Unit 2
Ecology
Chapter 3 – The Biosphere
Introduction to Ecology
Ecology - the scientific study of interactions among
organisms and between organisms and their
physical environment.
Ecologist - a scientist who studies organisms as
they interact with other organisms within an
ecosystem
Levels of Organization
 Individual Organism
 Population—a group of individuals that belong to the
same species and live in the same area
 Community—an assemblage of different populations
that live together in a defined area
 Ecosystem—all the organisms that live in a place,
together with their physical environment
 Biome—a group of ecosystems that share similar
climates and typical organisms
 Biosphere—our entire planet, with all its organisms and
physical environments
Types of Ecosystems
Natural Ecosystems
 Self sustaining
 Precipitation
 Sunlight
 All resources to
support life
 Destroyed by
natural disasters
(fires)
Human-Made Ecosystems
 Not self sustaining
 Farms
 Cities
 Flower gardens
 Aquariums
 Zoo
 Huge inputs of
resources and energy
Relationships Within an Ecosystem
•An ecosystem is a group of organisms that live
together and interact with each other and their
environment.
•Organisms respond to their environments and can
change their environments, producing an everchanging biosphere.
Biotic
Factors
 Anything living in
an ecosystem!
 List three
example of
biotic
components in
an ecosystem
and how they
interact?
Abiotic
Factors
• Anything nonliving!
▫ List three
example of
abiotic
components in
an ecosystem
and why they
are important?
Biomes
• A large geographic region
determined by climate, soil
type and plant life.
oWhy is plant life so important
to an ecosystem?
Biomes
Arctic Tundra
Desert
Northern Coniferous
Forest or Taiga
Temperate Deciduous
Forest
Tropical Savanna
Temperate Grasslands
or Prairie
Tropical Rain Forest
Population Studies: factors that affect the
size of a population
1. Carrying
capacity:
The maximum
size of the
population
that an
ecosystem
can hold
2. Limiting factors:
Anything that
prevents the
population size
from increasing
Examples ?
Food Chains and Food
Webs
o How does energy flow through ecosystems?
o Energy flows through an ecosystem in a one-way stream, from primary
o producers to various consumers. Energy moves from the “eaten” to the “eater.”
Where it goes from there depends on who eats whom!
Food Chain
The arrows in a food chain show what
eats what. The arrow replaces the
phrase “is eaten by”.
The arrow must point toward the
“eater”.
Leaf

Grasshopper 
Frog
 Heron
Food Webs
• This is who eats who or what in the
ecosystem. Each organism has a “job title”
that describes their role. Anything that
affects one level will probably affect the
entire ecosystem!
Food Web
A food web shows the many possible food chains that exist in an ecosystem.
Food Webs “Job Titles”
• Producers- Plants. They are the
basis for life in the ecosystem.
• These organisms are also called
autotrophs.
Most Producers get Energy From the Sun
The best-known and most common primary producers harness
solar energy through the process of photosynthesis.
Photosynthesis captures light energy and uses it to power
chemical reactions that convert carbon dioxide and water into
oxygen and energy-rich carbohydrates. This process adds oxygen
to the atmosphere and removes carbon dioxide.
Most photosynthesis occurs in plants on land and algae in water
ecosystems.
Life Without Light
Deep-sea ecosystems depend on primary producers
that harness chemical energy from inorganic
molecules such as hydrogen sulfide.
The use of chemical energy to produce carbohydrates
is called chemosynthesis.
Food Webs “Job Titles”
• Consumers- these organism eat
other organisms. They can not
make their own food, therefore,
they must “order out”!
• Organisms that must acquire
energy from other organisms by
ingesting in some way are also
known as heterotrophs.
Food Webs “Job Titles”
•Consumers may be
herbivores (plant eaters),
carnivores (meat eaters) or
omnivores (both)
•Carnivores are usually
referred to as predators!
Food Webs “Job Titles”
▫ 1st or PRIMARY level consumers are
herbivores
▫ 2nd or SECONDARY level consumers
are carnivores or omnivores and eat
1st order consumers
▫ What are 3rd order (level) consumers?
Food Webs “Job Titles”
• Decomposers- These are the recycling
centers of the ecosystem. They breakdown dead organisms into nutrients in
the soil that plants can use as vitamins.
▫ Bacteria and Fungus
• Detritivores, feed on detritus particles
(what is left from the decomposers,)
often chewing or grinding them into
smaller pieces.
 giant earthworms
Food Webs “Job Titles”
Scavengers- Similar to
decomposers because
they eat already dead
organisms and return
nutrients to the soil.
Animals, birds, insects
Trophic Levels and
Ecological Pyramids
o Each step in a food chain or food web is called a trophic level.
• Primary producers always make up the first trophic level.
• Various consumers occupy every other level. Some examples
are shown.
o Ecological pyramids show the relative amount of energy or matter
contained within each trophic level in a given food chain or food
web.
Advantages and Disadvantages of
the Pyramids
• Pyramids of numbers and biomass can sometimes
be inverted due to certain situations within
ecosystems
• These inverted pyramids then lose their ability to
accurately represent the passage of energy from
one trophic level to the next
Pyramid
of
Numbers
• This
represents
the number
of organisms
that occupy
each trophic
level
http://openlearn.open.ac.uk
Pyramids of Energy
o Pyramids of energy show the relative amount of energy
available at each trophic level.
o On average, about 10 percent of the energy available within
one trophic level is transferred to the next trophic level.
o The more levels that exist between a producer and a
consumer, the smaller the percentage of the original energy
from producers that is available to that consumer.
Pyramid of Biomass
o The total amount of living tissue within a given trophic
level is called its biomass.
o A pyramid of biomass illustrates the relative amount
of living organic matter at each trophic level.
Recycling in the Biosphere
o Unlike the one-way flow of energy, matter is recycled
within and between ecosystems.
o Elements pass from one organism to another and
among parts of the biosphere through closed loops
called biogeochemical cycles, which are powered by
the flow of energy.
• Biogeochemical cycles of matter involve biological
processes, geological processes, and chemical
processes.
Recycling in the Biosphere
o As matter moves through these cycles, it is
never created or destroyed—just changed.
• Biogeochemical cycles of matter pass the
same atoms and molecules around again
and again.
Water Cycle
• Also called the Hydrologic
Cycle
• Movement and storage of
water on the planet
o Total amount of water
doesn’t change – it is
transported around the
earth
o Energy to run the cycle
comes from the sun
• Water re-enters that atmosphere by two processes
o Evaporation changes surface water
(lakes, rivers, oceans) to water vapor
• Water vapor (gaseous state) returns to
the atmosphere
o Transpiration is the loss of water vapor
from the leaves of plants
• Stomata are openings in leaves which
allow the water vapor out of the plant
• Condensation
o As the water vapor rises in the atmosphere, it
looses energy (cools down)
o Water droplets are formed from the water vapor
• Precipitation
o When the water droplets get too heavy it falls
from the sky
o Weather conditions determine the type of
precipitation – rain, snow, sleet
• Some precipitation re-evaporates before it reaches
the ground
• Most precipitation falls into existing bodies of water
o 70% of the earth’s surface is water
• The rest falls on land
o Absorbed into the soil or flows over the surface as
Runoff (back to the oceans/lakes)
o Infiltration is the process of water entering the
ground
The cycle begins again:
o Evaporation and transpiration
o Condensation
o Precipitation
o Runoff and Infiltration
 The amount of precipitation is an important factor in
the type of ecosystem and the population of
organisms it can support
Nutrient Cycles
o The chemical substances that an organism needs to
sustain life are called nutrients.
o Every organism needs nutrients to build tissues and
carry out life functions.
o Nutrients pass through organisms and the environment
through biogeochemical cycles.
The Carbon – Oxygen
Cycle
o Carbon is a major component of all organic
compounds, including carbohydrates, lipids, proteins,
and nucleic acids.
The Carbon – Oxygen
Cycle
• Plants take in carbon dioxide during
photosynthesis and use the carbon to build
carbohydrates.
• Carbohydrates then pass through food webs to
consumers.
• Organisms release carbon in the form of carbon
dioxide gas by respiration.
The Nitrogen Cycle
o All organisms require nitrogen to make amino acids,
which are used to build proteins and nucleic acids,
which combine to form DNA and RNA.
The Nitrogen Cycle
o Nitrogen-containing substances such as ammonia
(NH3), nitrate ions (NO3), and nitrite ions (NO2) are
found in soil, in the wastes produced by many
organisms, and in dead and decaying organic matter.
The Nitrogen Cycle
o Nitrogen gas (N2) makes up 78 percent of Earth’s
atmosphere.
• Although nitrogen gas is the most abundant form
of nitrogen on Earth, only certain types of bacteria
that live in the soil and on the roots of legumes can
use this form directly.
o The bacteria convert nitrogen gas into ammonia, in a
process known as nitrogen fixation.
The Nitrogen Cycle
o Other soil bacteria convert fixed nitrogen into nitrates
and nitrites that primary producers can use to make
proteins and nucleic acids.
o Consumers eat the producers and reuse nitrogen to
make their own nitrogen-containing compounds
The Nitrogen Cycle
o Consumers eat the producers and reuse nitrogen to
make their own nitrogen-containing compounds.
o Decomposers release nitrogen from waste and dead
organisms as ammonia, nitrates, and nitrites that
producers may take up again.
The Nitrogen Cycle
o Other soil bacteria obtain energy by converting
nitrates into nitrogen gas, which is released into the
atmosphere in a process called denitrification.
o A small amount of nitrogen gas is converted to usable
forms by lightning in a process called atmospheric
nitrogen fixation.
o Humans add nitrogen to the biosphere through the
manufacture and use of fertilizers. Excess fertilizer is
often carried into surface water or groundwater by
precipitation.
The Phosphorus Cycle
o Phosphorus forms a part of vital molecules such as
DNA and RNA.
o Although phosphorus is of great biological
importance, it is not abundant in the biosphere.
o Phosphorus in the form of inorganic phosphate
remains mostly on land, in the form of phosphate rock
and soil minerals, and in the ocean, as dissolved
phosphate and phosphate sediments.
The Phosphorus Cycle
o As rocks and sediments wear down, phosphate is
released
o Plants bind phosphate into organic compounds when
they absorb it from soil or water.
o Organic phosphate moves through the food web, from
producers to consumers, and to the rest of the
ecosystem.
Nutrient Limitation
o Ecologists are often interested in an ecosystem’s
primary productivity—the rate at which primary
producers create organic material.
o A nutrient whose supply limits productivity is called the
limiting nutrient.
▫ All nutrient cycles work
together like the gears shown.
▫ If any nutrient is in short
supply—if any wheel “sticks”—
the whole system slows down
or stops altogether.
Nutrient Limitation in Aquatic
Ecosystems
o Sometimes an aquatic ecosystem receives a large
input of a limiting nutrient—for example, runoff from
heavily fertilized fields.
o The result of this runoff can be an algal bloom—a
dramatic increase in the amount of algae and other
primary producers due to the increase in nutrients.