36.1 Feeding relationships
determine the path of energy
and chemicals in the
ecosystem
I. Energy Flow and Chemical
Cycling
A. Energy enters an ecosystem as light.
B. Photosynthetic producers, like plants,
change light energy to chemical energy
(organic compounds).
C. Consumers obtain chemical energy by
feeding on producers or on other
consumers.
D. Decomposers break down wastes and
dead organisms.
E. As living things use chemical energy,
they release heat/thermal energy.
F. Energy is not recycled within an
ecosystem, but flows through it and
out. (light energy into chemical energy
into heat energy)
G. Chemicals, such as C, O, & N, can be
recycled between living & nonliving
parts of ecosystems & the biosphere
II. Food Chains
A. A food chain is a pathway of food
transfer from one trophic level (feeding
level) to another (see Figure 36-2).
B. Producers make up the trophic level
that supports all others.
C. Consumers are the organisms in
trophic levels above producers.
D. Consumers can be categorized by
what they eat:
1. Herbivores eat only producers. (i.e.
cow eats grass)
2. Carnivores eat only other consumers.
(i.e. lion eats zebra)
3. Omnivores eat both consumers and
producers. (i.e. bear eats salmon &
berries)
E. Consumers can be categorized by position in
a food chain.
1. Primary consumers feed directly on
producers (i.e.grasshoppers eating plants)
2. Secondary consumers eat primary
consumers. (i.e. mice eating grasshoppers);
Tertiary eat secondary…
F. Decomposers feed on & break down detritus
(wastes & remains of dead organisms).
1. The main decomposers are bacteria and
fungi; they’re abundant in soil.
2. All ecosystems include decomposers even
though most food chains don’t show
decomposers.
III. Food Webs
A. Feeding relationships are usually
more complicated than shown in
simple food chains.
B. Ecosystems contain many different
species that have a variety of food
sources.
C. Food webs show the feeding
relationships between interconnected
& branching food chains
A Desert Food Web
36.2 Energy flows through
ecosystems
I. Productivity of Ecosystems
A. Available energy or energy budget is
limited in an ecosystem.
B. For most ecosystems, the amount of
sunlight that enters the ecosystem
determines the budget.
C. Earth’s producers make billions of
kilograms of organic material, or
biomass, each year.
Productivity
D. The rate at which producers build
biomass is called primary productivity.
E. Primary productivity determines the
maximum amount of energy available
to all the higher trophic levels in an
ecosystem.
Productivity
F. Productivity is different for different
ecosystems:
1. Tropical rainforests have the highest
productivity. Why? Their warm moist
climate supports year-round growing.
2. Productivity is low in typically dry & cold
Tundra.
3. Conditions are more moderate for
producers in grasslands
Productivity
Rain Forest
Grasslands
Tundra
Productivity
G. Exception – organisms living in deep
dark oceans do not get their energy
from the sun; prokaryotic producers can
extract energy from sulfur compounds
released by hydrothermal vents to make
organic compounds.
II. Ecological Pyramids
A. Energy is “spent” at each step of the
food web.
B. As each consumer feeds, some energy
is transferred from the lower trophic
level to the higher trophic level.
C. An average of 10% of the available
energy at a trophic level is converted to
biomass in the next higher trophic level.
D. The rest of the energy (about 90%) is
lost as heat.
E. The amount of energy available to top-level
consumers is tiny compared to that
available to primary consumers.
F. It takes a lot of vegetation to support higher
trophic levels.
G. Most food chains are limited to three or four
levels because there is not enough energy
at the top of the energy pyramid to support
another trophic level.
H. Ecological pyramids are diagrams used to
depict information about energy, biomass,
and numbers of organisms at different
trophic levels.
An Energy Pyramid
36.3 Chemicals cycle in
ecosystems
I. The Basic Pattern of
Chemical Cycling
A. Chemical cycles usually involve three
general steps:
1. Producers incorporate chemicals from the
nonliving environment into organic molecules.
2. Consumers feed on the producers,
incorporating some of the
chemicals into their own bodies and
releasing some back into the environment as
waste.
3. Organisms die & decomposers break
them down, supplying soil, water, & air
with chemicals in inorganic form. The
producers gain a renewed supply of raw
materials for building organic matter, &
the cycles continue.
B. Part of each chemical’s cycle involves
nonliving processes like rain and fires.
II. The Carbon and Oxygen
Cycle
A. Carbon is found in inorganic form in
the atmosphere as CO2 gas and
dissolved in water as HCO3- .
B. Producers use the carbon and
oxygen atoms to form organic
compounds during photosynthesis.
C. Some organic compounds cycle to
consumers as food.
Carbon-Oxygen Cycle
D. During cellular respiration producers &
consumers break down organic
compounds and release CO2 gas as a
waste product.
E. Decomposers break down detritus and
release CO2 gas.
F. Burning fossil fuels (coal, oil, natural gas)
& wood releases CO2 gas into the
atmosphere.
G. Volcanic eruptions add CO2 gas to
atmosphere.
Carbon-Oxygen Cycle
Forms organic
compounds during
photosynthesis
During cellular
respiration both
consumers and
producers release
carbon dioxide
Non-living processes –
burning fossil fuels, forest
fires and human activities
also release carbon dioxide
into the atmosphere
Decomposers break
down detrius –
releasing carbon
dioxide
III. The Nitrogen Cycle
A. Nitrogen is found in all living organisms in
amino acids & other essential molecules.
B. Almost 78% of Earth’s atmosphere is
nitrogen gas (N2).
C. Most producers can only use nitrogen in the
form of compounds like ammonium (NH4+)
and nitrate (NO3-).
D. Nitrogen-fixing bacteria convert N2 gas to
ammonia (NH3) in a process called nitrogen
fixation.
Nitrogen Cycle
E. Nitrogen-fixing bacteria live in soil and
in nodules on roots of plants (peas,
beans, alfalfa).
F. Other bacteria in soil convert NH4+ to
nitrates in a process called nitrification.
G. Producers absorb ammonium and
nitrates and use them to build amino
acids, proteins, and nucleic acids.
Nitrogen Cycle
H. Consumers that eat producers
obtain nitrogen.
I. Decomposers release nitrogen
(ammonium) from wastes and
decaying organisms.
J. Denitrifying bacteria in soil convert
some nitrates to N2 gas back into
atmosphere.
Nitrogen Cycle
Lives in soil and in
nodules on roots
Decomposers
release nitrogen from
wastes and decay
(as ammonium)
Producers absorb ammonium
and nitrates from the soil and
use them to build amino acids,
proteins and nucleic acids.
Consumers eat the producers –
obtaining nitrogen
Ammonia picks up
another hydrogen ion
from water to form
ammonium
Nitrification – other bacteria in the
soil converts ammonium into
nitrates
IV. Water Cycle
A. Sun’s energy evaporates water putting
water vapor into atmosphere.
B. Water vapor cools and condenses and falls
as precipitation.
C. Plants absorb fresh water from soil.
D. Consumers obtain water from eating and
drinking.
E. Water evaporates from the leaves of plants
= transpiration.
F. Some water runs off land into rivers and
streams and some restores groundwater.
Water Cycle
Falls as rain, snow, hail or
sleet
Evaporation
from the leaves
of plants
36.4 Human activities can
alter ecosystems
I. Human Activities Impact
Carbon Cycle
A. Deforestation – clearing forests for
agriculture, lumber, etc., affects carbon cycle
by eliminating the plants that remove CO2
from atmosphere.
- burning the trees would increase CO2 and
accounts for about 20% of CO2 added to
atmosphere by human activity.
B. Burning fossil fuels increases CO2 levels &
accounts for about 80% of CO2 added to
atmosphere by human activity.
Impact the Carbon cycle
C. Adding CO2 increases greenhouse effect (a
natural process)
1.CO2 & water vapor are some heat
absorbing gases.
2. These greenhouse gases let sunlight
through but then trap heat radiated from
Earth’s surface.
3. increasing them could possibly lead to
global warming (see Fig. 36-14)
Impact the Carbon cycle
D. Global warming is an increased average
temperature worldwide
E. Possible effects of global warming (even by
just a few degrees):
1. melting of glaciers & polar ice caps.
2. rise in sea level & flooding low-lying
coastal areas.
3. changes in weather patterns (precipitation).
4. boundaries between biomes might shift
and affect species.
Carbon dioxide
II. Human Activities Impact
Nitrogen Cycle
A. Some sewage treatment plants release
dissolved nitrogen compounds into streams &
rivers.
B. Fertilizers can run off into streams & ponds.
C. High levels of nitrogen (and phosphates) in
the water can cause eutrophication – rapid
growth of algae (algal bloom), which later die.
Bacteria decompose algae and use up so
much of the oxygen that the body of water
can no longer support other organisms.
Eutrophication
Impact Nitrogen Cycle
D. Burning fossil fuels releases nitrogen and
sulfur compounds into air. These compounds
combine with water in the air and form nitric
and sulfuric acid. Precipitation with these
acids is called acid rain.
1. Compounds in the atmosphere can travel
great distances. Compounds produced in the
Midwest of the U.S. create acid rain problems
in Eastern Canada
2. Clean Air Act has lessened problem in U.S.
by reducing levels of sulfur emissions.
III. Human Activities Impact
Water Cycle
A. Deforestation of tropical rainforests greatly
reduces amount of water vapor added to
atmosphere by transpiration.
- this can affect precipitation patterns which
affects ecosystems.
B. Drawing water from rivers and underground
aquifers faster than it’s replaced could cause
the aquifers to run dry.
IV. Other Effects of Pollution
A. Biological Magnification – the process by
which pollutants become more concentrated
in successive trophic levels of a food web
- example: PCBs from industrial wastes were
detected in tissues of organisms from the
Great Lakes. PCB levels
increased from 0.025 parts per million
(ppm) in phytoplankton to 124 ppm in herring
gull eggs.
- example: DDT caused shells of eagle eggs
to break easily. DDT use has been banned in
the U.S. and population of eagles has
recovered.
Effects of Pollution
B. The Ozone Shield, which absorbs harmful
ultraviolet radiation, has been thinning since the
1970’s. Chlorofluorocarbons (CFCs) released
from aerosol cans, refrigeration units, etc.,
destroy ozone (O3) molecules (see Fig. 36-18)
1. Increased exposure to UV radiation can cause:
- increased rates of skin cancer & cataracts.
- crop yields lessened & other producers harmed.
2. CFCs have been banned in many countries.
36.5 Conservation biology can
slow the loss of biodiversity
I. Why Diversity Matters
A. Many of the species in an ecosystem are
interconnected.
-Ex. if one species disappears, other species &
the health of the whole ecosystem may be
affected.
B. People value biodiversity (variety of life on Earth)
because:
1. organisms & ecosystems are sources of
beauty & inspiration.
2. organisms are sources of oxygen, food,
clothing, & shelter.
3. 25% of all medicines contain substances that
come from plants.
C. It’s important to conserve biodiversity for future
uses & needs.
II. Threats to Biodiversity
A. Throughout Earth’s history species have
become extinct – the last member of the
population died and the species no longer
exists on Earth.
B. Periods of mass extinction occurred as a
result of dramatic climate changes from
volcanic eruptions & asteroid impacts.
(ex.Dinosaur extinction at end of Cretaceous
period).
Threats to diversity
C. Currently a mass extinction is taking
place on Earth. It’s scale is uncertain
because the 1.5 million known species
are only a fraction of the total on Earth.
There are signs that species are
disappearing at a dramatic rate (page
806).
Threats to diversity
D. What threatens biodiversity?
1. Pollution
2. Habitat Destruction – as human population
grows, more land is cleared for agriculture,
roads, and communities.
3. Introduced (non-native) Species often prey
on native species & compete with them for
resources.
4. Overexploitation – the practice of harvesting
or hunting to such a degree that the small
number of remaining individuals may not be
able to sustain a population.
III. Conservation Biology
A. Focusing on Biodiversity Hot Spots, small
geographic areas with high concentrations
of species (see Fig. 36-23)
1. Many tend to be hot spots for extinction.
2. Global efforts are being taken to preserve some
hot spot areas.
B. Understanding an Organism’s Habitat – to
manage existing habitat or to create a new
one for a species
Conservation biology
C. Balancing Demands for Resources – efforts
to save species often conflict with the
economic & social needs of people.
D. Planning for a Sustainable Future
1. Nations establish zoned reserves – areas
of land that are relatively undisturbed by
humans, surrounded by buffer zones which
are minimally impacted by humans.
2. Sustainable development – developing
natural resources so that they can renew
themselves & be available for the future. (ex.
Selectively harvesting timber)