13.1 Ecologists Study Relationships TEKS 2F, 3E, 10C
KEY CONCEPT
Ecology is the study of the relationships among
organisms and their environment.
13.1 Ecologists Study Relationships TEKS 2F, 3E, 10C
Ecologists study environments at different levels of
organization.
• Ecology is the study of the interactions among living
things, and between living things and their surroundings.
13.1 Ecologists Study Relationships TEKS 2F, 3E, 10C
• An organism is an individual living
thing, such as an alligator.
Organism
Organism
13.1 Ecologists Study Relationships TEKS 2F, 3E, 10C
• A population is a group of the same
species that lives in one area.
Population
Population
Organism
Organism
13.1 Ecologists Study Relationships TEKS 2F, 3E, 10C
• A community is a group of different
species that live together in one area.
Community
Community
Population
Population
Organism
Organism
13.1 Ecologists Study Relationships TEKS 2F, 3E, 10C
• An ecosystem includes all of the
organisms as well as the climate, soil,
water, rocks and other nonliving things
in a given area.
Ecosystem
Ecosystem
Community
Community
Population
Population
Organism
Organism
13.1 Ecologists Study Relationships TEKS 2F, 3E, 10C
• A biome is a major regional or global
community of organisms characterized
by the climate conditions and plant
communities that thrive there.
Biome
Ecosystem
Ecosystem
Community
Community
Population
Population
Organism
Organism
13.1 Ecologists Study Relationships TEKS 2F, 3E, 10C
Ecological research methods include observation,
experimentation, and modeling.
• Observation is the act of carefully watching something
over time.
• Observations of populations can be done by visual
surveys.
– Direct surveys for easy to spot
species employ binoculars or
scopes.
– Indirect surveys are used for
species that are difficult to
track and include looking for
other signs of their presence.
Ecological Methods
• Because this is not a controlled
experimental laboratory…
– Observing the ecosystem (footprints, scat,
counting organisms, signs of life)
– Experimental simulations of nature in a lab
– Computer models based on past data to
predict future trends
Section 2
13.2
Biotic and Abiotic Factors
TEKS 12F
KEY CONCEPT
Every ecosystem includes both living and nonliving
factors.
13.2
Biotic and Abiotic Factors
TEKS 12F
An ecosystem includes both biotic and abiotic factors.
• Biotic factors are living things.
– plants
– animals
– fungi
– bacteria
plants
13.2
Biotic and Abiotic Factors
• Abiotic factors are nonliving things.
– moisture
– temperature
– wind
– sunlight
– soil
TEKS 12F
sunlight
moisture
13.2
Biotic and Abiotic Factors
TEKS 12F
• A keystone species is a species that has an unusually large
effect on its ecosystem.
creation of
wetland
ecosystem
increased waterfowl
Population
keystone species
increased
fish
population
nesting
sites for
birds
Section 3
Energy Transfer
What is the main source of energy for
all Ecosystems?
From the sun, plants can make their
own food by photosynthesis and other
organisms can feed on them.
Some other organisms can make their
own food from inorganic compounds
(chemicals not containing carbon)
using chemosynthesis.
13.3
Energy in Ecosystems
TEKS 11C, 12C
Producers provide energy for other organisms in an
ecosystem.
• Producers get their energy from non-living resources.
• Producers are also called autotrophs because they make
their own food.
Autotrophs/Producersorganisms that can make their own
food from the sun or chemicals
• Plants capture sunlight and convert
CO2 and water into sugar (food) and
O₂ by photosynthesis.
–What was the formula again?
Types of Autotrophs
• Photoautotrophs- capture energy from
sunlight and convert it to carbohydrates
– Plants, algae, cyanobacteria
• Chemoautotrophs- capture energy from
heat and inorganic compounds and
convert it to carbohydrates
– Archaebacteria living in deep sea vents
Autotrophs/Producers–Some bacteria in extreme environments
capture energy from inorganic
compounds by chemosynthesis
Section 4
13.4 Food Chains And Food Webs
TEKS 11C, 12,C
KEY CONCEPT
Food chains and food webs model the flow of energy
in an ecosystem.
13.4 Food Chains And Food Webs
TEKS 11C, 12,C
A food chain is a model that shows a sequence of feeding
relationships.
• A food chain links species by their feeding relationships.
• A food chain follows the connection between one producer
and a single chain of consumers within an ecosystem.
GRAMA GRASS
DESERT COTTONTAIL
HARRIS’S HAWK
13.4 Food Chains And Food Webs
TEKS 11C, 12,C
• Specialists are consumers that primarily eat one specific
organism or a very small number of organisms.
• Generalists are consumers that have a varying diet.
Heterotrophs/Consumers
Organisms that
eat OR absorb
food to obtain
energy
Herbivores
Eat only plant life
ex. cows, deer, insects
Carnivores-
Feed on other
consumers
Ex: snakes, dogs,
anteaters
Omnivores
Eat both
producers and
other consumers
Ex: humans, bears,
crows
Detritivores and Scavengers:
Feed on dead
materials
Ex: mites,
earthworms, crabs
Decomposers
Break down organic
matter and return it
to the earth as
inorganic matter
Ex: bacteria,
fungi, fungus-like
protists
Detritivore vs.
Decomposer
• Break down dead
organic materials
• Break down dead
organic materials
• Only break down
some molecules
• Can break down
more complex
molecules
• Break down matter
more fully
13.4 Food Chains And Food Webs
TEKS 11C, 12,C
• Consumers are not all alike.
– Herbivores eat only plants.
– Carnivores eat only animals.
– Omnivores eat both plants and animals.
– Detritivores eat dead organic matter.
– Decomposers are detritivores that break down organic
matter into simpler compounds.
carnivore
decomposer
13.4 Food Chains And Food Webs
TEKS 11C, 12,C
• Trophic levels are the nourishment levels in a food chain.
– Primary consumers are herbivores that eat producers.
– Secondary consumers are carnivores that eat
herbivores.
– Tertiary consumers are carnivores that eat secondary
consumers.
– Omnivores, such as humans that eat both plants and
animals, may be listed at different trophic levels in
different food chains.
13.4 Food Chains And Food Webs
TEKS 11C, 12,C
A food web shows a complex network of feeding
relationships.
• An organism may have multiple feeding relationships in an
ecosystem.
• A food web emphasizes complicated feeding relationships
and energy flow in an ecosystem.
Put this one in your notes 
Producer
Primary
consumer
Secondary
consumer
Tertiary
consumer
Food Webs
Link together
several food
chains within
the same
ecosystem.
3
2
21
2
1
Purpose of food webs and chains:
• Show how energy flows in an
ecosystem
• Direction of the arrow is the
direction of the flow of energydo NOT mix this up!
Energy Flow
Energy flows in one direction
through an ecosystem:
Sun  Producers  Consumers  Decomposers
Along the way, some energy is
“lost” as heat (thermal energy)
What do you mean “lost as heat”?
• Energy cannot be created or destroyed,
only converted from one form to another
• Light energy is converted to chemical
energy stored in food (during
photosynthesis)
– Is all of the energy this plant makes available
to the organism that eats it?
What do you mean “lost as heat”?
• No! The plant USES some of it to grow, to
reproduce, to help make food, etc.
• Remember back to biochemistry, what
happens when we break chemical bonds?
– Energy is released as HEAT
– Hence through a food chain, much of the
energy is lost to the environment as heat.
Energy from the
sun enters the
first trophic level
ONLY 10% of the
total energy available
goes to the next level
But how much
energy?
Energy goes from
the Producers to the
first level consumers
It’s used for
life
processes or
lost to the
atmosphere
as heat
(thermal
energy)
What happens
to the other
90%?
Section 5
Biogeochemical
Cycles
Biogeochemical Cycles
While energy is
transferred in
one direction in
an ecosystem,
matter is cycled
through the
ecosystem in
the
biogeochemical
cycles
Biogeochemical Cycles
• Water cycle- how water moves
through the air, land, and organisms
–Evaporation- water vapor from
surface of bodies of water
–Transpiration- water vapor from plants
–Condensation- vapor water in clouds
Biogeochemical Cycles
• Water cycle- how water moves
through the air, land, and organisms
–Precipitation- clouds become too full
and rain, snow, etc. fall to the earth
–Runoff- water collects into bodies of
water
–Infiltration/Seepage- water from the
surface sinks into ground water storage
13.5 Cycling of Matter
TEKS 11C, 12E
Water cycles through the environment.
• The hydrologic, or water, cycle is the circular pathway of
water on Earth.
• Organisms all have bodies made mostly of water.
precipitation
condensation
transpiration
evaporation
lake
groundwater
surface
runoff
water storage
in ocean
13.5 Cycling of Matter
TEKS 11C, 12E
• Carbon is the building block of life.
– The carbon cycle moves carbon from the atmosphere,
through the food web, and back to the atmosphere.
– Carbon is emitted during the burning of fossil fuels.
– Some carbon is stored for long periods of time in areas
called carbon sinks.
carbon
dioxide
in air combustion
respiration
photosynthesis
respiration
decomposition
of organisms
fossil fuels
photosynthesis
carbon dioxide
dissolved in water
13.5 Cycling of Matter
TEKS 11C, 12E
• The nitrogen cycle mostly takes place underground.
– Some bacteria convert gaseous nitrogen into ammonia
through a process called nitrogen fixation.
– Some nitrogen-fixing bacteria live in
nodules on the
nitrogen in
atmosphere
roots of plants;
animals
others live
freely in
soil.
plant
nitrogen-fixing
bacteria in
decomposers
roots
ammonification
nitrogen-fixing
ammonium
bacteria in soil
nitrifying
bacteria
nitrates
nitrifying
bacteria
nitrites
denitrifying
bacteria
13.5 Cycling of Matter
TEKS 11C, 12E
– Ammonia released into the soil is transformed into
ammonium.
– Nitrifying bacteria change the ammonium into nitrate.
– Nitrogen moves through the food
web and returns nitrogen in
atmosphere
to the soil during
animals
decomposition.
plant
nitrogen-fixing
bacteria in
decomposers
roots
ammonification
nitrogen-fixing
ammonium
bacteria in soil
nitrifying
bacteria
nitrates
nitrifying
bacteria
nitrites
denitrifying
bacteria
Biogeochemical Cycles
Nitrogen Cycle:
-Nitrogen fixation- bacteria take nitrogen (N2)
from the atmosphere and change it into a
form that plants can take up from the soil
called ammonium (NH4).
-Nitrification- ammonium not taken up by
plants are converted to nitrates and nitrites
by bacteria which other plants can take up
Biogeochemical Cycles
Nitrogen Cycle:
-Consumers then eat and take in N in order
to make proteins.
-Dead organisms can return N to the soil or
to the atmosphere with the help of bacteria
-Denitrification- bacteria can turn the
ammonium back to atmospheric nitrogen
13.5 Cycling of Matter
TEKS 11C, 12E
• The phosphorus cycle takes place at and below ground
level.
– Phosphate is released by the weathering of rocks.
– Phosphorus moves through the food web and returns to
the soil during
decomposition.
rain
geologic uplifting
– Phosphorus leaches
into groundwater
weathering of
phosphate from rocks
from the soil and
runoff
plants
is locked in
sediments.
animalsphosphate
phosphate in solution
in soil
– Both mining and
leaching
agriculture add
sedimentation
phosphorus into
decomposers
forms new rocks
the environment.
Nutrient Limitations
• An ecosystem needs a particular amount
of each nutrient to thrive. A single nutrient
can limit its success.
• An excess of a particular nutrient can
cause over production of algae and plant
growth
Human Effects on Biogeochemical
Cycles
• Carbon- burning fossil fuels releases
previously isolated carbon back to the
atmosphere
• Nitrogen and Phosphorus- we add
fertilizers to assist crop growth and much
of it gets washed away into rivers, lakes
and oceans
• Eutrophication- overgrowth of
photosynthetic organisms in a body of
water due to an excess of nitrates and
phoshates from urban or agricultural runoff
In oceans
In lakes
• Eutrophication- overgrowth of
photosynthetic organisms in a body of
water due to an excess of nitrates and
phoshates from urban or agricultural runoff
In estuaries
Can choke the waters of
gas exchange
Section 6
Ecological Pyramids
The direction of energy flow through
the trophic levels can be shown
through food chains and food webs.
To show relative amounts of matter
and energy per trophic level, we can
use a pyramid
13.6 Pyramid Models
TEKS 12C
An energy pyramid shows the distribution of energy
among trophic levels.
• Energy pyramids compare energy used by producers
and other organisms on trophic levels.
• Between each tier of an energy
pyramid, up to 90 percent of the
energy is lost into the
atmosphere as heat.
• Only 10 percent of the energy at
each tier is transferred from one
trophic level to the next.
energy
lost
energy transferred
If 5600 kCal were
available at the
producer level,
how much would
be available at
each of the other
trophic levels?
5.6 kCal
56 kCal
560 kCal
5600 kCal
kCal
x10%
10%
kCal
5600
56056
kCal
kCal
xx10%
===
560
565.6
kCal
kCal
13.6 Pyramid Models
TEKS 12C
Other pyramid models illustrate an ecosystem’s biomass
and distribution of organisms.
• Biomass is a measure of the total dry mass of organisms in
a given area.
tertiary
consumers
75 g/m2
150g/m2
secondary
consumers
primary
consumers
producers
producers
675g/m2
2000g/m2
13.6 Pyramid Models
TEKS 12C
• A pyramid of numbers shows the numbers of individual
organisms at each trophic level in an ecosystem.
tertiary
consumers
5
secondary
consumers
5000
primary
consumers
500,000
producers
producers
5,000,000
• A vast number of producers are required to support even a
few top level consumers.