13.1 Ecologists Study Relationships
KEY CONCEPT
Ecology is the study of the relationships among
organisms and their environment.
13.1 Ecologists Study Relationships
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
• An organism is an individual living
thing, such as an alligator.
Organism
Organism
13.1 Ecologists Study Relationships
• A population is a group of the same
species that lives in one area.
Population
Population
Organism
Organism
13.1 Ecologists Study Relationships
• 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
• 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
• 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
Bell Ringer
• List the ecological levels of organization, beginning with
the smallest.
• What was the name of the “scientific equipment” that we
modeled in class yesterday?
• What are some reasons why we might need to estimate
the number of organisms living in an area?
13.1 Ecologists Study Relationships
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.
13.1 Ecologists Study Relationships
• Experiments are performed in the lab or in the field.
– Lab experiments give researchers more control.
– Lab experiments are not reflective of the complex
interactions in nature.
– Field experiments give a
more accurate picture of
natural interactions.
– Field experiments may
not help determine
actual cause and effect.
13.1 Ecologists Study Relationships
• Computer and mathematical models can be used to
describe and model nature.
• Modeling allows scientists to learn about organisms or
ecosystems in ways that would not be possible in a
natural or lab setting.
Ecologists use data transmitted
by GPS receivers worn by
elephants to develop computer
models of the animal’s
movements.
13.1 Ecologists Study Relationships
Calculate…
Below is a field full of dandelions. Rather than counting every
dandelion, which would be extremely time-consuming and
almost impossible, you have been asked to complete an analysis
based on random sampling. Based on the information given
below, calculate approximately how many dandelions you would
expect to find in this field. You must show your work.
11
21
15
19
6
8
13.1 Ecologists Study Relationships
• Estimate the total number of daisies in a field using
random sampling…
16
32
17
14
21
19
26
13.1 Ecologists Study Relationships
KEY CONCEPT
Every ecosystem includes both living and nonliving
factors.
13.1 Ecologists Study Relationships
An ecosystem includes both biotic and abiotic factors.
• Biotic factors are living things.
– plants
– animals
– fungi
– bacteria
plants
13.1 Ecologists Study Relationships
• Abiotic factors are nonliving things.
– moisture
– temperature
– wind
– sunlight
– soil
sunlight
moisture
13.1 Ecologists Study Relationships
Changing one factor in an ecosystem can affect many
other factors.
• Biodiversity is the assortment, or variety, of living things in
an ecosystem.
• Rain forests have more biodiversity than other locations in
the world, but are threatened by human activities.
13.1 Ecologists Study Relationships
• A keystone species is a species that has an unusually large
effect on its ecosystem.
keystone
13.1 Ecologists Study Relationships
13.1 Ecologists Study Relationships
• Keystone species form and maintain a complex web of life.
creation of
wetland
ecosystem
increased waterfowl
Population
keystone species
increased
fish
population
nesting
sites for
birds
13.1 Ecologists Study Relationships
KEY CONCEPT
Life in an ecosystem requires a source of energy.
13.1 Ecologists Study Relationships
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.
13.1 Ecologists Study Relationships
Producers provide energy for other organisms in an
ecosystem.
• Consumers are organisms that get their energy by eating
other living or once-living resources.
• Consumers are also called heterotrophs because they feed off of
different things.
13.1 Ecologists Study Relationships
Almost all producers obtain energy from sunlight.
• Photosynthesis in most producers uses sunlight as an
energy source.
• Chemosynthesis in prokaryote producers uses chemicals
as an energy source.
carbon dioxide +
water +
hydrogen sulfide +
oxygen
13.1 Ecologists Study Relationships
KEY CONCEPT
Food chains and food webs model the flow of energy
in an ecosystem.
13.1 Ecologists Study Relationships
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
13.1 Ecologists Study Relationships
• 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
13.1 Ecologists Study Relationships
• Specialists are consumers that primarily eat one specific
organism or a very small number of organisms.
• Generalists are consumers that have a varying diet.
13.1 Ecologists Study Relationships
• 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.
13.1 Ecologists Study Relationships
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.
13.1 Ecologists Study Relationships
13.1 Ecologists Study Relationships
KEY CONCEPT
Pyramids model the distribution of energy and matter
in an ecosystem.
13.1 Ecologists Study Relationships
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
13.1 Ecologists Study Relationships
Calculate Energy Transferred
• A total of 17,500 kcal of energy is available in the first
trophic level. Only 10.3% of that energy is transferred to
the second trophic level. How much energy will be
available to the second trophic level?
13.1 Ecologists Study Relationships
• If 12,000 kcal of energy is available to the producers, and
9.6 % of that is transferred to the primary consumers,
then 10.2% of that available energy is transferred to the
secondary consumers, how much total energy will the
secondary consumers receive?
13.1 Ecologists Study Relationships
• In a desert ecosystem, a cactus receives 13,600 J of
energy from the sunlight. Of that energy, 10.6% is
transferred to the insects. The insects are then eaten by
lizards, which receive 9.9% of the available energy.
Finally, 9.4% of the energy is transferred to the hawk
when they eat the lizards. How much energy is available
at the tertiary consumer level? Show your work. Place a
box around your final answer—units included!
13.1 Ecologists Study Relationships
• The unit of measure for the energy transferred between
trophic levels is a kilocalorie (kcal)
13.1 Ecologists Study Relationships
13.1 Ecologists Study Relationships
13.1 Ecologists Study Relationships
Biomass Pyramid
• Biomass is a measure
of the total dry mass of
organisms in a given
area.
• Provides a picture of
the mass of producers
needed to support
primary consumers, the
mass of primary
consumers required to
support secondary
consumers, etc.
• Illustrates the important
role producers play in
maintaining a stable
ecosystem
tertiary
consumers
75 g/m2
150g/m2
secondary
consumers
primary
consumers
producers
producers
675g/m2
2000g/m2
13.1 Ecologists Study Relationships
Pyramid of Numbers
• 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.
13.1 Ecologists Study Relationships
13.1 Ecologists Study Relationships
Pyramid of Numbers
• What would a pyramid of numbers look like if our primary
producer was a tree? Think for a moment…
13.1 Ecologists Study Relationships
Review
• How does an energy pyramid help to describe energy flow in
a food web?
• What is the difference between a biomass pyramid and a
pyramid of numbers?
• If each level in a food chain typically loses 90% of the energy
it takes in, and the producer level uses 1000 kcal of energy,
how much of that energy is left after the third trophic level?
13.1 Ecologists Study Relationships
KEY CONCEPT
Matter cycles in and out of an ecosystem.
13.1 Ecologists Study Relationships
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
13.1 Ecologists Study Relationships
Elements essential for life also cycle through
ecosystems.
• A biogeochemical cycle is the movement of a particular
chemical through the biological and geological parts of an
ecosystem.
• The main processes involved in the oxygen cycle are
photosynthesis and respiration.
13.1 Ecologists Study Relationships
• Oxygen cycles indirectly through an ecosystem by the
cycling of other nutrients.
oxygen
photosynthesis
respiration
carbon
dioxide
13.1 Ecologists Study Relationships
• Carbon is the building block of life.
– The carbon cycle moves carbon from the atmosphere,
through the food web, and returns to the atmosphere.
– Carbon is emitted by 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
13.1 Ecologists Study Relationships
Nitrogen Cycle
• 78% of Earth’s atmosphere is made of nitrogen gas
• 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
roots of plants; others live freely in the soil.
13.1 Ecologists Study Relationships
– 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
13.1 Ecologists Study Relationships
• The phosphorus cycle takes place at and below ground level.
– Unlike the other cycles, the phosphorus cycle does not include an
atmospheric portion
– Phosphate is released by the weathering of rocks.
– Phosphorus moves through the food web and returns to the soil during
decomposition.
– Phosphorus leaches into
groundwater from the soil and is
rain
geologic uplifting
locked in sediments.
– Both mining and
weathering of
phosphate from rocks
agriculture add
runoff
plants
phosphorus into
the environment.
animals
phosphate
phosphate in solution
in soil
leaching
decomposers
sedimentation
forms new rocks