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Ecology and Human Concerns
Chapter 25
Ecology
Study of interactions of organisms
with one another and with the
physical environment
Ecological Terms
• Habitat
• Succession
• Community
• Primary succession
• Niche
• Secondary succession
• Specialist species
• Generalist species
• Ecosystem
Simple
Ecosystem
Model
energy
input from
sun
PHOTOAUTOTROPHS
(plants, other producers)
nutrient
cycling
HETEROTROPHS
(consumers, decomposers)
energy output (mainly heat)
Nature of Ecosystems
Autotrophs
• Producers
Heterotrophs
Tropic Levels
1 - Producers
2 - Herbivores
• Consumers
3 - Primary carnivores
• Detritivores
4 - Secondary carnivores
• Decomposers
• Omnivores
Food Chain
MARSH
HAWK
• A straight-line
sequence of who
UPLAND
SANDPIPER
eats whom
• Simple food chains
GARTER SNAKE
are rare in nature
CUTWORM
Food
Web
Primary Productivity
• Gross primary productivity is
ecosystem’s total rate of photosynthesis
• Net primary productivity is rate at which
producers store energy in tissues in
excess of their aerobic respiration
Ecological Pyramids
• Producers form base
• Biomass pyramid
• Energy pyramid
Energy pyramid for Silver Springs
top carnivores
carnivores
herbivores
21
383
3,368
producers
20,810
decomposers/detritivores
5,060
Biogeochemical Cycle
• The flow of a nutrient from the
environment to living organisms and
back to the environment
• Main reservoir for the nutrient is in the
environment
Three Categories
• Hydrologic cycle
– Water
• Atmospheric cycles
– Nitrogen and carbon
• Sedimentary cycles
– Phosphorus and sulfur
Hydrologic Cycle
Atmosphere
wind-driven water vapor
40,000
evaporation
from ocean
425,000
precipitation
into ocean
385,000
precipitation
onto land
111,000
evaporation from
land plants
(evapotranspiration)
71,000
surface and
groundwater flow
40,000
Oceans
Land
Phosphorus Cycle
• Phosphorus is part of phospholipids and
all nucleotides
• It is the most prevalent limiting factor in
ecosystems
• Main reservoir is Earth’s crust; no
gaseous phase
Phosphorus Cycle
mining
excretion
FERTILIZER
GUANO
agriculture
uptake by
autotrophs
MARINE
FOOD
WEBS
weathering
DISSOLVED
IN OCEAN
WATER
uptake by
autotrophs
weathering
DISSOLVED IN
SOIL WATER,
LAKES, RIVERS
death,
decomposition
sedimentation
death,
decomposition
leaching, runoff
settling out
uplifting over
geologic time
MARINE SEDIMENTS
ROCKS
LAND
FOOD
WEBS
Human Effects
• In tropical countries, clearing lands for
agriculture may deplete phosphorus-
poor soils
• In developed countries, phosphorus
runoff is causing eutrophication of
waterways
Carbon Cycle
• Carbon moves through the atmosphere
and food webs on its way to and from
the ocean, sediments, and rocks
• Sediments and rocks are the main
reservoir
Carbon Cycle
diffusion
Atmosphere
Bicarbonate,
volcanic action
carbonate
Marine
food
TERRESTRIAL
webs ROCKS
Terrestrial
rocks
photosynthesis
Land food
webs
Soil water
Marine sediments
weathering
Peat, fossil
fuels
Carbon in Atmosphere
• Atmospheric carbon is mainly carbon
dioxide
• Carbon dioxide is added to
atmosphere
– Aerobic respiration, volcanic action,
burning fossil fuels
• Removed by photosynthesis
Greenhouse Effect
• Greenhouse gases impede the escape
of heat from Earth’s surface
Carbon Dioxide Increase
• Carbon dioxide levels fluctuate
seasonally
• The average level is steadily increasing
• Burning of fossil fuels and deforestation
are contributing to the increase
Other Greenhouse Gases
• CFCs - synthetic gases used in plastics
and refrigeration
• Methane - produced by termites and
bacteria
• Nitrous oxide - released by bacteria,
fertilizers, and animal wastes
Nitrogen Cycle
• Nitrogen is used in amino acids and
nucleic acids
• Main reservoir is nitrogen gas in the
atmosphere
Nitrogen Cycle
GASEOUS NITROGEN
(N2) IN ATMOSPHERE
NITROGEN
FIXATION
by industry for
agriculture
FOOD WEBS
ON LAND
FERTILIZERS
NITROGEN FIXATION
uptake by
autotrophs
excretion,
death,
decomposition
NITROGENOUS WASTES,
REMAINS IN SOIL
NH3-, NH4+
IN SOIL
AMMONIFICATION
loss by
leaching
1. NITRIFICATION
uptake by
autotrophs
NO3IN SOIL
2. NITRIFICATION
NO2IN SOIL
loss by
leaching
Biological Magnification
A nondegradable or slowly degradable
substance becomes more and more
concentrated in the tissues of
organisms at higher trophic levels
of a food web
Human Population Growth
• Population now exceeds 6 billion
• Rates of increase vary among countries
• Average annual increase is 1.26 percent
• Population continues to increase
exponentially
Side-Stepping Controls
• Expanded into new habitats
• Agriculture increased carrying capacity;
use of fossil fuels aided increase
• Hygiene and medicine lessened effects
of density-dependent controls
Limiting Factors
• Any essential resource that is in
short supply
• All limiting factors acting on a
population dictate sustainable
population size
Logistic Growth
• As size of the
population increases,
rate of reproduction
decreases
• When the population
reaches carrying
capacity, population
growth ceases
carrying
capacity
Time
Density-Dependent Controls
• Logistic-growth equation deals with
density-dependent controls
• Limiting factors become more
intense as population size increases
• Disease, competition, parasites,
toxic effects of waste products
Air Pollutants
• Carbon oxides
• Sulfur oxides
• Nitrogen oxides
• Volatile organic compounds
• Photochemical oxidants
• Suspended particles
Industrial Smog
• Gray-air smog
• Forms over cities that burn large
amounts of coal and heavy fuel oils;
mainly in developing countries
• Main components are sulfur oxides and
suspended particles
Photochemical Smog
• Brown-air smog
• Forms when sunlight interacts with
components from automobile exhaust
• Nitrogen oxides are the main culprits
• Hot days contribute to formation
Ozone Thinning
• In early spring and
summer, ozone
layer over
South
America
Antarctica thins
• Seasonal loss of
ozone is at highest
level ever recorded
Antarctica
Effect of Ozone Thinning
• Increased amount of UV radiation
reaches Earth’s surface
• UV damages DNA and negatively
affects human health
• UV also affects plants, lowers
primary productivity
Water Use and Scarcity
• Most of Earth’s water is too salty for
human consumption
• Desalinization is expensive and
requires large energy inputs
• Irrigation of crops is the main use
of freshwater
Negative Effects of Irrigation
• Salinization, mineral buildup in soil
• Elevation of the water table and
waterlogging
• Depletion of aquifers
Generating Garbage
• Developed countries generate huge
amounts of waste
• Paper products account for half the
total volume
• Recycling can reduce pollutants, save
energy, ease pressure on landfills
Desertification
• Conversion of large tracts of grassland
to desertlike conditions
• Conversions of cropland that result in
more than 10 percent decline in
productivity
Effects of Deforestation
• Increased leaching and soil erosion
• Increased flooding and
sedimentation of downstream rivers
• Regional precipitation declines
• Possible amplification of the
greenhouse effect
Regions of Deforestation
• Rates of forest loss are greatest in
Brazil, Indonesia, Mexico, and Columbia
• Highly mechanized logging is
proceeding in temperate forests of the
United States and Canada
Reversing Deforestation
• Coalition of groups dedicated to saving
Brazil’s remaining forests
• Smokeless wood stoves have saved
firewood in India
• Kenyan women have planted millions
of trees
Fossil Fuels
• Coal, oil, natural gas
• Main energy source of developed
countries
• Burning of fossil fuels contributes to
global warming
Nuclear Energy
• Used extensively in some energypoor developed countries
• Little support in the United States
• Emits fewer air pollutants than
burning coal, but creates radioactive
wastes
• Potential for meltdown
Chernobyl Accident - 1986
• Core meltdown at a nuclear power plant
in the Ukraine
• 31 immediate deaths, radiation sickness
and death for others
• Cloud of radiation spread by winds
across Europe
• Long-term health impacts downwind
Wind Energy
• An indirect use of solar energy
• Wind farms are arrays of turbines
• Can supplement needs of some
regions but is not dependable
enough on its own
Solar-Hydrogen Energy
• Photovoltaic cells use sunlight
energy to split water
• Hydrogen gas produced in this way
can be used as fuel or to generate
electricity
• Clean, renewable technology
Deforestation
• Removal of all trees from large tracts
of land
• 38 million acres logged each year
• Wood is used for fuel, lumber
• Land is cleared for grazing or crops