shop sell its products in relation to

stocks needs to be known.

This shop (image) may have already sold

the stocked products but to the eyes of

An observer it may be a shop having a very

low rate of sales.

Likewise, a pyramid of biomass depicts the

standing stock of organic mater at a given time,

while a pyramid of productivity describes the

turnover rate.

https://qph.ec.quoracdn.net/main-qimg-dd3e8f2c464a21ca080ffc4e47a3117f

https://upload.wikimedia.org/wikipedia/commons/5/5b/Empty_supermarket_shelves_before_Hurricane_Sandy%2C_Montgomery%2C_NY.jpg

173 Phytoplankton

Zooplankton

Constructing an ecological pyramid Pyramids of productivity refer to the flow of energy through a trophic level, indicating the rate at which that

stock/storage is being generated.

Producers 500 x 103 J m-2 yr-1

1st class consumers

50 x 103 J m-2 yr-1

2nd class consumers

5 x 103 J m-2 yr-1

1. Draw a rectangle for the the producers,

found at the bottom; indicate trophic

level and values with appropriate units.

2. On top of producers draw a rectangle

for 1st class consumers. Size should be

proportionate to value differences.

3. Continue with rest of trophic levels.

producers

50 x 103 J m-2 yr-1

500 x 103 J m-2 yr-1

1st class consumers

2nd class consumers 5 x 103 J m-2 yr-1

Bioaccumulation across trophic levels Bioaccumulation is the build-up of persistent or non-biodegradable pollutants within an organism or trophic

level because they cannot be broken down.

Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants along a food

chain.

Toxins such as DDT and mercury accumulate along food chains due to the decrease of biomass and energy.

Biomass DDT mass

Concentration

2nd class consumers

1 kg 1 mg 1 mg/kg

1st class cons

100 kg 1 mg 1 x 10-2 mg/kg

Producers 10,000 kg 1 mg 1 x 10-5 mg/kg

Consider this food chain

Since the biomass decreases and the mass of the non-biodegradable substance remains unchanged, the concentration of the non-biodegradable substance will increase up the food chain (biomagnification)

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Case study: The Bald eagle

The bald eagle (Haliaetus leucocephalus), once common throughout

most of North America, was reduced to as few as 400 nesting pairs

in the lower 48 United States by the 1960s.

The decline of the bald eagle was caused primarily by habitat loss

and widespread use of the pesticide DDT.

Toxins accumulated in the fatty tissues of adult eagles and caused

the females to lay eggs with shells too thin to survive.

Eggs were usually crashed by hutching mothers.

This is a very good example of a top predator (top of the food chain)

suffering from the biomagnification of a non-biodegradable pesticide.

The bald eagles were consuming smaller preys for long periods of

time thus accumulating DDT in their fatty tissues.

http://www.bagheera.com/wp-content/uploads/2014/01/bald_eagle_2011.jpg

https://goo.gl/images/uSVAfg

Case study: Minamata bay

• Minamata is a small town in Japan, known for the Chisso

factory producing fertilizers and plastics.

• Between 1932 and 1968, Chisso factory released more

than

• 20 tones of mercury and methylmercury in Minamata Bay.

• In the early 50s, people in the Minamata area started

suffering from mercury poisoning, due to the consumption

of seafood, mainly shellfish, that had been accumulating

mercury.

https://www.google.gr/maps/place/Minamata,+Kumamoto+Prefecture,+Japan/@32.6115314,130.619745,5z/data=!4m5!3m4!1s0x353fa336b868fd75:0xbcbb57ce5b5109de!8m2!3d32.2145158!4d130.4073698?hl=en

https://www.canada.ca/content/dam/eccc/migration/main/mercure-mercury/D721AC1F-4446-4E44-A13E-3845A7FAF7D7/i-f-bom-e.jpg

http://america.aljazeera.com/content/ajam/articles/2014/8/29/grassy-narrows-mercuryminimata/jcr:content/headlineImage.adapt.1460.high.minamata_japan_ontario_082914.1411404893479.jpg

Top carnivores

• In any food chain, top carnivores usually have small numbers due to the limited available energy

and thus, biomass.

• Furthermore, their diets are usually limited and thus any change in their food prey has a strong

effect on their survival rates. Thus, top carnivores are less resilient to change.

• Bioaccumulation and biomagnification also pause the populations of the top predators to a risk.

• Case study: Crash of the peregrine falcon populations in the UK during the 50s due to the

extensive use of DDT. After the non-biodegradable chemical were banned in the 60s the

populations started to recover.

https://res.cloudinary.com/dk-find-out/image/upload/q_80,w_1920,f_auto/Food_web_keclt8.jpg

https://youtu.be/QTV3XFHzvT4

References

Andrew, Davis, et al. Pearson Baccalaureate Environmental Systems And Societies For The Ib Diploma.

Rutherford, Jill. Environmental Systems and Societies. Oxford University Press, 2015.