Announcements

September 25, 2006

One exam down, two to go…(unless you need to take the final).

Should have results in this week.

Communities and Ecosystems

Lecture Objectives:

2. Learn to classify organisms based on their position in the food chain/food web

1. Differentiate between a community and an ecosystem

• Community — Assemblage of all interacting populations of organisms in an area.

• Ecosystem — System of all interacting organisms, including their non-living surroundings. – biotic and abiotic

EcosystemCommunity

PopulationIndividual

Can classify organisms by how they interact with one another

Predator versus prey

Host versus parasite

But can also classify organisms by how theyobtain nutrients

Trophic Pyramid

Atom — Fundamental unit of matter. 92 kinds of atoms (elements) in nature (plus several others that have been synthesized)

The elements that we care most about are:

Carbon - C

Nitrogen - N

Phosphorus - P

Oxygen - O

Hydrogen - H

Molecules — Atoms bonded together into stable units.

Water molecule: H2O

Roles of Organisms in the trophic pyramid

Producers — Organisms able to use sources of energy to make complex organic molecules from simple inorganic molecules in the environment.

Organic – biological—contains multiple carbon atoms (e.g., sugars)

Inorganic – non biological

Photosynthesis:

6CO2 + 6H2O C6H12O6 + 6O2

Process used by plants to convert inorganic material into organic material using light.

Carbon Dioxide + Water (in the presence of sunlight) produces Glucose + Oxygen.

Carbon dioxide,inorganic form of carbon

Glucose, organic form of

carbon

sunlight

Photosynthesis happens on land…

…and in lakes and oceans

• Consumers — Consume organic matter to provide themselves with energy and organic matter necessary for growth and survival.

– Primary Consumers • Herbivores (eat plants)

– Secondary Consumers • Carnivores (eat other animals)• Omnivores (eat plants and other animals)

Roles of Organisms• Decomposers

– Digest organic molecules from dead organisms into simpler organic compounds, and absorb the nutrients. (Bacteria and fungi)

• Use non-living organic matter as source of energy.

*without decomposers, dead things would pile up

Energy Flow

Each step in the flow of energy through the food chain known as a trophic level.

Energy Flow

As energy moves from one trophic level to the next, most of the useful energy (90%) is lost as heat.

2nd Law of Thermodynamics (remember what a law is?)

When matter is converted from one form to another, energy is lost

• Food Chain — Passage of energy from one trophic level to the next due to one organism consuming another.

Not very realistic…what about all those other interactions we talked about?

Food Chains and Food Webs

Food Web — Series of multiple food chains.

Bioaccumulation - an accumulation of a contaminant in an organism at a higher trophic level

PCBs – Polychlorinated biphenyls

Chlorodanes

methyl - mercury

Energy is not the only thing moving up the food chain

PCBsA group of more than 200 man-made chemicals that were used as insulating fluid for electrical equipment like capacitors and transformers.

PCBs accumulate in the fat of people and animals.

In 1979, the U.S. Environmental Protection Agency (USEPA) banned all use of PCBs; however, PCB removal or replacement is not required for equipment that already contained these chemicals.

Because of the health effects associated with exposure, commercial production of PCBs ended in 1977.

More than 1 billion pounds of PCBs were manufactured in the United States.

below 0.05 unrestricted0.05 - 0.2 1 meal per week0.2 - 1.0 1 meal per month1.0 - 2.0 6 meals per yearabove 2.0 no consumption

PCB Concentration (parts per million) Advisory Category

Fish Consumption advisories

www.idph.state.il.us/envhealth/fishadv/fishadvisory03.htm

All Sizes 1 meal/week

Chinook Salmon Coho Salmon Rainbow Trout Brown Trout

Less than 30" 1 meal/month

Larger than 30”6 meals/year

All Sizes1 meal/month

Less than 17" 1 meal/week

Larger than 17" 1 meal/month

Less than 22" 1 meal/month

Larger than 22”6 meals/year

Channel Catfish Lake Trout Yellow Perch Carp

All SizesDo Not Eat

Less than 23" 1 meal/month

23" to 27”6 meals/year

Larger than 27”Do Not Eat

All SizesDo Not Eat

Nutrient Cycles in Ecosystems

• Organisms are composed of molecules and atoms that are cycled between living and non-living portions of an ecosystem.

• Biogeochemical Cycles– Carbon

– Nitrogen

– Phosphorus

Nutrient Cycles

• Consuming prey, excretion, and decomposition all contribute to cycling of major nutrients

• Three of the most important elements:– Carbon, Nitrogen, Phosphorous

• Cycles describe how inorganic forms are converted to organic forms, used by organisms, and released as inorganic forms

Why care about Carbon?

Life as we know it is Carbon based

Most of our energy comes from carbon-based compounds

CO2 is a greenhouse gas

CO2 is a greenhouse gas one that absorbs infrared radiation and warms surface air

Carbon Cycle• Carbon and Oxygen combine to form

Carbon Dioxide (CO2).

• Plants use Carbon Dioxide during photosynthesis to produce sugars.

• Plants use sugars for plant growth.

Carbon Cycle

• Herbivores eat plants, and incorporate molecules into their structure.

• Respiration breaks down sugars releasing CO2 and water back into the atmosphere.

Why care about Nitrogen?

Nitrogen is also important in biomolecules

Amino acid

Nitrogen is often limiting for plants, esp. crops

Nitric Acid (HNO3) is a component of acid rain

Nitrogen cycle

• Nitrogen often a limiting resource for plants– Farmers try to increase nitrogen

availability

– Can use fertilizer• Runoff then can pollute aquatic systems

– Or rotate crops• Soy has symbiotic nitrogen-fixing bacteria

Why care about P

Phosphorus is vital to life (ATP, phospholipid membranes, etc.)

Phosphorus is often a limiting nutrient for algae

Phosphorus pollution has been responsible for algal blooms in many lakes

Phosphorous cycle

• Main source is weathering of rocks

• Dissolved in water

• Plant uptake, animals consume plants

• Decomposers use dead organic matter, waste products

• Some waste products become dissolved in water and lost as deposits

Human Impact on Nutrient Cycles

• Human activities have caused significant changes in biogeochemical cycles:

– Burning Fossil Fuels.

– Converting forests to agricultural land.

• Fertilizer carried into aquatic ecosystems.

• Increase aquatic plant growth rate.

–Lowered oxygen concentrations.

Points to Know1. The difference between populations, communities, and

ecosystems

2. Characteristics of each trophic level – how does it get its energy/nutrients? What moves behind different levels?

3. What is photosynthesis and why does it matter for organisms besides plants?

4. How does biomass change as one moves up or down the food chain? Why?

5. Major features of the carbon, nitrogen, and phosphorus cycles

6. How can humans change nutrient cycles?