AP Environmental Science
Ecology, Ecosystems,
& Food Webs
© Brooks/Cole Publishing Company / ITP
1. Ecology & Life
Ecology- study of relationships between organisms & their
environment.
Levels of organization of life:
organism
population
community
ecosystem
biome
biosphere
increasing size
Organisms
Organism- any form of life.
Species- organisms that resemble
each other and can potentially
interbreed.
•Estimated 5 to 100 million
species, most are insects &
microorganisms
•1.8 million named
• Each species is the result of
long evolutionary history.
•Native species- population that
exists in its natural habitat
•Non-native or introduced
species- population introduced
by humans.
Populations
Population- individuals of the same species in a
given area
-Examples: sunfish in a pond, white oak trees in a
forest, people in a city
• Habitat- the place where a population usually lives.
• Genetic diversity- in natural populations individuals
vary in their genetic makeup.
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Communities
Community- populations of all
species living together in a given
area.
• It is a complex interacting
network of plants, animals and
microorganisms.
• Example: redwood forest
community, consisting of
populations of redwoods & other
trees, shrubs and herbaceous
species, animals and
microorganisms.
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Ecosystems & Ecosphere
Ecosystem- a community of
different species interacting with
one another & with their non–
living environment of matter &
energy.
-Examples:
Patch of woods, a lake or pond, a
farm field, an entire watershed in
a tropical rain forest.
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Major Components of Ecosystems
Abiotic- non–living components
examples: water, air, nutrients, & solar energy
Biotic- living components (=biota)
examples: plants, animals, & microorganisms
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What is Life?
Characteristics of Life:
Organisms composed of cells that
contain genetic material
Organisms capture & transform matter
& energy from their environment to
supply needs for growth, survival, &
reproduction
Organisms maintain stable internal
conditions through homeostasis
Organisms capable of reproduction
Organisms adapt to changes in
environmental conditions through
evolution.
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2. Earth's Life–Support Systems
Earth's major components:
Atmosphere- troposphere +
stratosphere
Hydrosphere- all Earth’s water
Lithosphere- crust and upper
mantle; contains fossil fuels
and renewable soil chemicals
Biosphere- where living things
reside; consists of most of
hydrosphere, parts of lower
atmosphere and upper
lithosphere
The Earth contains several
spherical layers

CrustOutermost,
thin silicate zone, eight
elements make up 98.5% of the
weight of the earth’s crust

MantleLargest
zone, rich with iron, silicon,
oxygen, and magnesium, very hot

Lithosphere

Crust and upper mantle
CoreInnermost
zone, mostly iron, solid
inner part, surrounded by a liquid
core of molten material
Inner Core is hotter than surface of
the Sun
Atmosphere
Atmosphere- thin envelope of air around the planet
 Troposphere
Up to 17 km above sea level, contains N (78%), O
(21%), and is where weather occurs
 Stratosphere
17-48 km above sea level and contains ozone (O3) to
filter out most of the sun’s UV radiation
What Sustains
Life on Earth?
Life on the earth depends on
three interconnected factors



One-way flow of high-quality
energy from the sun (**only 0.1%
used for photosynthesis!)
Cycling of matter or nutrients
through all parts of the ecosphere
Gravity-allows the planet to hold
onto its atmosphere and causes
the downward movement of
chemicals in the matter cycles
Energy Flow & Nutrient Cycling
Life on Earth depends upon
one–way flow of high–
quality energy from sun &
cycling of crucial elements.
**Earth is an open system in
regards to energy, and a
closed system in regards to
matter
What about living things?
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Nutrient Cycles
Nutrient- any atom, ion, or molecule an
organism needs to live, grow, or reproduce.
• Macronutrients needed in large amounts
e.g., C, O, H, N, P, S, K, Ca, Mg, Fe
• Micronutrients needed in small amounts
e.g., Na, Zn, Cu, Cl, I
• Nutrient cycles (biogeochemical cycles)- flow of
nutrients from nonliving (air, water, soil, rock) to
living organisms (biota) & back again.
•Driven directly or indirectly by solar
radiation & gravity.
•Major cycles: hydrologic (water), carbon,
oxygen, nitrogen, phosphorus and sulfur.
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Major Components of Ecosystems
Major components of aquatic ecosystems.
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Limiting Factors
Law of tolerance- a species’ livelihood in an
ecosystem is determined by the levels of 1 or
more physical or chemical factors falling w/in
the range tolerated by that species.
•Limiting factor- regulates survival,
growth, or reproduction.
•Limiting factor principle-too much or little
of any abiotic factor can limit or prevent
growth of a population, even if all other
factors are at or near the optimum range
of tolerance.
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Range of Tolerance
There is a range of tolerance for temperatures that fish
can live in.
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Major Living Components
Two main categories:
1) Producers (autotrophs)•
•
Photosynthetic: make their own energy
source through photosynthesis
****Only 0.1% of sun’s energy gets
used for this****
Chemosynthetic: convert simple
compounds into complex nutrients
w/o sunlight, e.g., bacteria of thermal
vents use H2S & CO2.
2) Consumers (heterotrophs)•
•
Get energy & nutrients by feeding on other
organisms or their remains.
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Includes herbivores, carnivores, decomposers,
etc.
Photosynthesis & Respiration
Photosynthesis- solar radiation is captured by chlorophyll (& other
pigments)
carbon dioxide + water + solar energy  glucose + oxygen
6 CO2
+
6 H2O + solar energy 
C6H12O6 +
O2
Aerobic respiration- organic molecules (e.g., glucose) are used for an
energy source
glucose + oxygen 
C6H12O6 + O2

carbon dioxide + water + energy
6 CO2
+ 6 H2O + energy
**TRANSFER OF CARBON BETWEEN ORGANISMS WITH THESE TWO
PROCESSES!!
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Consumers
Consumers (= heterotrophs)
• Primary consumers- (herbivores) feed directly on producers
• Secondary consumers- (carnivores) feed on primary
consumers
• Tertiary consumers- feed only on carnivores
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Other Feeders
•Omnivores- consumers that feed on both plants & animals
•Scavengers- feed on dead organisms
•Detritivores- feed on detritus (partially decomposed organic matter,
such as leaf litter & animal dung)
•Decomposers- consumers that complete the breakdown & recycling
of organic materials from the remains & wastes of other organisms
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4. Food Webs & Energy Flow
Food chains involve a sequence of organisms, each of
which is the food for the next.
**ARROW DIRECTION SHOWS FLOW OF ENERGY!!!
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Food Webs
& Energy
Flow
Example of some of
the complexity of a
food web in
Antarctica.
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Energy Pyramids
As energy flows through trophic levels there is a conversion
of usable energy to heat—2nd law of thermodynamics
Rarely have more than 4 steps
Ecological efficiency- percentage of USABLE energy
transferred from one trophic level to anothertypically 10%
Shown by pyramid of energy





10,000,000 units of energy from sun
10,000 units used by green
plants (photosynthesis-0.1%)
1000 units for herbivores
100 units for primary carnivores
10 units for secondary carnivores
Biomass
Biomass- dry weight of all
organic matter contained
in organisms.



Water is not source of
energy or nutrients
Biomass of first trophic
levels is dry mass of all
producers
Useable energy transferred
as biomass (eaten)
Biomass Pyramids
Biomass pyramids (dry mass)- show the biomass
available at every level and can look like the energy
pyramid (as for the abandoned field) or be inverted (as
for the ocean).
Inverted biomass pyramids result because the majority
of short-lived producers are eaten by larger, long-lived
consumers.
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Pyramids of Numbers
Pyramids of numbers- show the number of organisms
at each trophic level.
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Primary Productivity
•Gross primary productivity (GPP)- rate at which an ecosystem's
producers convert solar energy into chemical energy as biomass.
•Net primary productivity (NPP)- rate at which energy for use by
consumers is stored in new biomass (plant growth)
NPP = GPP – [rate at which producers use biomass]
OR
Biomass growth available to consumers = GPP – plant aerobic respiration
***Planet’s NPP (energy output of producers) ultimately limits the
number of consumers that can survive on earth.
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Sun
Respiration
Gross primary
production
Energy lost &
unavailable to
consumers
Net primary
production
Growth and reproduction (energy
available to
consumers)
Primary Productivity
Estimated annual net primary productivity of major biomes & aquatic
life zones, expressed as kilocalories per square meter per year.
**THIS FIGURE GIVE THE AVERAGE NPP PER UNIT AREA
SO IT IS A MEASURE OF AN AREA’S NPP EFFICIENCY!!
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5. Matter Cycling in Ecosystems
Nutrient (biogeochemical)
cycles- Natural processes
that recycle nutrients from
the nonliving environment
to living organisms and
back again
 Water, Carbon,
Nitrogen, Sulfur,
Phosphorus, etc.
Hydrologic Cycle
Carbon Cycle
CO2 is an important temperature regulator on earth
(greenhouse gas)
 Combustion of fossil fuels release CO2
 Carbon cycles through the ocean, which releases more
carbon dioxide with warmer temps
CH4 (methane)-principle component of natural gas and gases
released from bacterial decomposition of waste in landfills.
Largest reservoirs of carbon?
1. carbonate rocks
2. oceans
Carbon Cycle Animation
Carbon Cycle
Ways in which we’re interfering:
 Burning fossil fuels
 Destruction of
photosynthesizing vegetation
has contributed to global
warming
 The natural greenhouse effect
is strengthened by warmer
temps (more CO2 released from
warmer ocean)—positive
feedback
 Excessive waste in landfills and
global warming releasing more
methane clathrates.
 Methane clathrate video
Nitrogen Cycle
Ways in which we’re interfering:






Nitric oxide released from burning fuel
which produces nitric acid.
NONO2 HNO3 (nitric acid rain)
Nitrous oxide (N2O) released by bacteria
acting on livestock wastes and fertilizers
which warms atmosphere and depletes
ozone
Destruction of forests, grasslands, and
wetlands releases N into air
Pollution of aquatic systems with
agricultural runoff and human sewage
Harvesting crops removes N
Increased N in air, soil, water affecting
biodiversity
Sulfur Cycle
Much is stored in rocks
Burning coal, refining oil and
producing some metals from
ores (smelting) all add sulfur to
environment (SO2 gas)
These are converted to sulfuric
acid H2SO4 (acid rain)
DMS (dimethyl sulfide) released
by algae and diffuses from
oceans and can form sulfate
particles, which causes cloud
formation and possible
regulation of climate
Phosphorus Cycle
Important element in DNA, RNA,
ATP.
Very slow because no gaseous
state!
Found in soil, organisms, marine
sediment, rock, and guano (bird
and bat poop.)
Limiting factor for plant growth so
used in some fertilizers
Limits growth of producers in
freshwater streams and lakes due
to low solubility (ability to dissolve)
Phosphorus Cycle Animation
Phosphorus Cycle
Ways in which we interfere
 Mine phosphate rock to make
fertilizers and detergents
 Cut down tropical forests and reduce
the phosphorus in tropical soils
 Compromise aquatic systems with
animal waste runoff and human
sewage.
 Leads to overgrowth of algae, which
when decomposed leads to lowering
of DO for aquatic life.
 Banned in soaps and detergents in
some states, EU, Japan, and
Canada
7. Ecosystem Services &
Sustainability
Ecosystem services- natural benefits that support life
on the earth & are essential to the quality of human
life & the functioning of the world's economies.
Examples:
• control & moderate climate
• recycle vital nutrients
• provide energy & mineral resources
• furnish food, fiber, medicine, timber, & paper
• pollinate crops & useful native plants
• absorb, dilute, or detoxify pollutants
• control populations of pests & disease organisms
• slow soil erosion & prevent flooding
• provide biodiversity of genes & species
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Two Principles of Ecosystem
Sustainability
Use renewable solar energy
as energy source
Efficiently recycle nutrients
organisms need for survival,
growth, and reproduction
Greenhouse gases in
Troposphere
Water vapor
Carbon dioxide
Methane (CH4)
Nitrous oxide (N2O)
Ozone (O3)—major layer in
stratosphere, dangerous in
troposphere
These warm atmosphere due to
absorption of sun’s radiation and
release of longer wavelength,
infrared radiation.