Ch 54 - Ecosystems

What is an ecosystem?

• All organisms in a community and the abiotic factors they interact with

Physical Laws & Energy

• Law of conservation of energy – energy cannot be created or destroyed, only transferred or transformed

• 2nd law of thermodynamics – every exchange of energy increases the entropy of the universe

• Thus ecosystems need a constant supply of energy

Energy flow in ecosystems

• Energy flows through the ecosystem –one way

• Sun is primary source of energy

Trophic levels

• Autotrophs – primary producers – plants, phytoplankton

• Heterotrophs – consumers– Primary consumers – herbivores– Secondary consumers – carnivores that eat

herbivores– Tertiary consumers – carnivores that eat other

carnivores

• Decomposers/Detritivores- get energy from detritus– prokaryotes & fungi are main decomposers– Decomposition connects all trophic levels

– http://www.countrysideinfo.co.uk/rabbita.htm– http://vimeo.com/21216124

KeyChemical cyclingEnergy flow

Sun

Heat

Primary producers

Primaryconsumers

Secondary andtertiary consumers

Detritus

Microorganismsand other

detritivores

Primary production

• Most ecosystems - primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period

• In a few ecosystems, chemoautotrophs are the primary producers

GPP vs. NPP

• Gross primary production – total primary production

• Net primary production:• = GPP minus energy used by primary

producers for respiration• On average NPP is ½ of GPP• This is the amount of energy available to consumers

Net primary production(kg carbon/m2yr)

3

2

0

1

Global net primary production

Primary production in Aquatic systems• Factors:

– Light limitation– Nutrient limitation

Commonly nitrogen & phosphorous

• Eutrophication– Process where bodies of water receive too many

nutrients, which results in excessive plant growth, reducing oxygen concentration & water clarity

Primary production in Terrestrial ecosystems

• Factors– Temperature– Moisture– Nutrients

Plant adaptations for nutrients

• Symbiotic relationships:• Nitrogen fixing bacteria –

– Convert N2 to NH3 – Rhizobium forms nodules on roots of

legumes

• Mycorrhizae -– Host plant provides fungus with sugar– Fungus increases surface area for water

uptake, and supplies plant with minerals absorbed from soil

Secondary production

The amount of chemical energy from food that is converted to a consumer’s biomass

Trophic efficiency

• 10% rule• Only 10% of energy available at one trophic

level is transferred to the next trophic level

• 90% of energy is not transferred:– Not eaten, lost through respiration, contained in

feces– http://science.howstuffworks.com/life/27995-assi

gnment-discovery-energy-flow-video.htm

Pyramid of energy

Biogeochemical Cycles

Matter gets recycled

Phosphorus Cycle

Carbon Cycle