Chapter 54

Chapter 54Chapter 54

Ecosystems (all organisms living in Ecosystems (all organisms living in a community as well as all the a community as well as all the abiotic factors they interact with.abiotic factors they interact with.

Ecosystem EcologyEcosystem EcologyEmphasizes:Emphasizes:

1.) 1.) Energy flow:Energy flow: energy enters in form of sunlight, converted energy enters in form of sunlight, converted to chemical energy by autotrophs (producers), passed to to chemical energy by autotrophs (producers), passed to heterotrophs (consumers) in food compounds & dissipated heterotrophs (consumers) in food compounds & dissipated (lost) as heat.(lost) as heat.a.) Energy cannot be created or destroyed – just a.) Energy cannot be created or destroyed – just transformed.transformed.b.) Energy conversions are not completely efficient.b.) Energy conversions are not completely efficient.

Ecosystem Ecology cont’d…Ecosystem Ecology cont’d…2.) 2.) Chemical cyclingChemical cycling: Elements such as C & N : Elements such as C & N

are cycled among abiotic & biotic ecosystem are cycled among abiotic & biotic ecosystem components.components.

a.) An atom of carbon moves from trophic level a.) An atom of carbon moves from trophic level to trophic level and eventually to decomposers & to trophic level and eventually to decomposers & then back into the food chain through producers then back into the food chain through producers over and over again.over and over again.

Distinctions b/w energy & matterDistinctions b/w energy & matter::Ecosystems require a constant influx of energy Ecosystems require a constant influx of energy b/c it is not recycled. Elements (matter) are b/c it is not recycled. Elements (matter) are cycled within ecosystems.cycled within ecosystems.

Ecosystem Ecology cont’d…Ecosystem Ecology cont’d…33.) .) Trophic relationshipsTrophic relationships

aa.) .) Primary producersPrimary producers: autotrophs that support all other trophic levels: autotrophs that support all other trophic levels

b.) b.) Primary consumersPrimary consumers: herbivores – eat plants/primary producers: herbivores – eat plants/primary producers

c.) c.) Secondary consumersSecondary consumers: carnivores that eat herbivores: carnivores that eat herbivores

d.) d.) Tertiary consumers:Tertiary consumers: carnivores that eat other carnivores/secondary carnivores that eat other carnivores/secondary

Ecosystem Ecology cont’d…Ecosystem Ecology cont’d…e.) Detritovores/decomposers: consumers that get their e.) Detritovores/decomposers: consumers that get their energy from detritus: nonliving organic material such as energy from detritus: nonliving organic material such as the remains of dead organisms, feces, fallen leaves, etc.the remains of dead organisms, feces, fallen leaves, etc.*Super Important!**Super Important!*

Concept CheckConcept Check

1.) Why is the transfer of energy in an 1.) Why is the transfer of energy in an ecosystem referred to as energy flow, not ecosystem referred to as energy flow, not energy cycling?energy cycling?

2.) Predict what would happen to an 2.) Predict what would happen to an ecosystem if there were no detritovores.ecosystem if there were no detritovores.

Production in EcosystemsProduction in Ecosystems

1.) 1.) Primary productionPrimary production:: the amount of the amount of light energy converted to chemical light energy converted to chemical energy (organic compounds) during a energy (organic compounds) during a given time period.given time period.

a.) This sets the “spending limit” for the a.) This sets the “spending limit” for the “energy budget” of an entire ecosystem.“energy budget” of an entire ecosystem.


b.) Of the visible light that reaches b.) Of the visible light that reaches producers, about 1-2% is converted to producers, about 1-2% is converted to chemical energy through photosynthesischemical energy through photosynthesis

c.) That’s enough though to create 170 c.) That’s enough though to create 170 billion tons of organic material/year!billion tons of organic material/year!

Production in EcosystemsProduction in Ecosystems2.) 2.) Gross Primary Production (GPP):Gross Primary Production (GPP): the total the total

primary production in an ecosystem.primary production in an ecosystem.

a.) Not all of this is stored as organic material in a.) Not all of this is stored as organic material in producers b/c the producers have to use some producers b/c the producers have to use some as fuel for their cellular respiration.as fuel for their cellular respiration.

3.) 3.) Net Primary Production (NPP):Net Primary Production (NPP): equals GPP equals GPP minus the energy used by primary producers for minus the energy used by primary producers for respiration (R). respiration (R).

a.) This is an important measurement – reflects a.) This is an important measurement – reflects what is available to consumers!what is available to consumers!


b.) Can be expressed as energy per unit b.) Can be expressed as energy per unit area per unit time (J/marea per unit time (J/m22/yr)/yr)

c.) Can also be expressed as biomass c.) Can also be expressed as biomass (weight) of vegetation (weight) of vegetation addedadded to ecosystem to ecosystem per unit area per unit time (g/mper unit area per unit time (g/m22/yr)/yr)

d.) NPP varies from one ecosystem to the d.) NPP varies from one ecosystem to the nextnext


i.) Tropical rain forests, coral reefs i.) Tropical rain forests, coral reefs have have high NPP.high NPP.

ii.) How much each ecosystem ii.) How much each ecosystem contributes to GLOBAL NPP depends contributes to GLOBAL NPP depends on how big it is. Even though per unit on how big it is. Even though per unit area the open ocean has a low NPP, area the open ocean has a low NPP, b/c it is so big it contributes more NPP b/c it is so big it contributes more NPP than any other ecosystem.than any other ecosystem.


Primary Production in Aquatic Primary Production in Aquatic EcosystemsEcosystems1.) Primary production in aquatic ecosystems is limited not 1.) Primary production in aquatic ecosystems is limited not

only by light availability/penetration but also by nutrient only by light availability/penetration but also by nutrient availability.availability.

a.) a.) Limiting nutrient:Limiting nutrient: the element that must be added the element that must be added in order for production to increase in a certain area.in order for production to increase in a certain area.

i.) N and P are most often the limiting nutrients in i.) N and P are most often the limiting nutrients in marine ecosystems. Fe can also be a limiting marine ecosystems. Fe can also be a limiting

nutrient.nutrient.

ii.) Adding limiting nutrients typically causes the ii.) Adding limiting nutrients typically causes the pop pop of cyanobacteria to explode. These bacteria “fix” of cyanobacteria to explode. These bacteria “fix” N N making it available to all other phytoplankton making it available to all other phytoplankton whose whose pop then also explodes.pop then also explodes.

Primary Production in Aquatic Primary Production in Aquatic EcosystemsEcosystems

b.) Practical implications:b.) Practical implications:

i.) When sewage and/or fertilizer i.) When sewage and/or fertilizer (containing N (containing N & P) from fields runs off into & P) from fields runs off into freshwater lakes & freshwater lakes & rivers, it can cause an rivers, it can cause an explosion of explosion of cyanobacteria which is called cyanobacteria which is called eutrophication eutrophication or cultural eutrophication.or cultural eutrophication.

ii.) This can severely disrupt an ecosystemii.) This can severely disrupt an ecosystem

Primary Production in Terrestrial and Wetland EcosystemsPrimary Production in Terrestrial and Wetland Ecosystems1.) Temperature and moisture are the key factors controlling 1.) Temperature and moisture are the key factors controlling

primary production in terrestrial ecosystems.primary production in terrestrial ecosystems.

a.) Warm, wet tropical rainforest = high productivity. a.) Warm, wet tropical rainforest = high productivity. Deserts & tundra = low productivity. Intermediate is Deserts & tundra = low productivity. Intermediate is temperate forests & grasslands.temperate forests & grasslands.

b.) b.) Actual evapotranspiration:Actual evapotranspiration: the annual amount of the annual amount of water transpired by plants & evaporated from a landscape.water transpired by plants & evaporated from a landscape.

i.) i.) Transpiration:Transpiration: water loss from plants through pores in water loss from plants through pores in leaves called stomata.leaves called stomata.

c.) Actual evapotranspiration increases with the amount of c.) Actual evapotranspiration increases with the amount of precipitation in a region & the amount of solar energy precipitation in a region & the amount of solar energy available that drives evaporation & transpiration. So, available that drives evaporation & transpiration. So, tropical rain forests have HIGH evapotranspiration & high tropical rain forests have HIGH evapotranspiration & high productivity.productivity.


1.) Why is only a small portion of the solar 1.) Why is only a small portion of the solar energy that strikes Earth’s atmosphere energy that strikes Earth’s atmosphere stored by primary producers?stored by primary producers?

2.) How could ecologists experimentally 2.) How could ecologists experimentally determine the nutrient limiting primary determine the nutrient limiting primary production in an ecosystem?production in an ecosystem?

Concept Check con’td…Concept Check con’td…

3.) Why does the open ocean account for 3.) Why does the open ocean account for almost 25% of Earth’s primary production almost 25% of Earth’s primary production despite its relatively low rate of primary despite its relatively low rate of primary production?production?

4.) Why is an ecosystem’s net primary 4.) Why is an ecosystem’s net primary production lower than its gross primary production lower than its gross primary production?production?

Energy Transfer Between Trophic Energy Transfer Between Trophic LevelsLevels

1.) 1.) Secondary Secondary ProductionProduction: the : the amount of chemical amount of chemical energy in consumers’ energy in consumers’ food that is converted food that is converted to their own new to their own new biomass during a given biomass during a given time period.time period.

Energy Transfer Between Trophic Energy Transfer Between Trophic LevelsLevels2.) 2.) Production efficiency:Production efficiency: the fraction of energy stored in the fraction of energy stored in

food that is not used for respiration.food that is not used for respiration.

a.) Production eff. = a.) Production eff. = Net secondary productionNet secondary production Assimilation of primary prod.Assimilation of primary prod.

i.) Net secondary production = the energy stored in i.) Net secondary production = the energy stored in biomass (represented by growth/reproduction).biomass (represented by growth/reproduction).

ii.) Assimilation = total energy taken in &used for ii.) Assimilation = total energy taken in &used for growth/reproduction & respiration.growth/reproduction & respiration.

Energy Transfer Between Trophic Energy Transfer Between Trophic LevelsLevelsb.) For the caterpillar, the b.) For the caterpillar, the production efficiency is production efficiency is 33%.33%.

i.) Of the 100 J of i.) Of the 100 J of energy actually taken energy actually taken in, 67 J are used for in, 67 J are used for cell resp and only 33 cell resp and only 33 J are used for J are used for growth/reproduction. growth/reproduction. (Don’t count the (Don’t count the energy that goes to energy that goes to feces…)feces…)

Energy Transfer Between Trophic Energy Transfer Between Trophic LevelsLevels

c.) Birds & mammals typically have a production c.) Birds & mammals typically have a production efficiency of only 1-3% because they use so much efficiency of only 1-3% because they use so much energy to maintain a constant body temperature.energy to maintain a constant body temperature.

i.) Endotherms: maintain constant body i.) Endotherms: maintain constant body temp.temp.

d.) Fish have a production efficiency around 10% and d.) Fish have a production efficiency around 10% and insects around 40%.insects around 40%.

ii.) Ectotherms: body temp fluctuates with temp ii.) Ectotherms: body temp fluctuates with temp of of environmentenvironment

Trophic EfficiencyTrophic EfficiencyDefinition: the % of production transferred from one trophic Definition: the % of production transferred from one trophic

level to the next. level to the next.

1.) Takes into account the energy lost through respiration & 1.) Takes into account the energy lost through respiration & contained in feces & the energy in a lower trophic level that contained in feces & the energy in a lower trophic level that is not consumed at the next trophic level.is not consumed at the next trophic level.2.) Ranges from 5-20%.2.) Ranges from 5-20%.

a.) This means that 80-95% of the energy available at a.) This means that 80-95% of the energy available at one trophic level is not transferred to the next.one trophic level is not transferred to the next.

b.) The loss is multiplied at each step of a food chain:b.) The loss is multiplied at each step of a food chain:

i.) If 10% of energy is transferred from primary i.) If 10% of energy is transferred from primary prod to prod to primary consumers and 10% of that primary consumers and 10% of that energy is energy is transferred To secondary consumers, transferred To secondary consumers, then really only 1% then really only 1% of NPP is available to of NPP is available to secondary consumers.secondary consumers.

Trophic EfficiencyTrophic Efficiency

c.) So, about 0.1% of energy fixed by c.) So, about 0.1% of energy fixed by photosynthesis can flow to a tertiary photosynthesis can flow to a tertiary consumer.consumer.

i.) This loss of energy probably i.) This loss of energy probably explains why most food webs are explains why most food webs are only only about 4 – 5 trophic levels about 4 – 5 trophic levels long.long.

Pyramid of ProductionPyramid of Production

1.) Used to 1.) Used to represent the represent the loss of energy loss of energy at each at each trophic level.trophic level.

2.) Size of 2.) Size of each block is each block is proportional proportional to the net to the net production of production of trophic level.trophic level.

Pyramid of BiomassPyramid of Biomass1.) Each tier of pyramid represents the standing 1.) Each tier of pyramid represents the standing

crop biomass of one trophic level.crop biomass of one trophic level.

a.) a.) Standing cropStanding crop: the total dry weight of all : the total dry weight of all organisms.organisms.

2.) Most biomass pyramids narrow from primary 2.) Most biomass pyramids narrow from primary producers to top level consumers because producers to top level consumers because energy transfers are so inefficient.energy transfers are so inefficient.

a.) Some aquatic ecosystems are inverted b/c a.) Some aquatic ecosystems are inverted b/c phytoplankton grow, reproduce & are eaten so phytoplankton grow, reproduce & are eaten so quickly that they never build a huge biomass.quickly that they never build a huge biomass.

Most biomass pyramids are similar to example (a) above. Some aquatic ecosystems may resemble example (b).

Pyramid of NumbersPyramid of Numbers1.) Represents the number of individual organisms 1.) Represents the number of individual organisms

present in each trophic level.present in each trophic level.

a.) Narrows toward top b/c top consumers a.) Narrows toward top b/c top consumers tend to be large and fewer in numbers.tend to be large and fewer in numbers.

Eat less meat & eat more plants!Eat less meat & eat more plants!The way energy flows through an ecosystem implies The way energy flows through an ecosystem implies

a lot about how we should feed our population…a lot about how we should feed our population…

1.) Eating meat is an inefficient way to tap into 1.) Eating meat is an inefficient way to tap into photosynthetic production.photosynthetic production.

2.) You obtain far more calories by eating a certain 2.) You obtain far more calories by eating a certain amount of grain directly as a primary consumer amount of grain directly as a primary consumer than by processing that same amount of grain than by processing that same amount of grain through another trophic level and eating meat from through another trophic level and eating meat from grain fed animals.grain fed animals.

3.) We could feed MANY more people & use a lot 3.) We could feed MANY more people & use a lot less land if we all fed as primary consumers – i.e. if less land if we all fed as primary consumers – i.e. if we were all vegetarians.we were all vegetarians.

The Green World HypothesisThe Green World HypothesisIf so many primary consumers feed on the If so many primary consumers feed on the

producers then why are ecosystems still producers then why are ecosystems still so green?so green?

1.) According to the GWH terrestrial 1.) According to the GWH terrestrial herbivores consume relatively little plant herbivores consume relatively little plant biomass b/c they are held in check by biomass b/c they are held in check by predators, parasites, disease, etc.predators, parasites, disease, etc.

Concept CheckConcept Check1.) If an insect that eats plant seeds containing 1.) If an insect that eats plant seeds containing

100 J of energy uses 30 J of that energy for 100 J of energy uses 30 J of that energy for respiration and excretes 50 J in its feces, what respiration and excretes 50 J in its feces, what is the insect’s net secondary production? What is the insect’s net secondary production? What is its production efficiency?is its production efficiency?

a.) Net secondary = a.) Net secondary = 20 J 20 J = 20% = 20%100J100J

b.) Prod. Efficiency = b.) Prod. Efficiency = 20 J20 J = 40% = 40% 50 J50 J


Why does the production pyramid have the Why does the production pyramid have the same general shape as the biomass same general shape as the biomass pyramid in most ecosystems? Under pyramid in most ecosystems? Under what circumstances might the shapes of what circumstances might the shapes of the two pyramids differ?the two pyramids differ?

Nutrient CyclingNutrient Cycling

While energy flows While energy flows THROUGH ecosystems, THROUGH ecosystems, nutrients can cycle within nutrients can cycle within them.them.

Nutrient cycles are called Nutrient cycles are called biogeochemical cyclesbiogeochemical cycles because these circuits because these circuits involve both biotic & involve both biotic & abiotic components.abiotic components.

The Water CycleThe Water Cycle

The Carbon CycleThe Carbon Cycle

The Nitrogen CycleThe Nitrogen Cycle*Important! Most N is in atmosphere. Only becomes available to plants via nitrogen fixation which is carried out by special bacteria. We get all our nitrogen by eating plants or animals that eat plants.

The Phosphorous CycleThe Phosphorous Cycle

Phosphate is absorbed by plants – that’s how we get it. Again, from eating plants or eating animals that eat plants.

Why do we care about C, N Why do we care about C, N & P?& P?

1.) Carbon: the basis of ALL organic 1.) Carbon: the basis of ALL organic molecules (all the molecules that we are molecules (all the molecules that we are made of).made of).

2.) Nitrogen: component of amino acids, 2.) Nitrogen: component of amino acids, proteins & nucleic acids.proteins & nucleic acids.

3.) Phosphorous: component of nucleic 3.) Phosphorous: component of nucleic acids, phospholipids & ATP.acids, phospholipids & ATP.

Too many humans = Disruption of Too many humans = Disruption of Biogeochemical cycles!Biogeochemical cycles!

Nutrient EnrichmentNutrient Enrichment1.) Human activities often remove nutrients from one 1.) Human activities often remove nutrients from one

ecosystem & deposit them in another.ecosystem & deposit them in another.

a.) Agriculture: nutrients in farm soil (maybe artificial – a.) Agriculture: nutrients in farm soil (maybe artificial – fertilizers) run off into lakes or streams = fertilizers) run off into lakes or streams = cultural cultural eutrophication.eutrophication.

i.) Cultural eutrophication disrupts fish i.) Cultural eutrophication disrupts fish populations populations – often wiping them out. All the excess – often wiping them out. All the excess plants/algae die and then decompose. The plants/algae die and then decompose. The decomposers use up all oxygen – kills fish.decomposers use up all oxygen – kills fish.

Acid PrecipitationAcid Precipitation1.) Burning fossil fuels releases sulfur & nitrogen oxide.1.) Burning fossil fuels releases sulfur & nitrogen oxide.

a.) Reacts with water in atmosphere forming sulfuric & a.) Reacts with water in atmosphere forming sulfuric & nitric acid – then falls to earth as acid precipitation.nitric acid – then falls to earth as acid precipitation.

2.) Lowers aquatic ecosystem pH & disrupts soil 2.) Lowers aquatic ecosystem pH & disrupts soil chemistry.chemistry.

3.) Industry in one area usually produces acid 3.) Industry in one area usually produces acid precipitation that falls in another.precipitation that falls in another.

Toxins in EnvironmentToxins in Environment1.) We release an immense amount of synthetic 1.) We release an immense amount of synthetic

chemicals into ecosystems – many of which are chemicals into ecosystems – many of which are toxic (we don’t know or we don’t care).toxic (we don’t know or we don’t care).

2.) Organisms can metabolize & excrete some but 2.) Organisms can metabolize & excrete some but others accumulate in organisms’ tissues.others accumulate in organisms’ tissues.

3.) Toxins that accumulate become more and 3.) Toxins that accumulate become more and more concentrated at higher and higher trophic more concentrated at higher and higher trophic levels = levels = biological magnification.biological magnification.

a.) Occurs b/c the biomass at any given trophic a.) Occurs b/c the biomass at any given trophic level is produced from a much larger biomass level is produced from a much larger biomass ingested from the level below.ingested from the level below.

Biological Magnification of DDTBiological Magnification of DDT

DDT used to control DDT used to control mosquitoes.mosquitoes.

DDT softened bird DDT softened bird eggshells – shells eggshells – shells broke = huge decline broke = huge decline in reproduction.in reproduction.

Rachel Carson’s Rachel Carson’s Silent Silent SpringSpring drew attention drew attention to problem.to problem.

http://www.storyofstuff.com/http://www.storyofstuff.com/

http://www.chrisjordan.com/http://www.chrisjordan.com/

http://www.storyofstuff.com/

http://www.chrisjordan.com/

Atmospheric Carbon DioxideAtmospheric Carbon Dioxide1.) Atmospheric levels of carbon dioxide are on the rise.1.) Atmospheric levels of carbon dioxide are on the rise.

2.) The Greenhouse Effect & Global Warming2.) The Greenhouse Effect & Global Warming

a.) Much of the solar radiation that strikes Earth is a.) Much of the solar radiation that strikes Earth is reflected back into space.reflected back into space.

b.) However, gases in Earth’s atmosphere such as b.) However, gases in Earth’s atmosphere such as carbon dioxide and water vapor absorb much of the carbon dioxide and water vapor absorb much of the reflected radiation – this warms the Earth = very reflected radiation – this warms the Earth = very important.important.

i.) If not for this i.) If not for this greenhouse effectgreenhouse effect the average the average temperature on Earth would be below zero!temperature on Earth would be below zero!

Atmospheric Carbon DioxideAtmospheric Carbon Dioxide

c.) There has been a huge increase in the c.) There has been a huge increase in the concentration of atmospheric carbon concentration of atmospheric carbon

dioxide dioxide (due to human burning of fossil fuels (due to human burning of fossil fuels mainly).mainly).

d.) Increase carbon dioxide concentration d.) Increase carbon dioxide concentration = = increase in global temperature = melting of increase in global temperature = melting of

polar ice caps (?), flooding of coastal polar ice caps (?), flooding of coastal areas areas (?), changes in global climate (?), changes in global climate patterns (?) patterns (?) …yikes.…yikes.

Depletion of Atmospheric OzoneDepletion of Atmospheric Ozone1.) A layer of ozone molecules 1.) A layer of ozone molecules

(O(O33) protects Earth from ) protects Earth from much of the damaging UV much of the damaging UV radiation from the sun by radiation from the sun by absorbing it.absorbing it.

2.) Ozone layer has been 2.) Ozone layer has been thinning!thinning!

a.) Accumulation of CFCs a.) Accumulation of CFCs (chemicals found in (chemicals found in refrigerants, aerosol cans) refrigerants, aerosol cans) react with ozone molecules & react with ozone molecules & change it into regular oxygen.change it into regular oxygen.

3.) Many nations no longer 3.) Many nations no longer produce CFCs but “holes” in produce CFCs but “holes” in ozone are still there!ozone are still there!

Concept Check Concept Check

1.) In the face of biological magnification of 1.) In the face of biological magnification of toxins, is it healthier to feed at a lower or toxins, is it healthier to feed at a lower or higher trophic level? Explain.higher trophic level? Explain.

2.) How can clear cutting a forest 2.) How can clear cutting a forest (removing all the trees) damage the (removing all the trees) damage the water quality of nearby lakes?water quality of nearby lakes?

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Chapter 54