Transcript Chapter 3

Chapter 3
Ecosystems: What are they and how do
they work?
Ecology



“Study of how organisms interact with one
another and with their nonliving
environment”
“Connections in nature”
Ecology focuses on: organisms, populations,
communities, ecosystems, and biosphere
Perspective
Small scale

Organism: any form of life


Multi-celled and single-celled
Species: “groups of organisms that resemble one
another in appearance, behavior, chemistry, and
genetic makeup”


1.4 million named/identified species
Probably 4-100 million total species
Large scale

Population: “a group of interacting individuals of the
same species occupying a specific area”





Community: all populations of different species in
the same area
Ecosystem: where populations interact with their
living and non-living environment


Genetic diversity – variations in genetic makeup
Habitat – where the population lives
Distribution / range: area the species covers
Natural or artificial
Biosphere: all of earth’s ecosystems
(all life on earth)
THE EARTH’S LIFE SUPPORT
SYSTEMS

The biosphere
consists of several
physical layers that
contain:





Air
Water
Soil
Minerals
Life
Figure 3-6
Earth’s spheres

Atmosphere: air around earth



Hydrosphere: all of earth’s water





Troposphere: inner layer of atmosphere – most
air is here (78% nitrogen, 21% oxygen)
Stratosphere: upper layer of atmosphere –
contains ozone
Liquid water
Ice
Water vapor
Lithosphere: earth’s crust and
upper mantle
Biosphere: all life on earth
Life sustaining processes

Flow of energy





Sun and other organisms (feeding) go in as highquality energy
Continue flow as low-quality energy
Back to space as heat
Cycling of matter: C, N, P cycles
Gravity
The sun!








Sun  earth (through electromagnetic waves)
Plants/bacteria take in energy to make food 
other organisms eat photosynthetic organisms
Energy from the sun drives other systems on
earth, like weather and water
1/1x109 of the sun’s energy makes it to earth
Most of the E is reflected back
80% warms troposphere and
cycles water
1% generates wind
<0.1% is used for photosynthesis
What Happens to Solar Energy
Reaching the Earth?

Solar energy
flowing through
the biosphere
warms the
atmosphere,
evaporates and
recycles water,
generates winds
and supports
plant growth.
Figure 3-8
Greenhouse gasses





H2O, CO2, CH4, N2O, O3
Larger-wavelength light waves are absorbed and
re-emitted by these molecules, heating them up
Natural greenhouse effect keeps us warm (moon
is 107 C in the day, -153 C at night)
Ozone keeps some harmful UV rays away
Human-produced greenhouse gasses add to the
effect
Biomes and aquatic life zones

Biomes: “large regions… with distinct
climates and specific species (especially
vegetation) adapted to them”


Forests, deserts, grasslands, tundra, etc
Aquatic life zones: watery parts of the
biosphere


Freshwater life zones
Ocean/marine life zones
Components of ecosystems


Abiotic: nonliving components – air, water,
nutrients, solar E
Biotic: consists of living components




Producers: photosynthetic plants and bacteria
Consumers: eat producers/other consumers
Decomposers: break down dead organisms
Range of tolerance: extremities of the
conditions that a population can live

Members within a population will have
variation in range of tolerance
Limits to population growth





Limiting factor: what is holding something back
Limiting factor principle: “too much or too 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”
Precipitation
Nutrients
Temperature

Factors That Limit Population
Growth
Availability of matter and energy resources can
limit the number of organisms in a population.
Figure 3-11
Producers!

Producers = autotrophs







Photoautotroph
Chemoautotroph
Make their own food
Land = plants (mostly)
Water = phytoplankton (mostly)
Photosynthesis: CO2 + H2O  C6H12O6 + O2
Chemosynthesis: make food from chemical E
(bacteria near hydrothermal vents use H2S)
Photosynthesis:
A Closer Look


Chlorophyll molecules in the
chloroplasts of plant cells
absorb solar energy.
This initiates a complex series
of chemical reactions in which
carbon dioxide and water are
converted to sugars and
oxygen.
Figure 3-A
Consumers





Heterotrophs: get energy from other organisms
Primary: herbivores; directly eat producers
Secondary: eat primary consumers
Third and further level: eat secondary or higher
consumers
Omnivores: eat plants and animals
Decomposers




Passively “eat” dead organic matter
Dentritivores: “insects and other scavengers
that feed on the wastes or dead bodies of
other organisms”
Very important to our ecosystem
Examples:



Bacteria
Fungi
Worms
Aerobic and anaerobic respiration




Aerobic respiration: oxygen burns organic
nutrients into CO2 and H2O
C6H12O6 + 6O2  6CO2 + 6H2O + E
Anaerobic respiration: breaking down organic
compounds without oxygen; fermentation
Instead of CO2 and H2O, end results are methane,
ethyl alcohol, acetic acid, and hydrogen sulfide
Two Secrets of Survival: Energy
Flow and Matter Recycle

An ecosystem
survives by a
combination of
energy flow and
matter recycling.
Figure 3-14
Biodiversity


Biodiversity: “renewable resource”
Four components:




Functional diversity – bio and chem processes
Ecological diversity – variety of ecosystems
Genetic diversity – variety of genetic material in a
species/population
Species diversity – variety of species in different
habitats
Biodiversity loss








HIPPO!!!
Habitat destruction and degradation
Invasive species
Pollution
Population growth (human)
Overexploitation (overhunting, overconsumption)
Why care?
Two approaches:


Ecosystem approach – protect populations of species in
their natural habitats
Species approach – protect species from premature
exticntion
The Ecosystem Approach
Goal
Protect populations of
species in their
natural habitats
Strategy
Preserve sufficient
areas of habitats in
different biomes and
aquatic systems
Tactics
•Protect habitat areas
through private
purchase or
government action
•Eliminate or reduce
populations of
nonnative species
from protected areas
•Manage protected
areas to sustain
native species
•Restore degraded
ecosystems
The Species Approach
Goal
Protect species
from premature
extinction
Strategies
•Identify endangered
species
•Protect their critical
habitats
Tactics
•Legally protect
endangered species
•Manage habitat
•Propagate
endangered
species in captivity
•Reintroduce species
into
suitable habitats
Fig. 3-16, p. 63
Energy flow in ecosystems

Little matter is wasted in ecosystems








Food chain – energy and nutrients move through
an ecosystem
Trophic level: where a species falls on a food web
Food web – shows more connections than chain,
relations between species
First Trophic
Level
Second Trophic
Level
Third Trophic
Level
Producers
(plants)
Primary
consumers
(herbivores)
Secondary
consumers
(carnivores)
Heat
Heat
Fourth Trophic
Level
Tertiary
consumers
(top carnivores)
Heat
Solar
energy
Heat Heat
Heat
Heat
Heat
Detritivores
(decomposers and detritus feeders)
Fig. 3-17, p. 64
Humans
Blue whale
Sperm whale
Crabeater
seal
Elephant
seal
Killer whale
Leopard
seal
Adelie
penguins
Emperor
penguin
Petrel
Fish
Squid
Carnivorous plankton
Krill
Phytoplankton
Herbivorous
plankton
Fig. 3-18, p. 65
Energy flow



Biomass – dry weight of all organic matter in
organisms of a food chain/web
Each time E is transferred, heat energy is lost
Ecologic efficiency – usually about 10%, can be
between 2% and 40%
Heat
Tertiary
consumers
(human)
Heat
Decomposers
Heat
10
Secondary
consumers
(perch)
Heat
100
1,000
Primary
consumers
(zooplankton)
Heat
10,000
Producers
Usable energy (phytoplankton)
Available at
Each tropic level
(in kilocalories)
Fig. 3-19, p. 66
Productivity






Gross primary productivity (GPP) – “the rate at which an
ecosystem’s producers convert solar energy into chemical
energy”
Net primary productivity (NPP) – “the rate at which
producers use photosynthesis to store energy minus the
rate at which they use some of this stored energy”
NPP = GPP – R (energy used in respiration)
NPP limits number of consumers
Humans use/waste/destroy 27% of earth’s potential NPP
Humans, pets, and livestock make up 98% of earth’s
vertebrate biomass
Gross primary productivity
(grams of carbon per square meter)
Fig. 3-20, p. 66
Sun
Respiration
Gross primary
production
Growth and reproduction
Energy lost
and unavailable
to consumers
Net primary
production
(energy
available to
consumers)
Fig. 3-21, p. 66

What are nature’s three most productive and
three least productive systems?
Figure 3-22
Soil





Soil – eroded rock, mineral nutrients, decaying
organic matter, water, air, and organisms
Weathering – rock breaking down into fragments
and particles by physical, chemical, and biological
processes
Support for plants and other life, filters water,
and helps remove CO2
Humans have accelerated natural soil erosion
1/3 to 1/2 of world’s croplands are losing topsoil
faster than it’s being renewed naturally
Soil layers








“Soil horizons”
Soil profile 
O horizon – organic material
A horizon – “humus” = partially
decomposed plants and animals
B and C horizon – inorganic material
Pores contain air and water
Infiltration – water moving down
through the soil
Leaching – water dissolves minerals
and organic matter and seeps down
in the soil
Oak tree
Fern
O horizon
Leaf litter
Wood
sorrel
Lords and
ladies
Dog violet
Grasses and
small shrubs
Earthworm
Millipede
Honey
fungus
Mole
Organic debris
builds up
Rock
fragments
Moss and
lichen
A horizon
Topsoil
B horizon
Subsoil
Bedrock
Immature soil
Regolith
Young soil
Pseudoscorpion
C horizon
Mite
Parent
material
Nematode
Root system
Mature soil
Red Earth
Mite
Springtail
Actinomycetes
Fungus
Bacteria
Fig. 3-23, p. 68
Some Soil Properties

Soils vary in the size
of the particles they
contain, the amount
of space between
these particles, and
how rapidly water
flows through them.
Figure 3-25
Soil properties





Soil texture
Clay particles = small
Silt particles = medium
Sand particles = large
Loam = mix of all three, best for growing plants
Soil Profiles of the
Principal Terrestrial
Soil Types
Figure 3-24
Matter cycling



Nutrients – “elements and compounds that
organisms need to live, grow, and reproduce”
Biogeochemical cycles aka nutrient cycles
Driven by solar E and gravity
Water cycle




AKA hydrologic cycle
Powered by gravity and E from sun
About 84% water vapor from oceans
Where does the water go?







Glaciers
Aquifers
Surface runoff – streams  lakes  oceans
Runoff causes natural erosion
Carries nutrients in/between ecosystems
Water is naturally purified in the water cycle
Cycle of natural renewal of water quality
Water’ Unique Properties






There are strong forces of attraction between
molecules of water.
Water exists as a liquid over a wide
temperature range.
Liquid water changes temperature slowly.
It takes a large amount of energy for water to
evaporate.
Liquid water can dissolve a variety of
compounds.
Water expands when it freezes.
Effects of humans on the water cycle


Withdraw large amounts of freshwater from rivers,
lakes, and underground, sometimes faster than it is
replaced
Clearing land / destroying wetland





Increases runoff – more chemicals and erosion
Reduces ability to refill groundwater supplies
Increases potential to flood
Adding nutrients and pollutants
Warmer climate (global warming) is causing the
water cycle to speed up


Change weather patterns
Intensify global warming
Carbon cycle




Based on CO2
CO2 helps regulate temperature on earth
Producers remove CO2, consumers put it back into
the cycle
Long-term carbon sinks



Oil deposits
Marine shells
Human effects


Clear more vegetation than can grow back, which reduces
the CO2 taken out of the atmosphere
Burn oil/wood which puts more CO2 into the atmosphere
Effects of Human Activities
on Carbon Cycle

We alter the carbon
cycle by adding
excess CO2 to the
atmosphere
through:


Burning fossil fuels.
Clearing vegetation
faster than it is
replaced.
Figure 3-28
Nitrogen cycle





N is an important element to some organic
molecules (nucleic acids and amino acids)
Nitrogen is “fixed” by bacteria (or lightning),
turning N2 into NH3 (plants can take up NH4+)
NH3 can be turned into NO2- (harmful to plants)
into NO3- (helpful to plants) by other bacteria
Decomposers convert N in organic compounds
back into NH3
Yet more bacteria can turn NH3 back into N2 or
N2 O
Effects of humans on the nitrogen cycle






Add large amounts of NO into atmosphere when we
burn fuels at high temps, which can turn into NO2,
which can turn into HNO3 (acidic)
Livestock and fertilizer adds N2O to the atmosphere
(bacteria breaking down waste) which can deplete
ozone or warm atmosphere
NO3- from fertilizers can contaminate ground water
Destroying plants releases more N into the
atmosphere
Agricultural and sewage runoff changes nitrate levels
in aquatic ecosystems
Harvesting or irrigating N-rich crops remove N from
soil
Phosphorus cycle






Phosphorus needed in DNA and ATP
Slow cycle, little P circulates in atmosphere, flows
mostly from land into oceans
P is typically found in salts (with PO43-) in rocks
PO43- from rocks wash into oceans, get deposited as
sediment, and will show up millions of years later as
rocks shift back to surface
Plants get PO43- from soil (usually a limiting growth
factor) and we get P from plants, and waste P leaves
us in urine
PO43--salts are not very soluble in water, so aquatic
plant life is limited by P levels
Effect of humans on phosphorus cycle



Mining for PO43- for fertilizers removes large
quantities in a short period
Destruction of tropical forests decreases amount
of PO43- available in tropical soil
PO43- runoff from fertilizers, livestock, and
sewage disrupts aquatic systems
Sulfur cycle







A lot of sulfur is in rocks underground or in (SO42-) salts
under ocean sediments
H2S (toxic) released form volcanoes (as is SO2) and some
organic matter broken down by decomposers
SO42- can enter the atmosphere from sea spray, dust
storms, and forest fires
Plants absorb SO42- from the soil to use for some proteins
Some marine algae produce CH3SCH3 which can form the
starting points for cloud condensation
SO2 and SO3 in the air can make H2SO4 (acidic)
In anaerobic environments, SO42- can be converted to S2where it can react with metals to be deposited as rock
Effects of humans on the sulfur cycle

3 ways we release sulfur into the atmosphere



Burning coal and oil that contains sulfur
Refining petroleum containing sulfur
Converting metallic mineral ores that contain sulfur
into free metal
Gaia hypothesis






The earth is very complex, with many different
systems working together in intricate ways
Does earth behave like a living thing?
Strong Gaia hypothesis – life controls the earth’s
life-sustaining processes
Not widely supported
Weak Gaia hypothesis – life influences the earth’s
life-sustaining processes
Widely supported
HOW DO ECOLOGISTS LEARN ABOUT
ECOSYSTEMS?

Ecologist go into ecosystems to observe, but
also use remote sensors on aircraft and
satellites to collect data and analyze
geographic data in large databases.



Geographic Information Systems
Remote Sensing
Ecologists also use controlled indoor and
outdoor chambers to study ecosystems
Geographic Information Systems (GIS)


A GIS organizes,
stores, and analyzes
complex data
collected over broad
geographic areas.
Allows the
simultaneous overlay
of many layers of
data.
Figure 3-33
Systems Analysis

Ecologists develop
mathematical and
other models to
simulate the
behavior of
ecosystems.
Figure 3-34
Importance of Baseline
Ecological Data

We need baseline data on the world’s
ecosystems so we can see how they are
changing and develop effective strategies for
preventing or slowing their degradation.

Scientists have less than half of the basic ecological
data needed to evaluate the status of ecosystems in
the United Sates (Heinz Foundation 2002;
Millennium Assessment 2005).