AnnouncementsAnnouncements

• Fisheries problem is due now Fisheries problem is due now • No class on WednesdayNo class on Wednesday• Problem set is due in your TA’s box Problem set is due in your TA’s box

by 10am on Wednesday, November by 10am on Wednesday, November 2424thth

Summary from FridaySummary from Friday

• Economics of fishingEconomics of fishing• What causes overfishingWhat causes overfishing• Biological magnificationBiological magnification• AquacultureAquaculture

Two minute quizTwo minute quiz

1)1) With regard to fisheries, how is cost With regard to fisheries, how is cost related to effort? How is effort related to effort? How is effort related to population size? related to population size?

2)2) How can government subsidies lead How can government subsidies lead to overfishing?to overfishing?

3)3) Why are cheap fisheries more likely Why are cheap fisheries more likely to be unsustainable than more to be unsustainable than more expensive fisheries?expensive fisheries?

benefit matches cost at this point

cost

Rat

e of

har

vest

(be

nefit

or

inco

me)

Cos

t

Population SizeK 0

harvest (benefit or income)

Effort 0% 100%

minimum population where fishing is economically viable

Uns

ubsi

dize

d co

st

Government subsidiesmaintain jobs, provide protein, but lead to over- fishing

minimum population where fishing is economically viable

Subsidized cost

Rat

e of

har

vest

(be

nefit

or

inco

me)

Su

bsid

ize

d o

r U

nsu

bsi

diz

ed

cos

t

Population SizeK 0

Effort 0% 100%

benefit matches cost at this point

cost

Expensive fisheryonly profitable when population sizes are large, likely to be sustainable

minimum population where fishing is economically viable

Rat

e of

har

vest

(be

nefit

or

inco

me)

Cos

t

Population SizeK 0

Effort 0% 100%

benefit matches cost at this point

cost

Cheap fisheryprofitable at small population size, likely to be unsustainable

minimum population where fishing is economically viable

Rat

e of

har

vest

(be

nefit

or

inco

me)

Cos

t

Population SizeK 0

Effort 0% 100%

Case Study: Salmon FarmingCase Study: Salmon Farming

• People like salmonPeople like salmon

• Wild populations are threatenedWild populations are threatened

• Farming used as a solution for Farming used as a solution for providing people with the fish they providing people with the fish they want to eatwant to eat

Case Study: Salmon FarmingCase Study: Salmon Farming• problems with salmon farming:problems with salmon farming:

• escapesescapes• interbreeding with wild populationinterbreeding with wild population

• genetic engineeringgenetic engineering

•competing with wild populationscompeting with wild populations

• farmed salmon are fed wild-caught fishfarmed salmon are fed wild-caught fish•3 pounds of wild fish for 1 pound of farmed 3 pounds of wild fish for 1 pound of farmed

salmonsalmon

• pollution from waste and left-over foodpollution from waste and left-over food• disease spreaddisease spread

•high density of fish in cageshigh density of fish in cages

• aestheticsaesthetics

Marine ReservesMarine Reserves• Prime fish are larger and olderPrime fish are larger and older

• Normal fishing removes the largest Normal fishing removes the largest fishfish• eventually all big fish are caughteventually all big fish are caught

•quality of fish goes downquality of fish goes down

•reproductive success of fish goes downreproductive success of fish goes down

• Reserves allow some fish to grow to Reserves allow some fish to grow to maturitymaturity

• Fishing improvesFishing improvesprotected protected

areaareaunprotectedunprotected

areaarea

AgricultureAgriculture

• Costs and BenefitsCosts and Benefits• Ecosystem Dynamics vs. Food Ecosystem Dynamics vs. Food

ProductionProduction• Ecological Problems associated with:Ecological Problems associated with:

• tillagetillage• use of chemical pesticides, herbicides, use of chemical pesticides, herbicides,

etc. etc. • irrigationirrigation

AgricultureAgriculture

• Like fisheries: similar concerns of Like fisheries: similar concerns of balancing yield and sustainabilitybalancing yield and sustainability

• Environmental impacts can be largeEnvironmental impacts can be large• Goal is to maximize productivityGoal is to maximize productivity

plant growth is usually nutrient limited

nutrient supply

yiel

d

AgricultureAgriculture• Benefit from crops = yieldBenefit from crops = yield• Cost goes up with fertilizer Cost goes up with fertilizer

applicationapplication

nutrient supply

yiel

d cheap fertilizer

expe

nsive

ferti

lizer

benefit

Fate of fertilizerFate of fertilizer

• Taken up by plantsTaken up by plants• Leached from the systemLeached from the system

• enters systems downstreamenters systems downstream

• Denitrified and converted into N Denitrified and converted into N gassesgasses

Ecosystem DynamicsEcosystem Dynamics

• A crop field is an ecosystem!A crop field is an ecosystem!• all natural biological processes can all natural biological processes can

occur:occur:•competitioncompetition•herbivoryherbivory•diseasedisease

• why would a farmer care?why would a farmer care?

Ecosystem DynamicsEcosystem Dynamics

• A crop field is an ecosystem!A crop field is an ecosystem!• all natural biological processes can all natural biological processes can

occur:occur:•competitioncompetition•herbivoryherbivory•diseasedisease

• why would a farmer care?why would a farmer care?• achieving peak yield requires that these achieving peak yield requires that these

processes be limitedprocesses be limited

Ecosystem DynamicsEcosystem Dynamics

• Monoculture= one species of plantMonoculture= one species of plant• encourages competition, herbivory, and encourages competition, herbivory, and

diseasedisease• fertilization fertilization enhances growth of all enhances growth of all

plants, but crops are bred to be poor plants, but crops are bred to be poor competitorscompetitors• energy is allocated to the portions that people energy is allocated to the portions that people

eat…not to roots for uptakeeat…not to roots for uptake

• specialist herbivores do well in monoculturespecialist herbivores do well in monoculture• disease can spread easily if all plants are disease can spread easily if all plants are

the same speciesthe same species

Food ProductionFood Production

• The goal of agriculture is to The goal of agriculture is to produce produce foodfood

• Farmers use many techniques to limit Farmers use many techniques to limit competition, herbivory and diseasecompetition, herbivory and disease• tillagetillage• herbicidesherbicides• insecticidesinsecticides• fungicidesfungicides

• These things increase yields, but also These things increase yields, but also have environmental impactshave environmental impacts

TillageTillage• Plowing has been used for thousands of Plowing has been used for thousands of

years years • kill weedskill weeds• prepare the seed bedprepare the seed bed• stimulate nutrient mineralizationstimulate nutrient mineralization

TillageTillage• Plowing is a powerful tool for Plowing is a powerful tool for

maximizing crop productionmaximizing crop production• Drawback:Drawback:

• loose, bare soil is vulnerable to loose, bare soil is vulnerable to erosionerosion by wind and waterby wind and water

What is topsoil?What is topsoil?

• Topsoil is a semi-renewable resourceTopsoil is a semi-renewable resource• A horizonA horizon• Good water retentionGood water retention• Easy root penetrationEasy root penetration• Rich in organic matterRich in organic matter• Can be 50-60 cm thick in prairieCan be 50-60 cm thick in prairie

• Forms on the order of millimeters per Forms on the order of millimeters per yearyear

• About 1/3 has been lost from Midwest About 1/3 has been lost from Midwest since European settlementsince European settlement

AnnouncementsAnnouncements

• This week we will:This week we will:• Finish up AgricultureFinish up Agriculture• Cover ConservationCover Conservation• Go over the midtermGo over the midterm• Review for the finalReview for the final• Fill out evaluationsFill out evaluations• Have a science ethics discussion?Have a science ethics discussion?

Two-minute quizTwo-minute quiz

A. True or false:A. True or false:• A crop field is an ecosystem.A crop field is an ecosystem.• All of the fertilizer applied to a field is All of the fertilizer applied to a field is

taken up by plants and used for taken up by plants and used for growth. growth.

• The “dead zone” in the Gulf of Mexico The “dead zone” in the Gulf of Mexico is primarily caused by overfishing. is primarily caused by overfishing.

B. Name three problems associated with B. Name three problems associated with aquaculture.aquaculture.

Summary from FridaySummary from Friday

• Salmon as an aquaculture case studySalmon as an aquaculture case study• Marine ReservesMarine Reserves• AgricultureAgriculture• Costs and BenefitsCosts and Benefits• Ecosystem Dynamics vs. Food Ecosystem Dynamics vs. Food

ProductionProduction• Ecological Problems associated with:Ecological Problems associated with:

• tillage tillage erosion erosion

What is topsoil?What is topsoil?

• Topsoil is a semi-renewable resourceTopsoil is a semi-renewable resource• A horizonA horizon• Good water retentionGood water retention• Easy root penetrationEasy root penetration• Rich in organic matterRich in organic matter• Can be 50-60 cm thick in prairieCan be 50-60 cm thick in prairie

• Forms on the order of millimeters per Forms on the order of millimeters per yearyear

• About 1/3 has been lost from Midwest About 1/3 has been lost from Midwest since European settlementsince European settlement

How much is topsoil worth?How much is topsoil worth?

• Assume a loss of Assume a loss of 1 inch of topsoil over 1 acre1 inch of topsoil over 1 acre• 1” = 2.54 cm1” = 2.54 cm• 1 m1 m2 2 = 10,000 cm= 10,000 cm22

• 1 acre = 4070 m1 acre = 4070 m22

• bulk density of topsoil = 1.4 g/cmbulk density of topsoil = 1.4 g/cm33

• 1” over 1 acre = 1” over 1 acre = • 103,378,000 cm103,378,000 cm33 = 144,729,200 g = 145 Tons = 144,729,200 g = 145 Tons

• Topsoil costs $20 per yardTopsoil costs $20 per yard33 = 0.85 Tons = 0.85 Tons• 145 Tons equals a 145 Tons equals a cash loss of $3,412.00cash loss of $3,412.00

• A 50 cm thick A horizon would be worth $67,000 per A 50 cm thick A horizon would be worth $67,000 per acre.acre.

Can topsoil be replaced?Can topsoil be replaced?

• ““Topsoil” from a nursery is usually Topsoil” from a nursery is usually compost + subsoil (B horizon)compost + subsoil (B horizon)• where does the compost come from?where does the compost come from?

• Would dredging the Mississippi Delta Would dredging the Mississippi Delta work?work?• A horizon has a mix of sand, silt, and clayA horizon has a mix of sand, silt, and clay• river or wind transports particles at different river or wind transports particles at different

ratesrates• how to put them back together?how to put them back together?

• how would you pay for dredging and how would you pay for dredging and transporttransport

• what about salinity?what about salinity?

Off-site costs of erosionOff-site costs of erosion

• SedimentationSedimentation• fills up reservoirs, rivers, and lakesfills up reservoirs, rivers, and lakes• 4 billion tons/year deposited in the U.S.4 billion tons/year deposited in the U.S.

• Effects:Effects:• loss of water storagesloss of water storages• loss of fishing groundsloss of fishing grounds• loss of wetlands and estuariesloss of wetlands and estuaries• loss of offshore reefsloss of offshore reefs

How to limit erosionHow to limit erosion

• Contour plowing: across a slopeContour plowing: across a slope• creates lots of micro-damscreates lots of micro-dams

• Cover-cropping: Cover-cropping: • plant something during the non-growing plant something during the non-growing

season to keep soil from erodingseason to keep soil from eroding

• No-till agriculture: don’t plow at all No-till agriculture: don’t plow at all • seeds are drilled directly into soilseeds are drilled directly into soil• problems?problems?

Use of Pesticides/HerbicidesUse of Pesticides/Herbicides

• CostCost• expensive to buy and disperseexpensive to buy and disperse

• HealthHealth• many are toxic to humansmany are toxic to humans

• Ecological EffectsEcological Effects• when washed downstream, can affect when washed downstream, can affect

other ecosystemsother ecosystems• can select for resistant strains of pestscan select for resistant strains of pests

IrrigationIrrigation• Crops grow well in warm climatesCrops grow well in warm climates

• sunlightsunlight• appropriate temperaturesappropriate temperatures• good soilgood soil

• Water often limits growth Water often limits growth irrigation irrigation

SalinizationSalinization• Common result of irrigationCommon result of irrigation• Salts precipitate out of solution in soilSalts precipitate out of solution in soil• Occurs when:Occurs when:

• climate is warm and dryclimate is warm and dry• water table is highwater table is high• salts are presentsalts are present

• Problem: too much salt kills plantsProblem: too much salt kills plants• primary cause: plants are unable to take primary cause: plants are unable to take

up waterup water• secondary cause: toxicity of Nasecondary cause: toxicity of Na++ and Cl and Cl--

Mechanism of SalinizationMechanism of Salinization

• Irrigation: most water contains a Irrigation: most water contains a small amount of saltsmall amount of salt• accumulation over timeaccumulation over time

• Surface soils dry up, and water from Surface soils dry up, and water from deeper soil moves upwardsdeeper soil moves upwards

• Evaporation: leaves salts on surfaceEvaporation: leaves salts on surface

Food ProductionFood Production

• How can farmers reduce environmental How can farmers reduce environmental impacts while still keeping yields high?impacts while still keeping yields high?• limit monoculturelimit monoculture

• intercrop or rotate cropsintercrop or rotate crops

• plant a variety of genotypesplant a variety of genotypes• currently, some fields have a single clone of currently, some fields have a single clone of

corncorn

• control pests with natural predatorscontrol pests with natural predators• use ladybugs to control aphidsuse ladybugs to control aphids

• use chemicals only when necessaryuse chemicals only when necessary

ConservationConservation

• Long term management plans can be Long term management plans can be used to conserve resourcesused to conserve resources

• Resource Management Resource Management can include:can include:• management of materialsmanagement of materials• management of plants or animals that management of plants or animals that

are used for food, fiber, or other are used for food, fiber, or other purposespurposes

Resource managementResource managementThere are 3 different classes of resources:There are 3 different classes of resources:

• RenewableRenewable• airair

• Semi-renewable: Semi-renewable: renewable if not over-renewable if not over-harvestedharvested• waterwater• soilsoil• fish populationsfish populations

• Non-renewableNon-renewable• fossil fuelsfossil fuels• certain mineralscertain minerals

Resource managementResource management

• Biological resources are Biological resources are fragile!fragile!

• Populations can easily be over-Populations can easily be over-harvestedharvested• fisheries are often over-fishedfisheries are often over-fished

ConservationConservation

• keystone specieskeystone species• ““flagship species”flagship species”• long-term land protection: reserveslong-term land protection: reserves

single-species management

AnnouncementsAnnouncements

• Professor Levine’s announcementProfessor Levine’s announcement• This week we will:This week we will:

• Finish up ConservationFinish up Conservation• Go over the midtermGo over the midterm• Review for the finalReview for the final• Fill out evaluationsFill out evaluations• Have a science ethics discussion?Have a science ethics discussion?

Two-minute quizTwo-minute quiz

A. True or false:A. True or false:• A flagship species must be a A flagship species must be a

keystone species.keystone species.• Coal is a renewable resource.Coal is a renewable resource.• Cover cropping can reduce erosion Cover cropping can reduce erosion

during the non-growing season.during the non-growing season.

B. Name two problems caused by B. Name two problems caused by sedimentation.sedimentation.

Summary from MondaySummary from Monday

• Replacement of TopsoilReplacement of Topsoil• costcost• feasibilityfeasibility

• SedimentationSedimentation• Limiting ErosionLimiting Erosion• Pesticides and HerbicidesPesticides and Herbicides• Irrigation and SalinizationIrrigation and Salinization• Resource Management and Resource Management and

ConservationConservation

Designing a reserveDesigning a reserve• Shape and SizeShape and Size

• determine minimum viable area (MVA) determine minimum viable area (MVA) needed for each populationneeded for each population• estimates of energy use by trophic levelestimates of energy use by trophic level• territorialityterritoriality• landscape structurelandscape structure

• one large or several small?one large or several small?

A larger area can support more animals

Edge effectEdge effect

• circular reserves have less edgecircular reserves have less edge• edge effects include gradients in:edge effects include gradients in:

• lightlight• moisturemoisture• windwind• noisenoise• pollutionpollution

• outside may be unprotectedoutside may be unprotected

Shape determines edge effect

One largeOne large oror several small? several small?

• minimize edge minimize edge effectseffects

• more complete food more complete food chainschains

• lower risk of lower risk of inbreedinginbreeding

BUT…BUT…• at risk from at risk from

environmental environmental disaster and diseasedisaster and disease

• may be easier to may be easier to accomplish accomplish politicallypolitically

• can create can create corridors so than corridors so than animals can animals can interbreedinterbreed

= limited protection

= full protection