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Chapter 18
Intro to Ecology
18.1 – INTRO TO ECOLOGY
What is ecology?
• the study of interactions between
organisms and the living and nonliving
components of their environment
What does ecology involve?
• Collecting info about organisms and
their environments
• Observing/measuring interactions
between organisms
• Looking for patterns among organisms
and their environments and explaining
Interdependence
• A key theme in biology
• Refers to interconnectedness of
organisms with each other and with
the nonliving parts of their
environment
• Any change in the environment can
affect the network of interactions and
organisms seemingly far removed from
the change
Levels of
Organization
From largest to smallest:
•Biosphere
•(Biomes)
•Ecosystem
•Community
•Population
•Organism
•These levels of
organization are
considered external as
opposed to the internal
levels that we learned
earlier.
Recall internal levels of
organization beginning with atoms:
atoms
biological molecules
cell organelles
cells **Internal organization for unicellular organisms stops here
tissues
Remember that these internal levels
organs
exist only in multicellular organisms!
organ systems
organism
Ecological levels of organization
defined:
• organism – individual living thing
• population – group of organisms of the
same species living in the same area
• community – all of the interacting organisms
living in an area
• ecosystem – living (biotic) and nonliving
(abiotic) things found in a particular area
• biosphere – the thin volume of Earth
(extending below the surface and into the
atmosphere) that supports life
18.2 – ECOLOGY OF ORGANISMS
Ecosystem Components:
Biotic
Abiotic
Definition:
Living parts
Nonliving (physical
and chemical) parts
Examples:
All the organisms:
plants, animals,
bacteria, fungi,
protists
Temperature, pH,
oxygen, nitrogen,
humidity, salinity,
sunlight,
precipitation, etc.
Ecosystem Components:
Aquatic vs. Terrestrial
Biotic
Abiotic
Aquatic ecosystem
Algae and other
protists, plants,
animals, bacteria
Water temp., depth,
turbidity, salinity, still
vs. current or waves,
pH, sunlight, oxygen,
etc.
Terrestrial ecosystem
Protists, fungi, plants,
animals, bacteria
Temp., sunlight,
humidity, precipitation,
soil minerals, etc.
18.3 – ENERGY TRANSFER
Why do organisms need energy?
• To carry out life functions like:
– growth
– repair
– maintenance
– movement
– reproduction
• Energy flows in an ecosystem.
• The amount of energy that an
ecosystem receives and the amount
that’s transferred from organism to
organism affects the ecosystem’s
structure.
Within an ecosystem there are
producers and consumers
Producers
Consumers
Definition
Capture energy and
make organic molecules
Eat other organisms or organic
wastes for energy
Groups
Photosynthetic: capture
sunlight to make org.
molecules
Herbivores: eat producers
Chemosynthetic: use
inorganic molecules to
make org. molecules
Carnivores: eat other consumers
Omnivores: eat producers and
consumers
Detritivores: feed on wastes like
dead organisms, fallen leaves,
animal waste, etc.
Decomposers: detritivores that
cause decay by breaking down
complex molecules into simpler
ones
Producers
Exp.
Consumers
PS: Plants, some
H: Antelope
protists, some bacteria
C: Lions, cobras,
praying mantises
CS: Some bacteria
O: Grizzly bear
Det.: Vulture
Dec: Bacteria and
fungi
Biomass
• Organic materials produced in an
ecosystem
• Producers add to the biomass by
making organic molecules!
Decomposers
• “nature’s recyclers”
• cause decay; make nutrients trapped
in waste available again to autotrophs
Energy Flow
• Trophic level – organism’s position in a
sequence of energy transfers
– 1st level = producers
– 2nd level = herbivores
– 3rd level = primary consumers
– 4th level = secondary consumers
– 5th level = tertiary consumers
Food chains vs. food webs
• Food chains – show a single pathway
of energy flow
• Single food chains are rare in nature
• Food webs – interrelated food chains
in an ecosystem
Energy transfer
How much energy is available for each
trophic level?
• On average, 10 percent of the total energy
consumed in one trophic level is incorporated into
the organisms in the next
• Why only 10%?! Organisms:
– escape being eaten
– die and become food for decomposers
– have energy stored in places that can’t be used
(like antlers)
– need/use energy themselves
– some energy is also lost in metabolism (heat) –
remember that cell respiration is only 39%
efficient!
Eat 3° consumers
Eat 2° consumers
Eat 1° consumers
Eat producers
Produce chemical
energy from
sunlight
Limitations of trophic levels
• Ecosystems rarely have more than a
few trophic levels
– Since only 10 percent is available to next
level, there’s not enough energy in the
top level to support more levels
– Organisms at lowest level usually much
more abundant; more diversity at
lowest level; high levels contain less
energy and can support fewer individuals
This energy pyramid diagram
represents energy flow through four
trophic levels.
At the lowest level,
there are a lot of
producers, so the block
is very wide.
Only 10% of the energy is
available to the next level, so
there are less organisms that
can exist at the level; there is
less diversity. The block is
smaller.
This continues up the
pyramid resulting in smaller
and smaller blocks – fewer
organisms being supported.
Pyramids may be shaped a
little differently depending
on the ecosystem, but
always follow this basic
pattern
18.4 – ECOSYSTEM RECYCLING
3 Biogeochemical Cycles:
• Water cycle
• Carbon cycle (carbon/oxygen cycle)
• Nitrogen cycle
• These cycles are pathways of these
materials from the environment, into
living things, and back into the
environment.
Water cycle includes:
• Evaporation - water enters the atmosphere from
oceans, lakes, streams, etc.
• Transpiration - water enters atmosphere by
evaporating out of plant leaves when stomata open
• Condensation – vapor to liquid
• Precipitation – falling forms of water
• Runoff – from land into water
• Percolation – water filters down through soil/rocks
• Groundwater – water beneath the surface in rock
formations or spaces
Carbon cycle
• Cellular respiration – releases carbon
into atmosphere (CO2)
• Photosynthesis * - uses carbon
• Decomposition – releases carbon
– Fossil fuels – formed from the remains of
dead organisms
• Combustion – burning of fossil fuels
and other organic materials; releases
carbon
Nitrogen cycle
• All organisms need nitrogen to make
– Proteins (amine group in amino acids has
N)
– Nucleic acids (nitrogenous bases A, T, C,
G, and U have nitrogen!)
• 78% of the atmosphere is nitrogen gas
(N2) BUT plants can’t use it in that
form...
• It must be converted into nitrates
(NO3)
• The process of converting nitrogen gas
into nitrates is nitrogen fixation
• Nitrogen-fixing bacteria convert
nitrogen gas into a usable form
– Live in soil
– Live in nodules on roots of some plants
like beans, peas, clover, and alfalfa
Parts of the nitrogen cycle
• Nitrogen fixation – converting nitrogen
gas into nitrates
• Ammonification – formation of
ammonia (NH3) and ammonium (NH4)
in the soil from decomposition of dead
organisms
• Nitrification – performed by soil
bacteria; uptake of ammonium and its
oxidation into nitrites (NO2-) and
nitrates (NO3-)
– Erosion of nitrate rich rocks also releases
nitrates into the ecosystem
– Plants use nitrates! Yay! They can
absorb them from the soil. Animals
cannot. Boo! So how do animals get
nitrogen?
• Assimilation – uptake of nitrates in soil
by plants
• Denitrification – performed by
anaerobic bacteria; breakdown of
nitrates that releases nitrogen gas
back into the atmosphere
Summary of Nitrogen cycle
1. Nitrogen fixing from air to soil.
2. Nitrogen in soil gets assimilated
into living things.
3. Living things excrete nitrogen and
die, nitrogen goes back into soil.
4. Bacteria convert soil Nitrogen back
into atmosphere.