Ecosystems: What Are
They and How Do They
Work?
Chapter 3
Key Concepts

What is ecology?

Major components of ecosystems

Energy flow and matter cycles

Ecosystem studies
Importance of Insects
Ecological Services

Pollination

Pest control

Important roles in
biological community
Nature of Ecology

What is ecology?
Study of connections in nature

Organisms

Cells

Species

Microbes rule!
Benefits Include:
Decomposition, nutrient cycling, foods, water
purification, digestion, antibiotics
Nature of Ecology
Known
species
1,412,000
Other animals
281,000
Insects
751,000
Fungi
69,000
Prokaryotes
4,800
Species Total?
Estimated 3.6 - 100
million
Protists
57,700
Plants
248,400
Animation
Levels of organization interaction
Levels of
Organization
of Matter
See Fig. 3-4, p.42
Genetic Diversity in One Snail
Species
What Sustains Life on Earth?

Troposphere: Earth’s
surface to 17km up78% N, 21% O2

Stratosphere- 17 - 48 km
contains ozone layer

Hydrosphere

Lithosphere= crust & upper
mantle

Biosphere = Zone of Earth
where life is found
(skin of the apple)
* All parts are interconnected!
Fig. 3-2, p. 41
What Sustains Life on Earth?
Oceanic
crust
Continental
crust
Atmosphere
Vegetation
and animals
Soil
Rock
Biosphere
Lithosphere
Upper mantle
Asthenosphere
Lower mantle
Crust
Core
Mantle
Crust (soil
and rock)
Biosphere
(living and dead
organisms)
Lithosphere
Hydrosphere
(crust, top of upper mantle)
(water)
Atmosphere
(air)
Fig. 3-2, p. 41
Earth’s Life-Support Systems
(3 interconnected factors)

One way flow of highquality energy

Cycling of matter

Gravity- holds atmosphere,
enables movement of
chemicals through various
spheres
“Energy flows, nutrients cycle.”
Earth’s Life-Support Systems
“Energy flows, nutrients cycle.”
Biosphere
Carbon
cycle
Phosphorus
cycle
Nitrogen
cycle
Water
cycle
Oxygen
cycle
Heat in the environment
Heat
Heat
Heat
Flow of Solar Energy to and from
the Earth

Greenhouse gases
water vapor, CO2, NO, CH4 , O3

Greenhouse effectHeat trapped in the troposphere
to warm planet
without natural
greenhouse effect life
would not be possible.
See Fig. 3-3, p. 41
Flow of Solar Energy to and from
the Earth
Solar
radiation
Energy in = Energy out
Reflected by
atmosphere (34%)
UV radiation
Radiated by
atmosphere
as heat (66%)
Lower Stratosphere
(ozone layer)
Absorbed
by ozone
Visible
light
Troposphere
Greenhouse
effect
Heat
Absorbed
by the
earth
Heat radiated
by the earth
Fig. 3-3, p. 41
Animation
Sun to Earth animation
Why is the Earth so Favorable
for Life?

Liquid water

TemperaturePast 3.7 billion years average surface temp. = 50- 68 °F

Gravity

Atmosphere
Major Biomes
Average annual precipitation
100–125 cm (40–50 in.)
75–100 cm (30–40 in.)
50–75 cm (20–30 in.)
25–50 cm (10–20 in.)
below 25 cm (0–10 in.)
4,600 m (15,000 ft.)
3,000 m (10,000 ft.)
1,500 m (5,000 ft.)
Coastal mountain
ranges
Coastal chaparral
and scrub
Sierra Nevada
Mountains
Great American
Desert
Coniferous forest
Rocky
Mountains
Desert
Great
Plains
Coniferous forest
Mississippi
River Valley
Prairie grassland
Appalachian
Mountains
Deciduous forest
Major Components of Freshwater Ecosystems
Sun
Producers (rooted plants)
Producers (phytoplankton)
Primary consumers (zooplankton)
Secondary consumers (fish)
Tertiary
consumers
(turtles)
Dissolved
chemicals
Sediment
Decomposers (bacteria and fungi)
Major Components of a Field
Ecosystem
Oxygen (O2)
Sun
Producer
Carbon dioxide (CO2)
Primary consumer
(rabbit)
Falling leaves
Precipitation
and twigs
Secondary consumer
(fox)
Producers
Soil decomposers
Water
Soluble mineral nutrients
Fig. 3-5, p. 43
Animation
Matter recycling and energy flow animation
ABC’s of Ecology
(The study of how organisms interact with one another
& their non-living environment)
•A= Abiotic (Non-living)
•B= Biotic (Living)
•C= Cultural (Human Interactions)
Factors Limiting Population Growth

Limiting factor principleToo much or too little of any abiotic factor can limit or prevent growth of
population.

Limiting factors:
Excess water or water shortages for terrestrial organisms
Excess or lack of soil nutrients
Dissolved oxygen for aquatic organisms
Salinity for aquatic organisms
Range of Tolerance
Lower limit
of tolerance
Few
organisms
Abundance of organisms
Few
organisms
No
organisms
Population Size
No
organisms
Upper limit
of tolerance
Zone of
intolerance
Low
Zone of
physiological stress
Optimum range
Temperature
Zone of
Zone of
intolerance
physiological stress
High
Factors That Limit Population Growth

Range of tolerance:
range of abiotic conditions required for population to survive

Law of tolerance
“The existence, abundance and distribution of a species in an
ecosystem are determined by whether the levels of one or more
physical or chemical factors fall within the range tolerated by
that species.”
Consumers: Feeding and
Respiration

Decomposers (Fungi & Bacteria) - specialized consumers that
breakdown detritus (dead stuff) into inorganic nutrients that can be reused
by producers

Omnivores

Detritivores- Decomposers & detritus feeders

Aerobic respiration
glucose + oxygen = carbon dioxide + water + ENERGY
Detritivores
Detritus feeders
Decomposers
Decomposers convert
organic chemicals to
inorganic chemicals that
can be used by producers
Long-horned
beetle holes
Bark beetle
engraving
Carpenter
ant
galleries
Termite and
carpenter
ant
work
Dry rot fungus
Wood
reduced
to powder
Time progression
Mushroom
Powder broken down by decomposers
into plant nutrients in soil
Fig. 3-6, p. 44
Main Structural Components of
an Ecosystem
Heat
Abiotic chemicals
(carbon dioxide,
oxygen, nitrogen,
minerals)
Heat
Solar
energy
Heat
Producers
(plants)
Decomposers
bacteria, fungi)
Heat
Consumers
(herbivores,
carnivores)
Heat
Fig. 3-7, p. 45
Animation
Linked processes animation
Animation
The role of organisms in an ecosystem
Biodiversity
(4 Components)
Fig. 3-14, p. 45
Examples of Biodiversity
Model of a Food Chain
First Trophic
Level
Producers
(plants)
Heat
Second Trophic
Level
Third Trophic
Level
Fourth Trophic
Level
Primary
consumers
(herbivores)
Secondary
consumers
(carnivores)
Tertiary
consumers
(top carnivores)
Heat
Heat
Solar
energy
Heat Heat
Heat
Heat
Detritivores
decomposers and detritus feeders)
Heat
Fig. 3-8, p. 46
Food Web in the Antarctic
Humans
Sperm whale
Blue whale
Elephant
seal
Killer whale
Crabeater seal
Leopard
seal
Adélie
penguins
Petrel
Emperor
penguin
Fish
Squid
Carnivorous plankton
Herbivorous
zooplankton
Krill
Phytoplankton
Fig. 3-9, p. 46
Energy Flow in an Ecosystem

Biomass

Ecological efficiency=
% of usable energy transferred as biomass from one trophic
level to the next (2% - 40%)
10% Rule- assumes 10% ecological efficiency

Pyramid of energy flow
Pyramid of Energy Flow
Heat
Heat
Tertiary
consumers
(human)
Decomposers
Heat
10
Secondary
consumers
(perch)
100
1,000
10,000
Usable energy
available at
each tropic level
(in kilocalories)
Heat
Primary
consumers
(zooplankton)
Heat
Producers
(phytoplankton)
See Fig. 3-10,
p. 47
Biomass Productivity

Gross primary productivity (GPP)
rate at which producers in an ecosystem convert sun into food

Net primary productivity (NPP)=
GPP - Respiration

NPP and populations
NPP limits the number of consumers that can live on earth
Differences between GPP and NPP
Sun
Respiration
Gross primary
production
Growth and reproduction
Energy lost and
unavailable to
consumers
Net primary
production
(energy
available to
consumers)
Net Primary Productivity in Major
Life Zones and Ecosystems
Terrestrial Ecosystems
Swamps and marshes
Tropical rain forest
Temperate forest
Northern coniferous forest
(taiga)
Savanna
Agricultural land
Woodland and shrubland
Temperate grassland
Tundra (arctic and alpine)
Desert scrub
Extreme desert
Aquatic Ecosystems
Estuaries
Lakes and streams
Continental shelf
Open ocean
800
1,600
2,400
3,200
4,000
4,800
5,600
6,400
7,200
8,000
8,800 9,600
Average net primary productivity (kcal/m2/yr)
Fig. 3-11, p. 48
Matter Cycling in Ecosystems:
Biogeochemical Cycles

Hydrologic (water) cycle

Carbon cycle

Nitrogen cycle

Phosphorus cycle

Sulfur cycle
Simplified Hydrologic (Water) Cycle
Condensation
Rain clouds
Transpiration
Precipitation
Precipitation to land
Transpiration
from plants
Rapid
Surface
runoff (rapid)
Evaporation
Precipitation
Evaporation
From
Evaporation
ocean
From
Precipitation
ocean
to ocean
Surface
runoff
(rapid)
Infiltration and
percolation
Groundwater movement (slow)
Ocean storage
Human Interventions in the
Hydrologic Cycle
1.
Large withdraw of surface and ground waters
2.
Clearing vegetation / wetland destruction -  runoff,
3.
Pollution - addition of nutrients
 infiltration,  groundwater recharge,  flood risk,  soil
erosion & landslides
The Carbon Cycle (Marine)
Diffusion between
atmosphere and ocean
Carbon dioxide
dissolved in
ocean water
Combustion of fossil fuels
photosynthesis aerobic
respiration
Marine food webs
Producers, consumers,
decomposers, detritivores
incorporatio
death,
n into
sedimentation
sediments
uplifting over
geologic time
Marine sediments, including
formations with fossil fuels
sedimentation
The Carbon Cycle (Terrestrial)
Atmosphere
(most carbon is in carbon dioxide)
Combustion
of fossil
fuels
volcanic action
Terrestrial
rocks
weathering
Soil water
(dissolved carbon)
photosynthesis
aerobic
respiration
Land food webs
Producers,
consumers,
decomposers,
detritivores
combustion of
wood (for
clearing land;
or fuel)
deforestaion
death, burial, compaction over geologic time
leaching
, runoff
Peat,
fossil fuels
Human Interferences in the
Global Carbon Cycle
1. Clearing Vegetation
2. Burning Fossil Fuels
potential consequences?
High
projection
Low
projection
Fig. 3-26, p. 56
The Nitrogen Cycle
Gaseous Nitrogen (N2)
in Atmosphere
Nitrogen
Fixation
by industry
for agriculture
Fertilizers
uptake
by
autotrop
hs
Food Webs
on Land
excretion, death,
decomposition
Nitrogen Fixation
bacteria convert N2 to
ammonia (NH3); this
dissolves to form
ammonium (NH4+)
NH3, NH4+
in Soil
loss by
leaching
Nitrogenous Wastes,
Remains in Soil
uptake
by
autotrop
hs
NO3–
in Soil
Denitrification
by bacteria
Ammonification 2. Nitrification
bacteria, fungi convert the
bacteria convert NO2–
residues to NH3; this
to nitrate (NO3–)
dissolves to form NH4+
1. Nitrification
bacteria convert NH4+
to nitrite (NO2–)
NO2–
in Soil
loss by
leaching
Human Interferences in the
Global Nitrogen Cycle
1. Add nitric oxide (NO) to atmosphere - can
form acid rain
2. Add nitrous oxide N2O to atmosphere via
anaerobic decomposition & inorganic fertilizers
- greenhouse gas
3. Nitrate in inorganic fertilizers can leach thru
soil & contaminate groundwater
4. Release large quantities of N into troposphere
via habitat destruction
5. Upset aquatic ecosystems from excess nitrates
in ag. runoff & sewage- eutrophication
The Phosphorus Cycle
mining
Fertilizer
Guano
excretion
agriculture
uptake by
autotrophs
Marine
Food
Webs
uptake by
autotrophs
Dissolved
in Ocean
Water
leaching, runoff
death,
decomposition
sedimentation
weathering
weathering
settling out
Marine Sediments
Dissolved
in Soil Water,
Lakes, Rivers
uplifting over
geologic time
Rocks
Land
Food
Webs
Human Interventions in the
Phosphorus Cycle
1. Mining of phosphate rock
2. Clearing tropical forests reduces available
phosphate in tropical soils
3. Phosphates from runoff of animal wastes, sewage
& fertilizers disrupts aquatic ecosystems
- eutrophication
“Since 1900, human activities have increased the
natural rate of phosphorous release to
environment by about 3.7 fold”
The Sulfur Cycle
Water
Sulfur trioxide
Sulfuric acid
Oxygen
Sulfur dioxide
Ammonia
Acidic fog and precipitation
Ammonium sulfate
Hydrogen sulfide
Plants
Dimethyl sulfide
Volcano
Animals
Industries
Ocean
Sulfate salts
Metallic
Sulfide
deposits
Decaying matter
Sulfur
Hydrogen sulfide
How Do Ecologists Learn
about Ecosystems?

Field research

Remote sensing

Geographic information system (GIS)

Laboratory research

Systems analysis