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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
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.
13.2 Biotic and Abiotic Factors
KEY CONCEPT
Every ecosystem includes both living and nonliving
factors.
13.2 Biotic and Abiotic Factors
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
sunlight
moisture
13.2 Biotic and Abiotic Factors
Changing one factor in an ecosystem can affect many
other factors.
• Biodiversity is the assortment, or variety, of living things in
an ecosystem.
• Example: Rain forests have more biodiversity than other
locations in the world, but are threatened by human
activities.
13.2 Biotic and Abiotic Factors
• A keystone species is a species that has an unusually
large effect on its ecosystem.
keystone
13.2 Biotic and Abiotic Factors
• Keystone species form and maintain a complex web of life.
– Example: Beaver
creation of
wetland
ecosystem
increased waterfowl
Population
keystone species
increased
fish
population
nesting
sites for
birds
13.3 Energy in Ecosystems
KEY CONCEPT
Life in an ecosystem requires a source of energy.
13.3 Energy in Ecosystems
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.
13.3 Energy in Ecosystems
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.
13.3 Energy in Ecosystems
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
sugar + sulfuric acid
13.4 Food Chains And Food Webs
KEY CONCEPT
Food chains and food webs model the flow of energy
in an ecosystem.
13.4 Food Chains And Food Webs
A food chain is a model that shows a linear 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
• 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
13.4 Food Chains And Food Webs
• Specialists are consumers that primarily eat one specific
organism or a very small number of organisms.
• Generalists are consumers that have a varying diet.
13.4 Food Chains And Food Webs
• 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 depending on the situation
13.4 Food Chains And Food Webs
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.
13.4 Food Chains And Food Webs
13.5 Cycling of Matter
KEY CONCEPT
Matter cycles in and out of an ecosystem.
13.5 Cycling of Matter
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
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.
13.5 Cycling of Matter
• Oxygen cycles indirectly through an ecosystem by the
cycling of other nutrients.
oxygen
photosynthesis
respiration
carbon
dioxide
13.5 Cycling of Matter
• 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
13.5 Cycling of Matter
• 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
the 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
– 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
13.5 Cycling of Matter
• 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.
13.6 Pyramid Models
KEY CONCEPT
Pyramids model the distribution of energy and matter
in an ecosystem.
13.6 Pyramid Models
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.
Called the “10% Rule”
energy
lost
energy transferred
13.6 Pyramid Models
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
• 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.