1. Ecosystems

2. Studying organisms in their environment
biosphere
ecosystem
community
population
organism
An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact
Ecosystems range from a microcosm, such as an aquarium, to a large area such as a lake or forest

3. Essential questions What limits the production in ecosystems?
How do nutrients move in the ecosystem?
How does energy move through the ecosystem?
Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling
Energy flows through ecosystems while matter cycles within them

4. Ecosystem All the organisms in a community plus abiotic factors
ecosystems are transformers of energy & processors of matter
Ecosystems are self-sustaining
what is needed?
Ecologists study the transformations of energy and matter within their system
capture energy
transfer energy
cycle nutrients

5. Ecosystem inputs nutrients cycle inputs energy nutrients
biosphere
energy flows through
constant input of energy
nutrients cycle
Matter cannot
be created or destroyed
Don’t forget the laws of Physics!
Laws of physics and chemistry apply to ecosystems, particularly energy flow
The first law of thermodynamics states that energy cannot be created or destroyed, only transformed
Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat
The second law of thermodynamics states that every exchange of energy increases the entropy of the universe
In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heat
The law of conservation of mass states that matter cannot be created or destroyed
Chemical elements are continually recycled within ecosystems
In a forest ecosystem, most nutrients enter as dust or solutes in rain and are carried away in water
Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products
In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on four factors:
Each chemical’s biological importance
Forms in which each chemical is available or used by organisms
Major reservoirs for each chemical
Key processes driving movement of each chemical through its cycle
nutrients can only cycle
inputs
energy
nutrients

6. Generalized Nutrient cycling
consumers
consumers
consumers
producers
decomposers
decomposers
nutrients ENTER FOOD CHAIN = made available to producers
nutrients made available to producers
return to abiotic reservoir
Decomposition connects all trophic levels
Life depends on recycling chemical elements
Nutrient circuits in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles
Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally
Less mobile elements such as phosphorus, potassium, and calcium cycle on a more local level
A model of nutrient cycling includes main reservoirs of elements and processes that transfer elements between reservoirs
All elements cycle between organic and inorganic reservoirs
Decomposers (detritivores) play a key role in the general pattern of chemical cycling
Rates at which nutrients cycle in different ecosystems vary greatly, mostly as a result of differing rates of decomposition
The rate of decomposition is controlled by temperature, moisture, and nutrient availability
Rapid decomposition results in relatively low levels of nutrients in the soil
Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source; heterotrophs depend on the biosynthetic output of other organisms
Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores)
Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter
Prokaryotes and fungi are important detritivores
Decomposition connects all trophic levels
abiotic reservoir
abiotic reservoir
geologic processes
geologic processes

7. Carbon cycle abiotic reservoir: CO2 in atmosphere enter food chain:
photosynthesis = carbon fixation in Calvin cycle
recycle:
return to abiotic:
respiration
combustion
Carbon cycle
CO2 in
atmosphere
Diffusion
Respiration
Photosynthesis
Plants and algae
Plants
Animals
Industry and home
Combustion of fuels
Carbonates in sediment
Bicarbonates
Deposition of
dead material
Deposition
of dead
material
Fossil fuels
(oil, gas, coal)
Dissolved CO2
The Carbon Cycle
Carbon-based organic molecules are essential to all organisms
Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, and the atmosphere
CO2 is taken up and released through photosynthesis and respiration; additionally, volcanoes and the burning of fossil fuels contribute CO2 to the atmosphere

8. Nitrogen cycle Atmospheric nitrogen Carnivores Herbivores Birds Plants
abiotic reservoir:
N in atmosphere
enter food chain:
nitrogen fixation by soil & aquatic bacteria
recycle:
decomposing & nitrifying bacteria
return to abiotic:
denitrifying bacteria
Atmospheric
nitrogen
Carnivores
Herbivores
Birds
Plankton with
nitrogen-fixing
bacteria
Plants
Death, excretion, feces
The Terrestrial Nitrogen Cycle
Nitrogen is a component of amino acids, proteins, and nucleic acids
The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be converted to NH4+ or NO3– for uptake by plants, via nitrogen fixation by bacteria
Organic nitrogen is decomposed to NH4+ by ammonification, and NH4+ is decomposed to NO3– by nitrification
Denitrification converts NO3– back to N2
The quality of soil varies with the amount of organic material it contains
Agriculture removes from ecosystems nutrients that would ordinarily be cycled back into the soil
Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly affects the nitrogen cycle
Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful
Critical load for a nutrient is the amount that plants can absorb without damaging the ecosystem
When excess nutrients are added to an ecosystem, the critical load is exceeded
Remaining nutrients can contaminate groundwater as well as freshwater and marine ecosystems
Sewage runoff causes cultural eutrophication, excessive algal growth that can greatly harm freshwater ecosystems
Fish
Nitrogen-fixing
bacteria
(plant roots)
Decomposing bacteria
amino acids
excretion
Ammonifying bacteria
Nitrogen-fixing
bacteria
(soil)
loss to deep sediments
Nitrifying bacteria
Denitrifying
bacteria
soil nitrates

9. Phosphorus cycle abiotic reservoir: rocks, minerals, soil
enter food chain:
erosion releases soluble phosphate
uptake by plants
recycle:
decomposing bacteria & fungi
return to abiotic:
loss to ocean sediment
Phosphorus cycle
Land
animals
Plants
Animal tissue
and feces
Urine
Soluble soil
phosphate
Decomposers
(bacteria and
fungi)
Loss in
drainage
Rocks and
minerals
Phosphates
in solution
Decomposers
(bacteria & fungi)
The Phosphorus Cycle
Phosphorus is a major constituent of nucleic acids, phospholipids, and ATP
Phosphate (PO43–) is the most important inorganic form of phosphorus
The largest reservoirs are sedimentary rocks of marine origin, the oceans, and organisms
Phosphate binds with soil particles, and movement is often localized
Animal tissue
and feces
Aquatic
animals
Plants and
algae
Precipitates
Loss to deep sediment

10. Water cycle Solar energy Transpiration Evaporation Precipitation
abiotic reservoir:
surface & atmospheric water
enter food chain:
precipitation & plant uptake
recycle:
transpiration
return to abiotic:
evaporation & runoff
Water cycle
Solar energy
Transpiration
Water vapor
Evaporation
Precipitation
Oceans
The Water Cycle
Water is essential to all organisms
97% of the biosphere’s water is contained in the oceans, 2% is in glaciers and polar ice caps, and 1% is in lakes, rivers, and groundwater
Water moves by the processes of evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater
Runoff
Lakes
Percolation in soil
Aquifer
Groundwater

11. Transpiration
In terrestrial ecosystems, temperature and moisture affect primary production on a large scale
Actual evapotranspiration can represent the contrast between wet and dry climates
Actual evapotranspiration is the water annually transpired by plants and evaporated from a landscape
It is related to net primary production

12. Breaking the water cycle
Deforestation breaks the water cycle
groundwater is not transpired to the atmosphere, so precipitation is not created
forest  desert
desertification

13. Repairing the damage The Greenbelt Movement planting trees in Kenya
restoring a sustainable ecosystem
establishing democracy
empowering women
Wangari Maathai
Nobel Peace prize 2004

14. Effects of deforestation
40% increase in runoff
loss of water
60x loss in nitrogen
10x loss in calcium
loss into surface water 80
nitrate levels in runoff 40
loss out of ecosystem!
of nitrate (mg/l )
Concentration 4
Deforestation 2
Why is nitrogen so important?
1965
1966
1967
1968
Year

15. Ecosystem inputs nutrients cycle inputs energy nutrients
biosphere
energy flows through
nutrients cycle
inputs
energy
nutrients

16. Energy flows through ecosystems
sun
secondary consumers
(carnivores)
loss of energy
loss of energy
primary consumers
(herbivores)
Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores)
Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter
Prokaryotes and fungi are important detritivores
Decomposition connects all trophic levels
Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period
The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget
Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time
producers (plants)

17. Gross and Net Primary Production
Total primary production is known as the ecosystem’s gross primary production (GPP)
Net primary production (NPP) is GPP minus energy used by primary producers for respiration
Only NPP is available to consumers
Ecosystems vary greatly in NPP and contribution to the total NPP on Earth
Standing crop is the total biomass of photosynthetic autotrophs at a given time
More than light, nutrients limit primary production in geographic regions of the ocean and in lakes
A limiting nutrient is the element that must be added for production to increase in an area
Nitrogen and phosphorous are typically the nutrients that most often limit marine production
Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth off the shore of Long Island, New York
The addition of large amounts of nutrients to lakes has a wide range of ecological impacts
In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of most fish species

18. Food chains Trophic levels sun feeding relationships
Tertiary consumer
Trophic levels
feeding relationships
start with energy from the sun
captured by plants
1st level of all food chains
food chains usually go up only 4 or 5 levels
inefficiency of energy transfer
all levels connect to decomposers
top carnivore
Level 3
Secondary consumer
carnivore
Level 2
Primary consumer
heterotrophs
herbivore
Level 1
Producer
autotrophs
Fungi
Decomposers
Bacteria

19. Inefficiency of energy transfer
sun
Inefficiency of energy transfer
Loss of energy between levels of food chain
To where is the energy lost? The cost of living!
17%
growth
When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production
An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration
energy lost to daily living
only this energy moves on to the next level in the food chain
33%
cellular
respiration
50%
waste (feces)

20. Ecological pyramid sun Loss of energy between levels of food chain
can feed fewer animals in each level 1
100
Trophic efficiency is the percentage of production transferred from one trophic level to the next
It usually ranges from 5% to 20%
Trophic efficiency is multiplied over the length of a food chain
Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer
A pyramid of net production represents the loss of energy with each transfer in a food chain
In a biomass pyramid, each tier represents the dry weight of all organisms in one trophic level
Most biomass pyramids show a sharp decrease at successively higher trophic levels
100,000
1,000,000,000

21. What is your ecological footprint?!
Humans in food chains
Dynamics of energy through ecosystems have important implications for human populations
how much energy does it take to feed a human?
if we are meat eaters?
if we are vegetarian?
What is your ecological footprint?!
Dynamics of energy flow in ecosystems have important implications for the human population
Eating meat is a relatively inefficient way of tapping photosynthetic production
Worldwide agriculture could feed many more people if humans ate only plant material

22. Food webs Food chains are linked together into food webs
Who eats whom?
a species may weave into web at more than one level
bears
humans
eating meat?
eating plants?