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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

Chapter 54
  • Ecosystems

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

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
  • Play a central role in material cycling

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

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

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

Global Energy Budget
  • Each day Earth receives 1022joules of solar
  • 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
  • But producers generate 170 billion tons of
    organic matter a year

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)

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)

Earths Ecosystems and Biomass
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

Production in Marine Ecosystems
  • Limiting nutrient
  • Nutrients that must be added for production to
  • In marine ecosystems nitrogen and phosphorus are
  • 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

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

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

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

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
  • 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
  • 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

Efficiency of Energy Transfer
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

Energy efficiency of trophic levels
Pyramids of numbers
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
  • Total of 830,000,000,000 metric tons of carbon in
  • 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

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.

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
  • Soil is the main reservoir

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

Water Cycle
Nitrogen Cycle
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

Carbon Cycle
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

Phosphorus Cycle
Decomposition and Nutrient Cycling
  • Different ecosystems cycle nutrients at different
  • 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
  • why?
  • Nutrients are taken up as soon as they are
  • Rain forest soil is very poor

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

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

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

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
  • pH less than 5.6
  • Some parts of Europe receive rain with a pH of
  • 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

Acid Precipitation
  • 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

Biological Magnification
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

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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
  • Central US would be much drier

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

Ozone Depletion