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Ecosystems

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Earthworms eat soil and extract nutrients and birds eat worms. Worms cant eat dirt ... Acid rain causes leaching of nitrogen and phosphorus from the soil ... – PowerPoint PPT presentation

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Title: Ecosystems


1
Chapter 54
  • Ecosystems

2
What is an Ecosystem?
  • All organisms living in an area plus the abiotic
    factors
  • Energy machines and matter processors
  • Energy flows through and matter cycles

3
Trophic Relationships
  • Primary producers
  • Ultimately support all trophic levels
  • Autotrophic organisms
  • Organisms above producers
  • Heterotrophic
  • Depend on photosynthetic output of producers
  • Decomposers
  • Get energy from detritus (nonliving organic
    material)
  • Play a central role in material cycling

4
Decompositions Role
  • Decomposers link all trophic levels
  • Re-supply ecosystems with organic material
  • Liberate otherwise unusable material
  • Earthworms eat soil and extract nutrients and
    birds eat worms
  • Worms cant eat dirt

5
Laws of Physics and Chemistry
  • First law of thermodynamics
  • Energy is neither created nor destroyed, only
    transformed
  • Second law of thermodynamics
  • Energy is lost when it changes states
  • Chemistry laws
  • Energy moves through an ecosystem
  • Nutrients cycle through an ecosystem

6
Primary Producers
  • Organisms that convert energy from the sun into
    chemical energy (stored in bonds of sugars)
  • Primary producers provide all the energy for a
    given ecosystem
  • Lots of plants means lots of energy

7
Global Energy Budget
  • Each day Earth receives 1022joules of solar
    radiation
  • Equivalent of 100 million atomic bombs
  • Most of that energy is reflected by the
    atmosphere, or absorbed by water or the ground
  • Plants only use the part of solar radiation we
    call visible light
  • Of visible light only 1 is converted to organic
    matter
  • But producers generate 170 billion tons of
    organic matter a year

8
Gross and Net Primary Production
  • Gross Primary Production
  • Amount of light energy converted to chemical
    energy by photosynthesis per unit of time
  • Not all of this production is stored as organic
    material because the plants use some molecules as
    fuel for respiration
  • Net Primary Production
  • Amount of chemical energy available to the next
    trophic level
  • NPP GPP R (respiration)

9
Net Primary Production
  • Measurement of most interest to ecologists
  • Primary production can be expressed as biomass
    (weight of vegetation added to ecosystem per area
    per time or g/m2/yr) or energy per area per unit
    time or (J/m2/yr)

10
Earths Ecosystems and Biomass
11
Production in Marine Ecosystems
  • Limiting factors in Marine Ecosystems
  • Light more than half the light is absorbed in
    the first meter of water
  • Even clear water at 20 m only 5-10 of the light
    is available
  • We should then see an increase in production from
    poles toward the equator but we dont
  • Its actually nutrients that are more limiting in
    marine ecosystems than light

12
Production in Marine Ecosystems
  • Limiting nutrient
  • Nutrients that must be added for production to
    increase
  • In marine ecosystems nitrogen and phosphorus are
    limiting
  • Iron is also limiting in parts of the ocean
  • Iron is supplied by wind blown dust
  • Where iron is abundant so is nitrogen
  • Cyanobacteria need iron to fix atmospheric
    nitrogen into a useable form

13
Production in Freshwater Ecosystems
  • Limiting factors
  • Light
  • Temperature
  • Nutrients unlike marine ecosystems, phosphorus
    is the main limiting factor

14
Terrestrial Ecosystems
  • Main factors are
  • Water
  • Temperature
  • Nutrients

15
Secondary Production in Ecosystems
  • Amount of chemical energy in food converted into
    organic matter
  • Cow eats grass secondary production is the
    amount of grass that is converted into cow
  • The cow does not use the entire grass, some of it
    passes through the digestive system

16
Production Efficiency
  • Example of a caterpillar
  • Eats 200 J of plant material
  • 33 J is used for growth
  • 100 J passes through the caterpillar as feces
  • Not lost energy because decomposers will use this
    energy
  • 67 J is used for cellular respiration
  • This energy is lost as heat
  • Efficiency measure
  • Production efficiency net secondary production
    / assimilation of primary production
  • Fraction of food energy that is not used for
    respiration, or energy that is not lost to the
    environment
  • Our example production efficiency 33 J (growth)
    / 33 67 J (energy used for assimilation, feces
    dont count) 33
  • Birds and mammals average 1-3
  • Fish average 10
  • Insects average 40

17
Efficiency of Energy Transfer
18
Trophic Efficiency and Ecological Pyramids
  • Trophic efficiency percentage of production
    transferred from trophic level to the next
  • Generally only 10 of the total energy at one
    level is available for use at the next level

19
Energy efficiency of trophic levels
20
Pyramids of numbers
21
Green World Hypothesis
  • With so many primary consumers (herbivores) why
    is everything still so green
  • Herbivores actually consume very little plant
    biomass because they are held in check by several
    factors
  • Total of 830,000,000,000 metric tons of carbon in
    plants
  • 50,000,000,000 tons is added each year
  • Herbivores only consume 17 of this biomass every
    year so they are just really a nuisance to plants
  • Factors that keep herbivores in check
  • Plant defenses
  • Nutrients, not energy supply, limit herbivores
  • Abiotic factors
  • Intraspecific competition
  • Interspecific interactions

22
Cycling of Elements
  • Solar energy is replenished daily
  • Carbon, Nitrogen, Phosphorus, etc. are not
    replenished (at all)
  • Earth relies on the cycling of these nutrients.

23
Biological and Geological Processes That Drive
Nutrient Cycling
  • Biogeochemical cycles nutrient pathways that
    involve both living and nonliving processes
  • Two general paths for chemicals
  • Global gaseous forms of chemicals that can move
    through the atmosphere (N, C, O, S)
  • Atmosphere is the main reservoir
  • Local less mobile in the environment (P, K, and
    Ca)
  • Soil is the main reservoir

24
General Model of Chemical Cycling
  • Shows the main reservoirs and general processes
    that involve moving chemicals from one reservoir
    to the next
  • Most nutrients accumulate in 4 reservoirs defined
    by two characteristics
  • Whether it contains organic or inorganic material
  • Whether it is available for use or not
  • Cycling of water does not fit this model well

25
Water Cycle
26
Nitrogen Cycle
27
Nitrogen Cycle
  • Earths atmosphere is about 80 nitrogen
  • It is in an unusable form (N2)
  • Usable nitrogen (NH4 or NO3enters ecosystems two
    ways (depends on the ecosystem)
  • Atmospheric deposition (5-10)
  • Added by being dissolved in rain or settling as
    fine dust
  • Nitrogen fixation
  • Only certain bacteria can fix atmospheric
    nitrogen into usable form
  • Bacteria are either free living or part of
    symbiotic relationship (Rhizobium)
  • One unnatural way is through the use of
    fertilizers by humans
  • Runoff from fields

28
Carbon Cycle
29
Phosphorus Cycle
  • Organisms require phosphorus for DNA, ATP, and
    phospholipids (cell membranes)
  • Does not include the atmosphere
  • No significant phosphorus containing gases
  • Usable form is PO43- which plants can absorb
  • Main reservoir is rock

30
Phosphorus Cycle
31
Decomposition and Nutrient Cycling
  • Different ecosystems cycle nutrients at different
    rates
  • Depends on rate of decomposition
  • Tropical rain forest few months to few years
  • Temperate forests 4 to 6 years
  • Tundra 50 years
  • Temperature and oxygen play vital roles
  • Tropical rain forests phosphorus occurs in the
    soil at levels far below that of a temperate
    forest
  • why?
  • Nutrients are taken up as soon as they are
    available
  • Rain forest soil is very poor

32
Human Impact on Ecosystems and Biosphere
  • Disruption of chemical cycles
  • Depletion of soil nutrients in one area, and
    excess in another
  • Food crops
  • Addition of new toxins to an area
  • Agricultural effects on nutrient cycling
  • An area is cleared for farming, and nutrients
    exist in the soil
  • The crop is grown, but the nutrients the crop
    took from the soil is transported elsewhere
  • Nutrients must be added back to the soil
  • Nitrogen is a big limiting factor

33
Critical Load and Nutrient Cycles
  • Excess nitrogen minerals in the soil are leaking
    into rivers, and eventually the ocean
  • This does have positive effects for some forests
  • Nitrogen runoff fertilizes forests
  • Critical Load amount of nutrients that begins
    to have negative affects

34
Accelerated Eutrophication of Lakes
  • Eutrophic lake high in nutrients
  • Oligotrophic low in nutrients
  • Sewage and factory runoff adds nutrients to lakes
  • Results in explosive increase of phytoplankton
  • Banks become choked with weeds
  • Algae blooms deplete oxygen content
  • Results in fish death

35
Combustion of Fossil Fuels and Acid Rain
  • Burning wood, coal, and oil results in release of
    oxides of sulfur and nitrogen that react with
    water to form sulfuric and nitric acid
  • These fall back to the earth as acid
    precipitation
  • pH less than 5.6
  • Some parts of Europe receive rain with a pH of
    3.0
  • Acid rain causes leaching of nitrogen and
    phosphorus from the soil
  • Lakes and streams are heavily damaged due to slow
    buffering capacity
  • Results in predator death and replacement with
    acid tolerant species which affects the food web

36
Acid Precipitation
37
Toxins
  • Synthetic materials that become concentrated in
    ecosystems due to the inability of organisms to
    break it down
  • Mercury in waters
  • Becomes part of fish tissue and humans can die
    from eating these fish
  • DDT and biological magnification
  • Top level carnivores are the most severely
    affected by these toxins

38
Biological Magnification
39
Climate Change
  • Rising CO2 levels in the atmosphere
  • Caused by combustion of fossil fuels and wood
    from deforestation
  • CO2 concentration before 1850 274 ppm
  • 1958 316 ppm
  • Today 370 ppm
  • Greenhouse effect
  • CO2 and water vapor absorb and reflect much of
    the solar radiation that reaches Earth
  • Increase CO2 means more absorption
  • Its like thickening the glass of a greenhouse, it
    will raise the temperature

40
(No Transcript)
41
Global Warming
  • Hard to understand due to all the abiotic and
    biotic factors
  • Predictions and estimations
  • End of 21st century CO2 concentrations double and
    average global increase of 2 C
  • Increase of 1.3 C would make the world warmer
    than any time in the past 100,000 years
  • Polar ice would melt and raise the sea level by
    100 m (New York, Miami, and LA would be under
    water)
  • Central US would be much drier

42
Ozone Depletion
  • Ozone protects us from harmful UV radiation
  • Ozone is O3 it absorbs UV rays
  • been gradually thinning since 1975
  • Due to increase of CFCs (use in refrigeration)
  • May cause increase of skin cancer and cataracts

43
Ozone Depletion
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