Introduction to Ecology

1
Introduction to Ecology

• Chapters 52

2
Figure 50.3 Rachel Carson
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Ecology

• Ecology the study of interactions between
  organisms and the environment
• Biotic living components of an ecosystem (ex.
  animals and plants)
• Abiotic - nonliving components of an ecosystem
  (ex. soil, air, and water)

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Species distribution

• Interactions between organisms and the
  environment limit the distribution of species.
• What affects the distribution of species?
• Dispersal limits (range expansions and species
  transplants)
• Behavior and habitat selections
• Biotic factors (other species)
• Abiotic factors (temperature, water, sunlight,
  wind, rocks/soil, and climate)

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Figure 50.7 Spread of the African honeybee in
the Americas since 1956
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Figure 50.11 Solar radiation and latitude
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Figure 50.12 What causes the seasons?
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Figure 50.14 How mountains affect rainfall
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Figure 50.18 Zonation in a lake
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Figure 50.22 Zonation in the marine environment
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Figure 50.24 The distribution of major
terrestrial biomes
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Figure 50.10 A climograph for some major kinds
of ecosystems (biomes) in North America
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POPULATION ECOLOGY

• CHAPTER 53

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POPULATION CHARACTERISTICS

• Population organisms of the same species in the
  same area
• Density number of individuals in a given area
  (example 1200/m2)
• Dispersion pattern of spacing among individuals

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Measuring Size

• Quadrant method used for stationary organisms
• Mark and recapture used for mobile organisms

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Patterns of Dispersion

• Clumped individuals aggregated in patches (most
  common)
• Uniform evenly spaced individuals
• Random unpredictable, patternless

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Patterns of dispersion within a populations
geographic range
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DEMOGRAPHY

• Demography is the study of factors that affect
  populations
• Age structure relative number of individuals of
  each age
• Birthrate or fecundity number of offspring born
  during a certain time period
• Death rate number of individuals who die in a
  certain time period
• Generation time average span between birth of
  individuals and the birth of their offspring
• Sex ratio proportion of individuals of each sex

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• Life tables used to determine how long, on
  average, an individual of a given age could be
  expected to live
• Cohort group of individuals of same age
• Survivorship curve a plot of the numbers in a
  cohort that are alive at each age

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Life Table for Belding Ground Squirrels
(Spermophilus beldini) at Tioga Pass, in the
Sierra Nevada Mountains of California
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Idealized survivorship curves
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LIFE HISTORIES

• Life history traits that affect an organisms
  schedule of reproduction and death
• Life histories vary greatly
• Salmon travel to ocean to mature and then back to
  stream to reproduce
• Some oaks cannot reproduce until they are at
  least 20 years old
• Semelparity or big bang reproduction produce
  numerous offspring and then die
• Iteroparity or repeated reproduction produce
  fewer offspring over many seasons

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An example of big-bang reproduction Agave
(century plant)
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• There is a trade-off between reproduction and
  survival
• Female red deer who are reproductive have a
  greater chance of dying
• Larger brood sizes increase mortality rate

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Cost of reproduction in female red deer on the
Island of Rhum, in Scotland
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Probability of survival over the following year
for European kestrels after raising a modified
brood
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POPULATION GROWTH

• ?N Change in population size
• B births during time interval (birth rate)
• D deaths during time interval (death rate)
• ?t time interval
• ?N/?t B D
• Per capita birthrate (b) offspring produced
  per time by an average member of population
• Ex. 46 births/year in pop of 1000 so b 46/1000
  0.046
• Birth rate Expected births/year for pop (B)
• BbN
• Ex. B 0.046 x 500 23 births/year (where N
  500)

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• Per capita death rate (m) deaths per time by
  an average member of population
• Ex. 22 deaths/year in pop of 1000 so m 22/1000
  0.022
• Death rate Expected deaths/year for pop (D)
• DmN
• Ex. D 0.022 x 500 11 deaths/year (where N
  500)
• Maximum per capita growth rate (rmax)
• ?N/?t bN mN (birthrate death rate)
• r b m
• ?N/?t rmaxN (exponential growth rate)
• dN/dt rmaxN (calculus version)

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• If a population is growing, r is positive.
• If a population is declining, r is negative.
• Zero population growth occurs when r 0
• Exponential growth maximum population growth
  rate
• Intrinsic rate of increase is the maximum
  population growth rate, rmax
• Exponential growth is
• dN/dt rmax N

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Population growth predicted by the exponential
model
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Example of exponential population growth in
nature
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• Carrying capacity (K) maximum population size
  that a particular environment can support with no
  net increase or decrease
• Logistic Growth incorporates the effect of
  population density on rmax, allowing it to vary
  from rmax under ideal conditions to zero as
  carrying capacity is reached.

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• When N is small compared to K, the per capita
  rate of increase is high. (N pop size)
• When N is large and resources are limiting, the
  per capita rate of increase is small.
• When N K, pop stops growing.
• For logistic growth
• ?N/?t rmaxN (K-N/K)

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Population growth predicted by the logistic model
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How does the logistic curve fit real populations?

• Some populations closely follow the S-shaped
  curve.
• Other populations do not.
• Low numbers may hurt a population (rhinos)
• Populations may overshoot the carrying capacity
  and then drop below K.

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How well do these populations fit the logistic
population growth model?
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Strategies

• K-selected populations (density dependent)
• organisms that are likely to be living at density
  near the limit imposed by the environment (K)
• r-selected populations (density indepedent)
• organisms that are likely to be living in
  variable environments in which populations
  fluctuate or in open habitats where individuals
  are likely to face little competition

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Characteristics r-selected K-selected
Maturation time Short Long
Lifespan Short Long
Death rate Often high Usually low
offspring/episode Many Few
reproductions/ lifetime Usually one Often several
Timing 1st reproduction Early in life Late in life
Size of offspring/eggs Small Large
Parental care none Often extensive
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POPULATION LIMITING FACTORS

• Limiting factors factors that limit population
  growth
• Density dependent factors death rate rises or
  birth rate falls with increasing pop density
• Disease
• Predation
• Competition
• Lack of food
• Lack of space
• Density independent birth rate or death rate
  that does not change with pop density
• Climate

40
Decreased survivorship at high population
densities
41
Long-term study of the moose (Alces alces)
population of Isle Royale, Michigan
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Extreme population fluctuations
43
Population cycles in the snowshoe hare and lynx
44
Human population growth
45
Demographic transition in Sweden and Mexico,
1750-1997
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Age-structure pyramids for the human population
of Kenya (growing at 2.1 per year), the United
States (growing at 0.6 per year), and Italy
(zero growth) for 1995
47
Annual percent increase in global human pop (data
from 2005). Sharp dip in 1960 due mainly to
famine in China that killed 60 million people.
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Infant mortality and life expectancy (from 2005)
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COMMUNITY ECOLOGY

• CHAPTER 54

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COMMUNITIES

• Communities different populations living within
  the same area
• What factors are most significant in structuring
  a community?

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INTERACTIONS

• Interspecific interactions occur between
  different populations within a community
• Coevolution a change in one species acts as a
  selective force on another species, and
  counter-adaptation by the second species, which
  may cause a selective force on the 1st species.

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• Predation (/-)
• Lion hunting, killing, and eating a zebra
• Parasitism (/-)
• Ticks sucking blood of human
• Competition (-/-)
• Fighting over resources
• Commensalism (/0)
• Birds feeding on insects which bison flush out of
  grass
• Mutualism (/)
• Legumes with nitrogen fixing bacteria
• Herbivory (/-)
• Insects eating plants
• Disease (pathogens) (/-)
• Bacteria, viruses, protists, fungi, and prions

53
Figure 53.x2 Parasitic behavior A female
Nasonia vitripennis laying a clutch of eggs into
the pupa of a blowfly (Phormia regina)
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Figure 53.9 Mutualism between acacia trees and
ants. The ants live in the hollow thorns and
sting other pests.
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Predation

• Cryptic coloration camouflage
• Aposematic coloration when animals with
  effective chemical defenses are brightly colored
  as a warning

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Figure 53.5 Camouflage Poor-will (left), lizard
(right)
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Figure 53.6 Aposematic (warning) coloration in a
poisonous blue frog
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Figure 53.x1 Deceptive coloration moth with
"eyeballs"
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• Mimicry an organisms mimic another
• Batesian mimicry a harmless species mimics a
  harmful or unpalatable species
• Mullerian mimicry two or more aposematically
  species resemble each other

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Figure 53.7 Batesian mimicry the hawkmoth larva
resembles a snake
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Figure 53.8 Müllerian mimicry Cuckoo bee
(left), yellow jacket (right)
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Competition

• Competitive exclusion principle two species
  with similar needs for the same limiting
  resources cannot coexist in the same place.
• Could lead to extinction of one species
• Ecological niche ecological role the sum total
  of the organisms use of biotic and abiotic
  resources

63

• Resource partitioning sympatric (geographically
  overlapping) species consume slightly different
  foods or use resources in slightly different
  ways.
• Character displacement characteristics are more
  divergent in sympatric populations compared to
  geographically isolated (allopatric) populations

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Figure 53.3a Resource partitioning in a group of
lizards
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Figure 53.2 Testing a competitive exclusion
hypothesis in the field
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Figure 53.3bc Anolis distichus (left) perches on
sunny areas and Anolis insolitus (right)perches
on shady branches.
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What controls community structure?

• Species diversity
• Food webs
• Dominant species
• Keystone species
• Foundation species

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Figure 53.21 Which forest is more diverse?
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Species Diversity

• Species diversity considers the following
• Species richness number of different species
• Species relative abundance proportion each
  species represents of the total individuals in
  community

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• Dominant species most abundant or highest
  biomass
• Ex. American Chestnut was dominant before 1910,
  but chestnut blight killed all in N. America
• Invasive species can become dominant
• Keystone species a predator that makes an
  unusually strong impact on community structure
• Keystone predators maintain higher species
  diversity by reducing the densities of strong
  competitors, such that the competitive exclusion
  of other species does not occur
• Ex. Removing Piaster decreased species diversity.
  Without piaster, mussels overpopulated and
  excluded other species,

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Figure 53.14b Testing a keystone predator
hypothesis
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Figure 53.14a Testing a keystone predator
hypothesis
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Figure 53.15 Sea otters as keystone predators in
the North Pacific
Without sea otters, sea urchins do well and eat
kelp. Kelp forests are being destroyed. Otters
are being eaten by killer whales.
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• Foundation species - cause physical changes to
  environment
• Ex. beaver dam, black rush (grass) helps prevent
  salt build up in soil of marshes

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Bottom-up or Top-down Controls

• Bottom-up influence from lower to higher
  trophic levels
• Mineral nutrients control the plants, which
  control the herbivores, which then controls the
  predators
• Top-down influence from higher to lower trophic
  levels
• Predators limit herbivores, which in turn limits
  plants, which affects soil nutrients

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DISTURBANCES

• Disturbances are events such as fire, storms,
  drought, or human activities that damage
  communities.
• Can create opportunities for other species
• Human disturbance is not always negative
• Yellowstone fire in 1988 killed old forest, but
  new plants quickly grew in its wake
• Dynamic equilibrium hypothesis species
  diversity depends on the effect of disturbance on
  the competitive interactions of populations.

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Figure 53.16 Routine disturbance in a grassland
community
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Figure 53.18x2 Forest fire
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SUCCESSION

• Ecological succession transitions in species
  composition over time
• Primary succession when succession begins in an
  area that is virtually lifeless and has no soil.
• Lichens and mosses are usually the first
  macroscopic photosynthesizers
• Can slowly dissolve rock to make soil, which
  takes thousands of years

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Figure 53.18x1 Large-scale disturbance Mount
St. Helens
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Figure 53.19 A glacial retreat in southeastern
Alaska
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Table 53.2 The Pattern of Succession on Moraines
in Glacier Bay
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• Secondary succession occurs where an existing
  community has been cleared by some disturbance
  that leaves soil intact (example fire or
  volcanoes erupting)
• Typically pioneer species are r-selected (high
  birthrates and dispersal)

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Figure 53.18 Patchiness and recovery following a
large-scale disturbance
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ECOSYSTEMS

• Chapter 55

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FOOD WEBS and TROPHIC LEVELS

• Autotrophs
• Producers make own food
• Heterotrophs
• Primary consumers herbivores eat producers
• Secondary consumers carnivores eat primary
  consumers
• Tertiary consumers carnivores eat secondary
  consumers
• Detritivores (decomposers) eat detritus
  (nonliving organic material and dead remains)

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Figure 54.1 An overview of ecosystem dynamics
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A Food Web
Section 3-2
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Figure 54.2 Fungi decomposing a log
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• Production rate of incorporation of energy and
  materials into the bodies of organisms
• Consumption metabolic use
• Decomposition breakdown of organic material
  into inorganic

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ENERGY FLOW IN ECOSYSTEMS

• Most solar radiation is absorbed, reflected, or
  scattered in the atmosphere of Earth.
• Only a very small portion of sunlight is used by
  algae, bacteria, and plants for photosynthesis

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• Primary productivity amount of light energy
  converted to chemical energy by autotrophs in an
  ecosystem in a given time period
• Gross primary productivity (GPP) total primary
  productivity (not all of this energy is stored in
  autotrophs because autotrophs use energy for
  respiration)
• Net primary productivity (NPP)
• NPP GPP R
• Where R the amount of energy used in respiration

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C6H12O6 6O2 6CO2 6H2O
Respiration
Photosynthesis

• Gross primary productivity results from
  photosynthesis
• Net primary productivity is the difference
  between the yield of photosynthesis and the
  consumption of fuel in respiration

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• Primary productivity
• J/m2/yr (energy measured per area per unit time)
• g/m2/yr (biomass added per area per unit time)
• Seasonal changes and available nutrients can
  limit primary productivity

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Figure 54.3 Primary production of different
ecosystems
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Figure 54.4 Regional annual net primary
production for Earth
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• Limiting nutrient the nutrient that must be
  added to increase primary productivity
• Example nitrogen or phosphorus are often
  limiting in aquatic systems (especially in the
  photic zone)
• Secondary productivity rate at which an
  ecosystems consumers convert chemical energy
  into their own new biomass

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Figure 54.9 Nutrient addition experiments in a
Hudson Bay salt marsh
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Figure 54.11 An idealized pyramid of net
production
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ECOLOGICAL PYRAMIDS

• Pyramid of productivity
• 10 rule - 10 of energy at one level transfers
  to next level
• Where does the energy go?

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Figure 54.10 Energy partitioning within a link
of the food chain
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• Pyramid of biomass standing crop biomass (total
  dry weight)
• Some aquatic systems show inverted pyramids
  because zooplankton consume phytoplankton quickly
• Productivity still upright

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Figure 54.12 Pyramids of biomass (standing crop)
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Figure 54.13 A pyramid of numbers
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NUTRIENT CYCLING

• Biogeochemical cycles involve both abiotic and
  biotic components

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Figure 54.16 The water cycle
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Figure 54.17 The carbon cycle
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CARBON CYCLE

• Carbon dioxide in atmosphere is lowest in summer
  in N. hemisphere and highest in winter. More
  plants in summer less CO2 in atmosphere
• Dissolved CO2 makes carbonic acid (H2CO3)

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• Increased burning of fossil fuels has increased
  CO2 levels, which leads to global warming.
• Carbon dioxide absorbs much of the reflected
  infrared radiation greenhouse effect.
• Without the greenhouse effect, temperature would
  be 18C.

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Figure 54.26 The increase in atmospheric carbon
dioxide and average temperatures from 1958 to
2000 (readings taken from Mauna Loa, Hawaii)
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Global Warming

• A number of studies predict CO2 will double by
  end of 21st century.
• Will cause a predicted 2ºC average global temp
  increase
• Historically, a 1.3 ºC would make world warmer
  than any time in past 100,000 years.
• Poles probably most affected and polar ice
  melting may change our coastlines!

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Figure 54.18 The nitrogen cycle
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NITROGEN CYCLE

• Plants cannot use N2 (gas).
• Nitrogen fixing bacteria convert nitrogen gas
  into a form of N that plants can use ammonium
  (NH4) or nitrate(NO3-).
• Nitrogen fixing bacteria can live in the soil or
  in plants called legumes (mutualism).
• Legumes include beans, alfalfa, and soy.
• Denitrifying bacteria convert nitrate back into
  nitrogen gas.
• Without nitrogen fixing bacteria, plants could
  not get the nitrogen they need and would die.
  All life on earth depends on these bacteria.

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Figure 54.19 The phosphorous cycle
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PHOSPHORUS CYCLE

• Phosphorus is often the limiting nutrient in
  lakes.
• Sewage and runoff provide excess phosphorus.
  This can cause eutrophication. This is when a
  lake develops a high productivity, which is
  supported by high rates of nutrient cycling.
  This leads to algal blooms, which can suffocate
  the lake.

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Figure 54.8 The experimental eutrophication of a
lake
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Figure 54.24 Weve changed our tune
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BIOLOGICAL MAGNIFICATION

• Nonbiodegradable substances become more
  concentrated in increasing, successive trophic
  levels.
• The biomass at any given level is produced from a
  much larger biomass ingested from the level
  below.
• Example DDT caused birds of prey to lay eggs
  with thin shells.

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Figure 54.25 Biological magnification of DDT in
a food chain
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Chlorinated Hydrocarbons

• Include DDT, agent orange, PCBs (polychlorinated
  biphenyls)
• They are persistent (i.e., they persist in the
  environment for several years)
• They are non-polar (i.e., water-hating)
• They bioaccumulate (i.e., they concentrate in the
  fat of organisms, and their concentration
  increases as one moves up the food chain)
• They are causing a toxic effect at low
  concentrations

122

• Agent Orange was a defoliant used during the
  Vietnam War. 
• Agent Orange is an herbicide that was used during
  the Vietnam War to strip the land of vegetation
  making it easier for the US troops to see the
  opposing forces and also to deplete their food
  supply.
• Dioxin is a very toxic chemical within Agent
  Orange. 
• Dioxin is believed to be the cause of so much
  damage and has been linked to many cancers and
  birth defects.

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Dioxin (part of Agent Orange)
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OZONE DEPLETION

• Ozone (O3) provides a protective barrier to UV
  light.
• Chlorofluorcarbons react with O3 and reduce it to
  O2, which makes holes in the layer.
• Largest hole over Antarctica.
• Chlorofluorcarbons come from refrigerants,
  propellants in aerosol cans, and in some
  manufacturing processes.

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Figure 54.27a Erosion of Earths ozone shield
The ozone hole over the Antarctic
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Figure 54.27b Erosion of Earths ozone shield
Thickness of the ozone layer