Chapter 36 – Ecosystems and Conservation Biology
Concept 36.1 Feeding relationships determine the path of energy and
chemicals in ecosystems.
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  chemical energy 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 (see below & Fig. 36-3).
Concept 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.
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.
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
I. Exception – organisms living in deep dark ocean 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. (see Figures 36-7 & 36-8)
Concept 36.3 Chemicals cycle in ecosystems.
How is it possible that some of the carbon atoms in an apple in your lunch
might once have been in a panda’s lung?
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 (see Fig. 36-10)
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.
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.
III. The Nitrogen Cycle (see Fig. 36-11)
A. Nitrogen is found in all living organisms in amino acids & other
essential molecules.
B. Almost 80% 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.
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.
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.
IV. The Water Cycle (see Fig. 36-12)
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.
Concept 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.
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)
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.
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.
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 produces 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 (see Fig. 36-17)
- 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.
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.
Concept 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).
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).
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 (the application of biology to counter the loss of
biodiversity)
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.
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)