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Announcements

• Extra credit screenplays due today• First exam on Feb 2nd in class• Study guide for midterm 1 posted on

under “Lecture Notes” – Watch for updates

• Note taker• Today: Critical thinking assignment

and more on ecosystems

Critical-thinking assignmentWhich reading presented a less-biased view?Which reading did the better job of

supporting its facts?

Does fracking contaminate groundwater? Does fracking increase or decrease GHG emissions?

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HowarthIngraffea

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Critical-thinking assignmentShould we frack?

Opinion before readings Opinion after readings

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Earthquakes in Oklahoma (>M3)

Geophysical models implicate deep-well injection of fracking fluidsas the cause of the Oklahoma earthquakes

Source: Oklahoma Geological Survey

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By the end of class today…

• Understand the fundamental functions of ecosystems

• Recognize how energy is produced and transferred through food webs

• Relate ecosystem processes to the global cycling of carbon and nitrogen

• If we have time…understand importance of ecological and evolutionary processes that shape ecosystems.

• UV protection• Air purification• Flood mitigation• Drought mitigation• Pest control• Water purification• Waste decomposition

• Soil formation• Seed dispersal• Aesthetic, cultural• Recreation• Climate stabilization• Erosion protection• Nutrient cycling

Ecosystem services

Primary functions: Energy capture and distributionNutrient cycling

Ecosystem Functions

• Photosynthesis (plants)(light)

6CO2 + 6H2O → C6H12O6 + 6O2 (requires energy)carbon water glucose oxygendioxide

• Respiration (plants, animals, bacteria,…)C6H12O6 + 6O2 → 6CO2 + 6H2O (oxidation releases

energy)

Demo

Ecosystem Function: Production and respiration

6CO2 + 6H2O + nutrients, light ↔ C6H12O6 + 6O2

nonliving ↔ living inorganic compounds ↔ organic compounds

CO2 and nutrients ↔ biomass kinetic energy ↔ potential energy

(energy of motion) (stored energy)

Materials are recycled, energy moves through the system

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Ecosystem Function: Food Chains

• Food-chain trophic levels– Producers– Primary consumers– Secondary consumers– Tertiary consumers

Ecosystem Function: Energy transfer among trophic levels

• Only about 10% of E transferred to the next level

• 90% lost to respiration

• This results in the biomass “pyramid”

Ecosystem Function: Food Webs

• Simple food chains are rare in nature

• Many species of producers and consumers create complex food webs

Summary of Ecosystem Functions

• Energy flow

• Nutrient flow

• (Energy + Nutrients)

Sustainability lesson:Energy from the sunNutrients recycled

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Global biogeochemical cycles

• Ecosystem processes control the cycling of:– Carbon– Oxygen– Nitrogen– Phosphorus– Sulfur– Metals (such as iron, manganese, etc.)

• Human activities modify these cycles

Carbon Cycle

• CO2 → organic carbon by photosynthesis• Organic C → CO2 by respiration• CO2 dissolved in seawater → organism

shells of calcium carbonate (CaCO3)• Dissolution of CaCO3 → dissolved CO2

• Organic C and CaCO3 buried in marine sediments (long-term carbon sink)

• This lost CO2 replaced by volcanism• Fossil fuels and vegetation burning → CO2

EssentialGlobal CarbonCycle

Arrows and purple numbers: Fluxes in 1015 g C/yBlack numbers: Storage pools in 1015 g C

Rivers

Changes in atmospheric CO2

CO2 data from http://scrippsco2.ucsd.edu

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Nitrogen Cycle

• Nitrogen fixation: Bacteria convert nitrogen gas into amino acids (N2 → biomass (NH3-acid))

• Nitrogen uptake: Plants take up N (NH3 and NO3-)

during photosynthesis, moves up food chain• Ammonification: Organism wastes release ammonia

(NH3, NH4+ )

• Nitrification: Bacteria convert ammonium to nitrate (NH4

+→ NO2-→ NO3

-)• Denitrification: Bacteria convert nitrate to nitrogen gas

(NO3-→ N2 or NH4

+ + NO2− → N2 + 2H2O)

• Fertilizer production and use: N2 → NH3 + NO3-

Simplified Nitrogen Cycle

N2 in atmosphere

Nitrogen fixation

organicmatter(NH3)

NH4+

Ammonification

NO2+

NO3+

Nitrification

Photosynthesis

Denitrification(anaerobicconditions)

N a component of: proteins

DNAchlorophyll

etc. N as a nutrient

N mostly unavailable

Available N

Nitrogen and “dead zones”

From Diaz and Rosenberg, “Spreading dead zones and consequences for marine ecosystems”. Science, 15 August 2008

Ecosystem function summary

• Ecosystems sustain life• Many functions

– Primary: Energy capture and transferNutrient recycling

• Food webs transfer energy, nutrients• Global biogeochemical cycles• Humans activity changes ecosystem function

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‘‘All animals are equal, but some animals are more equal than others.’’

George Orwell (1945)

Biodiversity

• Variety of life (species, genes, functional groups) in a particular area

• Biodiversity affects ecosystem function– Productivity– Stability– Resilience– Invasion resistance

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Otters eat many invertebrates (especially sea urchins). Areas with otters had fewer prey species than areas without otters.

Data from R.G. Kvitek, D.H. Shull, et al., 1989, Marine Mammal Science

Sea Otters

Present Absent

Few sea urchins Many sea urchins

Algae → Sea urchins → Sea otters These data indicate top-down control

Bladder kelp Bull kelpMacrocystic integrifolia Nereocystis luetkeanaPerennial, fast growing, preferred food Annual, slower growing, not as tasty

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Ecological processes in ecosystems

• Processes affecting organism distributions and species diversity in ecosystems– Predation– Competition– Disturbance– Positive interactions (facilitation, symbioses)

• Humans are wildlife competitors, predators, disturbers and facilitators

Keystone Species

• Definition: a species whose effect on an ecosystem is disproportionately large relative to its abundance

• Examples:– The ochre star fish (Pisaster ochraceus) – Crown-of-thorns starfish (Acanthaster planca)– The alewife (a small fish, Alosa sp.)– African elephants– Sea otter

Effects of Pisaster predation

Limit mussel distribution to upper intertidal regionIncrease species diversity by limiting competition by mussels(Intermediate disturbance hypothesis)

Sea star wasting disease

Presence of wasting disease

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From Hickman et al. 2003. Animal Diversity

Evolution and ecosystems

Present

500 million y

Evolution and ecosystems• Species composition of ecosystems are constantly

changing

• Time scales of change– Ecological time vs. Evolutionary time

• Extinction– Average duration of species in the fossil record is

about 1 million years (range: ~1 to ~10 million years). – Human activity is a strong selective force– What kinds of animals are we selecting for?– How does the rate of extinction today compare with

rates in the past?

Rates of Extinction• Given average durations of species, expect ~ 10 to 50 species per

year to become extinct

• In tropical rain forests, it is estimated that more than 20,000 endemic species are lost each year to deforestation

• For mammals (~ 5000 species), a duration of 1 MY indicates one species would become extinct about every 200 years.

• In last 400 years, ~ 90 species have become extinct (45x expected) and about 170 are critically endangered.

• We seem to be in the middle of a mass extinction. What kinds of species will survive?