2.2 Communities and Ecosystems

A community = all the biotic (living) components of a habitat.

Tropical Rainforest is a community of plants, animals, bacteria, and fungi

Sloths are famous for their green coloration, a result of the algae that live in their hair and help provide camouflage

An Ecosystem = the community AND the physical environment it interacts with.

Ecosystems may be of varying sizes from a drop of water to an entire forest.

There are 3 key ecological concepts that are vital to your understanding of how everything else works:

• Respiration

• Photosynthesis

• Productivity

Respiration

• Is the conversion of organic matter into carbon dioxide and water in all living organisms, releasing energy

Respiration

• All living things must respire to get energy to stay alive• Respiration involves breaking down food, often in the form of glucose, to

release energy which is used in living processes.

• Much of the energy produced in respiration is heat energy which is released(dissipated) into the environment.

• This increases the entropy of the system while the organism maintains a relatively high level of organization (low entropy)

https://www.youtube.com/watch?v=00jbG_cfGuQ

Respiration

Photosynthesis

• Is the process by which green plants make their own food from water and carbon dioxide using energy from sunlight

Photosynthesis

• A transformation of light energy into chemical energy (glucose)• Glucose is then the starting point for the plant to make every other

molecule that it needs• Photosynthesis produces the raw material for producing biomass

Photosynthesis

• Green plants contain chloroplasts with the green pigment chlorophyll• In the chloroplasts the energy from sun is used to split water and combine

the hydrogen to carbon dioxide to create the glucose• The oxygen split from the water molecule is the waste product oxygen

Photosynthesis

• All plants respire• In the sunlight plants respire and photosynthesize• In the dark they only respire

• Compensation Point when all CO2 that plants produce in respiration is used up in photosynthesis, the rates of the two processes are equal and there is no net release of either O2 of CO2.

This ususally occurs at dawn or dusk when light intensity is not too high.

*The plant is neither adding biomass nor using it up to stay alive. It is just maintaining itself

https://www.youtube.com/watch?v=sQK3Yr4Sc_k

Photosynthesis

Food Chains, Trophic Levels and Food Webs

Food Chains• Food chain = the flow of energy from one organism to the

next• Shows the feeding relationships between species in an ecosystem• Arrows show the direction of energy flow

Trophic Levels• Trophic Level = feeding

level in a food chain.

Primary Producers (PP)• Two types of producers. Most producers are…Autotrophs

(green plants)• make their own food from CO2 and H2O using

sunlight (PHOTOSYNTHESIS!)

Primary Producers (PP)

• Provide energy for all other trophic levels

• Bind soil, stop soil erosion

• Supply nutrients to soil

• Habitat for other organisms

Other Producers

Chemosynthetic organisms• Make their own food from simple

compounds. Do not require sunlight. Often are bacteria found in deep oceans

• Two types of producers.

Primary Consumers (PC)•Heterotrophs

(feed on other organisms)

• Herbivores (consume PP)

• Populations controlled by negative feedback

• They also disperse seeds

Plants

herbivores

Primary Consumers (PC)

Secondary Consumers (SC)

•Heterotrophs (feed on other organisms)

• Carnivores and Omnivores

• Consume herbivores and other carnivores, sometimes eat primary producers

Secondary Consumers (SC)

• Pollinate flowers

• Remove old and diseased animals from population

Secondary Consumers (SC)

Tertiary Consumers (TC)

•Heterotrophs (feed on other organisms)

• Top Carnivores and Omnivores

• Consume herbivores and other carnivores, sometimes eat primary producers

Tertiary Consumers (TC)

• Remove old and diseased animals from population

Decomposers •Get their energy from dead organisms

• Bacteria and fungi

• Secrete enzymes that break down the organic matter in dead organisms

Decomposers •Crucial role in the ecosystem!! They are tiny but important!

•Break down dead organisms

•Release nutrients back into the cycle

•Control the spread of disease

Detritivores•Get their energy from detritus

•Detritus = decomposing organic material (dead organisms, feces, or parts of an organism)

• Ex: crabs, worms, beetles, mites

Detritivores

•Break down dead organisms

•Release nutrients back into the cycle

•Control the spread of disease

Crucial role in the ecosystem!!

Food Webs• In ecosystems, there are many

food chains that are interconnected.

• Limits of food chains – only show each organism eating one other organism. In reality, organisms eat many other species as food!

•Food webs = complex network of interrelated food chains in an ecosystem

Food Webs• Arrows point towards the

direction of energy flow (arrow goes into the organism that is eating it)

• Show the complex feeding relationships that trophic pyramids and food chains cant show.

• (ex. A grizzly bear is a top predator but also eats plants)

Food Webs• Read and annotate Arctic Food Web article.

• Create a food web using only the animals mentioned in the article.

• Use the cut outs and a large whiteboard to draw arrows between the organisms.

• After you have made the food web, color code each organism as:

• Tertiary consumer• Secondary consumer• Primary consumer• Primary producer• Decomposers• Detritivores

3 types of ecological pyramids

• Your challenge:

• Design a poster that contains all 3 ecological pyramids

• They must have explanations that are easy to understand

• Visuals

• Units of measure

• Advantages and disadvantages of each

• Everyone in the group must be able to explain these pyramids

• Use your textbook pages 71-74

• The internet/videos

• My PPT on the class website

• Ecological Pyramids- include pyramid of numbers, biomass, and productivity and are quantitative models and are usually measured for a given area and time.• They allow easy examination of energy transfers and losses

• They display what feeds on what and what organisms exist at different trophic levels

• Demonstrate that ecosystems are systems in balance

Pyramid of numbers• Constructed by counting the number of organisms at each trophic

level.

• Samples from an area are used and the results multiplied to represent the whole.

Pyramid of numbers• The length of each bar gives a measure of the relative numbers

• Pyramids have producers at the bottom, usually in the greatest number.

• The bottom usually has many individuals in the producer, but some may have a large single plant or tree as a producer so the base is one individual which supports many consumers.

Pyramid of numbers

• Advantages: A simple easy method of giving an overview and is good for comparing changes in a population numbers over different times or seasons

• Disadvantages: • All organisms are included regardless of their size, therefore a pyramid based on

an oak tree would have a narrow base and get larger as it goes up the trophic levels.

• Does not allow for juveniles or immature forms

• Numbers can be too great to represent accurately

Pyramid of biomass

• Biomass is the quantity of dry organic material in an organism,

• It can also be measured for a population, a particular trophic level, or an ecosystem

• In a pyramid of biomass, it is the dry material of all organisms at that trophic level. (mass of each individual x # of individuals)

• Units of biomass = mass = _g_

• area m2 (land) g m-2

g/m3 for volumes of water shown like this g m-3

• Units can be energy content = J (joules)

Pyramid of biomass

• More likely to be pyramid shaped

• Exceptions include oceanic ecosystems – producers are phytoplankton. Phytoplankton reproduce fast but are present in small amounts at one time.

• Remember that a pyramid only represents a certain time (e.g. winter)

15.0 g

8.0 g

3.0 g

0.8 g

Draw a pyramid of biomass with calculations from the pyramid of numbers. You are solving for an area on land measured out by meters.Your answers should have gm-2

Pyramid of numbers

Average mass of organism X Number of organisms

Pyramid of Biomass• Advantages: takes account of the size of organisms, so it overcomes some

problems of pyramid of numbers

• Disadvantages:

• difficult to measure accurately because sampling involves killing of organisms

• Seasonal variation leads to inverted pyramids (e.g. less phytoplankton in winter)

• Some animals have a lot of bone or shell which can distort the results (e.g. a turtle’s shell has a large mass, but cannot be eaten for energy)

• Like pyramid of numbers it is a snapshot in time and place.

Pyramid of biomass

Pyramid of productivity

• Most accurate way to model an ecosystem• Shows the flow of energy through each trophic level usually over a

years time• Shows the energy or biomass being generated and available as food

to the next trophic level

Pyramid of productivity

• Units are measured in: energy per area per time

• It is saying, how much energy (J) is produced

in 1 m2, over a 1 year period.

• SHOULD be written as J m-2 yr -1

energy

area

time

joules

m2

year 1 m2

Pyramid of Productivity

• Always pyramid shaped in healthy ecosystems as they must follow the second law of thermodynamics

Pyramid of productivity• Shows how much energy is transferred from one trophic level to another.

• This is the energy pyramid you have been used to seeing!

• In the pyramid • There are 10,000 J of energy produced

by plants living in 1 m2, per year

10,000 J m-2 y-1

1,000,000 J m-2 y-1

1,000 J m-2 y-1

100 J m-2 y-1

10 J m-2 y-1

Pyramid of productivity10% of energy goes to the herbivores

10,000 J m-2 y-1

1,000,000 J m-2 y-1

J m-2 y-1

J m-2 y-1

J m-2 y-1

10 %

20 %

5 %Solve for this pyramid. Not all transfers are exactly 10%. Use the above formula to solve for the missing boxes. The transfer for the producers to the herbivores has been done.

= 1,000

1,000

2 super markets cannot be compared by just looking at the cereal on the shelves. The rate at which goods are being stocked and sold needs to be known.

Both may have well stocked shelves but the rate of removal of goods from a major city shop may be considerably more than from a village shop.

Pyramid of biomass represent the just the stock on the shelf at a given time, whereas pyramids of productivity show the rate at which that stock is being removed by customers and restocked by employees.

Pyramid of productivity

Advantages:

• Most accurate system, shows the actual energy transferred and allows for the rate of production

• Allows for comparison of ecosystems based on relative energy flows

• Pyramids are never inverted

• Energy from solar radiation can be added

Disadvantages:

• Data is difficult to collect as rate of biomass production over time must be measured

• Many species feed at more than one trophic level (true for all pyramids) so assigning them to on trophic level is difficult

• Construct the 3 pyramids on graph paper

• Page 74

2.2Consequences of Ecological

Pyramids

How the structure of the ecological pyramid affects the ecosystem

• The structure of ecological pyramids has consequences that can be seen in the way an ecosystem functions.

1. Concentration of toxic substances in the food chain

• If a chemical in the environment breaks down slowly, or does not break down at all, it will accumulate in organisms.

• POPs = persistent organic pollutants• Common chemicals: pesticides, heavy metals like Mercury

• Two ways chemicals can accumulate:

•Bioaccumulation

•Biomagnification

Bioaccumulation• Bioaccumulation = when a chemical builds up in a single organism over time

• What types of organisms would be most at risk for bioaccumulation?• Animals that eat more, are larger, and have longer lifespans

As the fish get older, and eat more, they will build up more chemicals in their bodies.

Bioaccumulation• How does it happen?

• The chemical accumulates because it does not break down easily

• The chemical gets stored in fat cells of organisms.

Biomagnification

• Biomagnification = the tendency of toxins to concentrate in organisms at higher trophic levels.

Biomagnification• Concentration of the chemical

at lower trophic levels may not have much effect

• But, as you go up the trophic pyramid, the highest levels will have very high amounts of the chemical

Biomagnification• How does it happen?

• Pollutants get into the producers (through water or air)

• Small herbivores eat many producers, and may also get the chemical through water.

• Carnivores eat many herbivores, and get even more of the chemical in their bodies. They take in so much of the chemical that it causes disease or death.

Video on Biomagnification of DDT

• https://www.youtube.com/watch?time_continue=2&v=uhiCORNRgzA

What other historical events have resulted in biomagnification?• Class discussion

• (Minamata Bay, Bhopal Disaster, etc)

Difference between Bioaccumulation and Biomagnification

Same organism has toxin build up in its body over time

Amount of toxin increases in higher trophic levels

Bioaccumulation

Biomagnification

Bioaccumulation or biomagnification?

Bioaccumulation or biomagnification? In the polar bear?

In the ecosystem?

In the seal?

2. Food chains have a limited length• Food chains cannot go on forever.

• Eventually the energy available runs out.

• WHY?• Only 10% of available energy makes

it to the next trophic level.

2. Food Chains have a Limited Length

• The 90% of energy that is lost as heat…what was it used for?• Respiration to keep the organism alive

• Herbivores destroying plants as they trample it

• Plant material that can’t be eaten (e.g. only eat the leaves of trees, not the wood)

• Energy to move

2. Food Chains have a limited length• How many trophic levels can a food chain have?

Terrestrial: 4 levels Aquatic: 5 levels

4

3

2

1

5

4

3

2

1

2. Food Chains have a Limited Length• Why do aquatic ecosystems have more

trophic levels than terrestrial ecosystems?

•Aquatic organisms don’t have to use as much energy to MOVE and MAINTAIN their bodies• They have the water holding

them up!

3. Top Carnivores are Vulnerable

• Highest level is most susceptible to changes in ecosystem…

• Top carnivores require more territory

• Ex. Clouded leopards in Borneo rainforests• # of leopards declining due to deforestation for palm oil (destroying territory and prey)

• Top carnivores have a limited diet, and need to eat lots of food to survive• If a source of food is destroyed, has a larger effect

• There are few top carnivores to begin with• Small populations are more at risk