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Ecology Review
An ecosystem contains:
• Biotic (living) components and
• Abiotic (nonliving) components.
The biotic components of ecosystems
are the populations of organisms.
The abiotic components include
inorganic nutrients, water,
temperature, and wind.
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Levels of ecological organization:
•Organism – a living thing capable of carrying on
the processes of life
•Population – a group of organisms of the same
species that live in a specific area
•Community – a group of several species that live
together and interact in a particular area
•Ecosystem – A community of organisms and
their abiotic components
•Biome – A large region characterized by a
specific climate and certain types of plant &
animal communities
•Biosphere – all of the ecosystems of the earth
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Largest  smallest
• Biosphere
• Biome
• Ecosystem
• Community
• Population
• Organism
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Biotic Components of an Ecosystem
Autotrophs are producers that produce
food for themselves and for
consumers.
Most are photosynthetic organisms but
some chemosynthetic bacteria are
autotrophs.
Heterotrophs are consumers that take
in preformed food.
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Biotic components
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Consumers may be:
Herbivores – animals that eat plants,
Carnivores – animals that eat other animals,
Omnivores, such as humans, that eat plants
and animals, or
Decomposers, bacteria and fungi, that
break down dead organic waste.
Detritus is partially decomposed organic
matter in the soil and water; beetles,
earthworms, and termites are detritus
feeders.
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Consumers
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Primary consumer – an organism that
gets its energy from plants (producers)
Secondary consumer – a consumer that
gets its energy from primary consumers
Tertiary consumer – carnivores that eat
other carnivores; a top-level consumer,
which is usually the top predator in the
food chain
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Energy Flow and Chemical Cycling
Every ecosystem is characterized by
two phenomena:
1) Energy flows in one direction from
the sun to producers through
several levels of consumers, and
2) Chemicals cycle when inorganic
nutrients pass from producers
through consumers and returned to
the atmosphere or soil.
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Only a small portion of energy and
nutrients made by autotrophs is
passed on to heterotrophs, and only a
small amount is passed to each
succeeding consumer; much energy
is used at each level for cellular
respiration and much is lost as heat.
Ecosystems are dependent on a
continual supply of solar energy.
The laws of thermodynamics support
the concept that energy flows through
an ecosystem.
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Energy balances
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Nature of an ecosystem
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Food chains vs. food webs
A food chain is diagram that link organisms
together by who eats whom; starts with plant
life and ends with an animal. Most food chains
have no more than 4 or 5 links
Ex: tree  giraffe  lion
Most animals are part of more than 1 food chain
& eat more than 1 kind of food in order to meet
their food and energy requirements. These
interconnected food chains form a food web.
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Food chain
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Forest food webs
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Generally, the upper portion of a food
web is a grazing food web, based on
living plants, and the lower portion is
a detrital food web, based on detritus
and the organisms of decay.
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Trophic Levels
A trophic level is all the organisms that
feed at a particular link in a food chain.
A grazing food chain:
Leaves → caterpillars → tree birds
→ hawks
A detrital food chain:
Dead organic matter → soil
microbes → worms
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Ecological Pyramids
The shortness of food chains can be
attributed to the loss of energy
between trophic levels.
Generally, only about 10% of the
energy in one trophic level is
available to the next trophic level.
This relationship explains why so few
carnivores can be supported in a food
web.
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The flow of energy with large losses
between successive trophic levels can
be depicted as an ecological pyramid
that shows trophic levels stacked one
on the other like building blocks.
Usually a pyramid shows that biomass
and energy content decrease from one
trophic level to the next, but an
inverted pyramid occurs where the
algae grow rapidly and are consumed
by long-lived aquatic animals.
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Ecological pyramid
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Biotic interactions:
•Predation - an interaction between two
organisms in which one organism kills and feeds
on the other organism
•Parasitism – a relationship between two species
in which one organism benefits while the other is
harmed
•Symbiosis – a relationship in which two species
live in close association with one another – ex:
mutualism and commensalism
• Mutualism – both species benefit
• Commensalism – one species benefits while
the other is neither harmed nor hurt
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Examples of biotic interactions:
•Predation – lion feeds on zebra
•Parasitism – tapeworms in the intestines
of another organism
•Mutualism – small fish cleans big fish
•Commensalism – orchids attach
themselves to the trunks of trees to get
more sunlight in the forest
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• Limiting factors – factors that can affect the
size of a population
• Abiotic limiting factors – weather, climate,
amount of water available
• Biotic limiting factors – amount of food
available, diseases and parasites,
number of predators, human activities
(such as habitat disruption, introducing
diseases, introducing non-native species,
pollution, fires)
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Biochemical cycles
•
•
•
•
Water Cycle
Carbon Cycle
Nitrogen Cycle
Phosphorous Cycle
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The Water Cycle
In the water, or hydrologic cycle, the sun’s
rays cause fresh water to evaporate from
the oceans, leaving the salts behind.
Vaporized fresh water rises into the
atmosphere, cools, and falls as rain over
oceans and land.
Precipitation, as rain and snow, over land
results in bodies of fresh water plus
groundwater, including aquifers.
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Water is held in lakes, ponds, streams, and
groundwater.
Evaporation from terrestrial ecosystems
includes transpiration from plants.
Eventually all water returns to the oceans.
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The water cycle
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The Carbon Cycle
In the carbon cycle, a gaseous cycle,
organisms exchange carbon dioxide with the
atmosphere.
Shells in ocean sediments, organic
compounds in living and dead organisms,
and fossil fuels are all reservoirs for carbon.
Fossil fuels were formed during the
Carboniferous period, 286 to 360 million
years ago.
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The carbon cycle
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The Nitrogen Cycle
Nitrogen makes up 78% of the atmosphere
but plants are unable to make use of this
nitrogen gas and need a supply of
ammonium or nitrate.
The nitrogen cycle, a gaseous cycle, is
dependent upon a number of bacteria.
During nitrogen fixation, nitrogen-fixing
bacteria living in nodules on the roots of
legumes convert atmospheric nitrogen to
nitrogen-containing organic compounds
available to a host plant.
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Cyanobacteria in aquatic ecosystems and
free-living bacteria in the soil also fix
nitrogen gas.
Bacteria in soil carry out nitrification when they
convert ammonium to nitrate in a two-step
process: first, nitrite-producing bacteria
convert ammonium to nitrite and then
nitrate-producing bacteria convert nitrite to
nitrate.
During denitrification, denitrifying bacteria in
soil convert nitrate back to nitrogen gas but
this does not quite balance nitrogen fixation.
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The nitrogen cycle
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The Phosphorus Cycle
The phosphorus cycle is a sedimentary cycle.
Only limited quantities are made available to
plants by the weathering of sedimentary
rocks; phosphorus is a limiting inorganic
nutrient.
The biotic community recycles phosphorus
back to the producers, temporarily
incorporating it into ATP, nucleotides, teeth,
bone and shells, and then returning it to the
ecosystem via decomposition.
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The phosphorus cycle
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