Human Domination of Ecosystems NSES 2'6 Vitousek et al'

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Human Domination of Ecosystems(NSES 2.6 Vitousek
et al.)

• What do humans do to ecosystems?
• Impact can be direct and intentional (e.g.
  hunting, fishing, habitat destruction) or
  indirect and unintentional (e.g. CO2 production,
  ozone loss, habitat fragmentation, pollution)

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Human Domination of Ecosystems

• Land transformation
• 10-15 of Earth surface is used for row-crops
  agriculture or urban areas
• 6-8 has been converted to pastureland
• Some modification is less intense or permanent
  (e.g. use of existing grassland for grazing,
  harvesting wood from forests)
• Fraction of land transformed or degraded by
  humans is estimated at 39-50

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Human Domination of Ecosystems

• Land transformation
• Primary driving force behind loss of biodiversity
• Major component (20) of human-generated CO2
  emissions through burning also important in
  methane and NO2 emissions
• Changes weathering and runoff patterns, air
  circulation, weather patterns (temperature,
  rainfall)

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Human Domination of Ecosystems

• Oceans and marine ecosystems
• About 60 of humans are within 100 km of a coast
• Humans use about 8 of total ocean productivity,
  but that is concentrated in coastal upwelling
  zones and on temperate continental shelf
• 44 of fisheries are at or above the limits of
  exploitation 22 of fisheries are overexploited

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Human Domination of Ecosystems

• Oceans and marine ecosystems
• Almost 1/4 of global catch is non-target
  organisms and is discarded
• Fishing focuses at upper trophic levels,
  sometimes causing harmful disruptions of food
  chains (e.g. algal blooms)

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Human Domination of Ecosystems

• Biogeochemical cycles
• Carbon - Most profound of all chemical cycles is
  human-induced increase in CO2
• Increase is about 15 in the past 50 years
  probably about 30-40 over pre-industrial levels,
  and still increasing.
• Affects plant growth and also global temperatures
  and thus climate and weather.

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Global Warming and CO2
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Human Domination of Ecosystems

• Biogeochemical cycles
• Water - most is saline or frozen, but humans use
  more than half of freshwater runoff (rivers,
  lakes, dams).
• About 70 of this goes toward agriculture. Only
  2 of U.S. rivers are undammed (33 globally).
• 6 of global river water is evaporated due to
  human manipulation some rivers no longer reallly
  reach the ocean

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Human Domination of Ecosystems

• Biogeochemical cycles
• Nitrogen - Most nitrogen is unusable by organisms
  (atmospheric N2), but nitrogen is a required
  nutrient. It is only useful to organisms when
  chemically fixed (combined with H, O, or C).
• Natural nitrogen fixing is about 90-130
  teragrams (Tg) on land and about that much in the
  ocean.

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Human Domination of Ecosystems

• Biogeochemical cycles
• Humans fix nitrogen for fertilizer, adding
  between 10 Tg (1950) to 80 Tg (1990) and up to
  135 T by 2030.
• Human crops add another 40 Tg annually
• Burning fossil fuels adds another 20 Tg (by
  releasing fossil N and by fixing new N during
  burning)
• Fixed N can contribute to smog and acid rain it
  is also a limiting nutrient in many ecosystems,
  so it can increase productivity (but usually at
  the expense of diversity)

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Human Domination of Ecosystems

• Biogeochemical cycles
• Organic compounds - e.g. DDT, PCB, CFC
• Most that have caused damage have been released
  with little testing -- the damage was noted over
  the course of years or decades the compound was
  phased out, but then may persist for many years
  after use ceases.
• This is still the model today - 1,000 new organic
  chemicals are developed and manufactured annually
  for various purposes

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Human Domination of Ecosystems

• Biotic changes
• Extinctions - extinctions are natural (well over
  99.999 of all species are now extinct)
• Huge extinctions are natural but rare
• Permo-Triassic boundary defined by 95 of all
  marine species, 57 of families going extinct
  over a geologically short period (lt 1 million
  years)
• K-T boundary showed 85 of species, 20 of
  families, including almost all large animals

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Human Domination of Ecosystems

• Biotic changes
• Extinctions - rates now appear to be about
  100-1000 times higher than pre-human times, but
  that is very hard to calculate
• About 25 of bird species have been lost over the
  past 2000 years

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Human Domination of Ecosystems

• Biotic changes
• 11 of birds, 18 of mammals, 5 of fish, and 8
  of plants are currently endangered
• There is significant damage/change to ecosystems
  even without global extinction
• Invasions also important - up to 20 non-native
  on continents, 50 on some islands

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Human Population and Limits(Cohen, NSES 11.3)

• Biological population modeling has been applied
  to human populations
• Normally, this includes a standard reproductive
  rate applied to existing population in a series
  of time steps
• It normally also includes a death rate this may
  be proportional to population overcrowding or
  competition for resources

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Rates of Change

• If birth rate is proportional to population, then
  exponential growth may occur
• If there is a death rate that is proportional to
  population size, then there is the concept of a
  carrying capacity in a given environment - the
  total number of organisms that the environment
  can support. This is logistic growth.

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Exponential Growth

• Growth is when population is increasing
• Exponential growth is when the rate at which
  population increases is accelerating
• Usually means that the rate of growth is
  proportional to the current size of the
  population
• Usually also means there are no ultimate
  restrictions on growth (growth is unbounded)

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Exponential Growth
Data from J. Covacevich and M. Archer, referenced
at University of Minnesota Calculus Initiative,
http//www.geom.umn.edu/education/calc-init/popula
tion
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Exponential Growth Modeling

• Mathematically
• Pt P0 ekt
• P population, k constant, t time, e2.71828
• Whats this mean?
• The population at any later time (Pt) is equal to
  the population now (P0) times an exponential
  function. If k is positive, the population will
  increase very rapidly

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Exponential Growth Model
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Logistic Growth

• Logistic growth adds the concept of carrying
  capacity.
• Mathematically
• Change in P Pk(1-P/CC)
• P population kgrowth rate per time unit CC
  carrying capacity
• Whats this mean?
• The population size grows each year by some rate
  (k), but that rate decreases to zero as the
  population approaches the carrying capacity.

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Logistic Growth
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Human Population

• The carrying capacity of a certain environment
  for a certain organism can change, particularly
  when the organism in question is humans
• Development of agricultural technology has
  increased the carrying capacity of almost all
  parts of the Earth by increasing food production
• This technology and production may not be
  sustainable, however - it depends on fertilizers,
  herbicides, irrigation, and fossil fuels

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Population Growth
Source PBS, Paul Ehrlich and the Population Bomb
teacher resources http//www.pbs.org/kqed/populati
on_bomb/hope/teacher.html
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Human Population Growth
Time unit Births Deaths Natural
Increase Year 131,468,233 54,147,021 77,321,212
Month 10,955,686  4,512,252  6,443,434  Day 360,1
87 148,348 211,839 Hour 15,008  6,181 8,827 Minu
te 250 103 147 Seconds 4.2 1.7 2.5
Data source, this and subsequent slides U.S.
Census Data, cited at Negative Population Growth
(www.npg.org)
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Global Population
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Global Population Growth
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Global Population Growth
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U.S. Population Change
One birth every 8 seconds One death every 13
seconds  One international migrant (net)
every 30 seconds  One Federal U.S. citizen (net)
returning every 4724 seconds Net gain of one
person every 12 seconds
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U.S. Population Change
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U.S. Population Change
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U.S. Population Change
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Predicted U.S. Population
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Human Carrying Capacity

• So, is there a real carrying capacity for humans
  on Earth?
• It is rapidly changing -
• Increases due to technology, medicine,
  agriculture, etc.
• Decreases due to consumption of non-renewable
  resources, environmental degradation
• Life at the carrying capacity would likely be
  psychologically intolerable and avoided