Chapter 3 : The Biosphere and Ecology
I. What is Ecology?
A. Interactions and Interdependence
Ecology – the scientific study of
interactions among organisms and
between organisms and their
environment/surroundings.
-The word ecology was coined by
German biologist Ernst Haeckel and
comes from Greek oikos (house). He
saw the living world as a household
with an economy in which each
organism plays a role.
The Biosphere
-Nature has many levels, the
largest of which is the Biosphere –
all of the combined portions of the
planet in which all of life exists,
including land, water, and air, or
atmosphere.
It extends from about 8 kilometers
above Earth’s surface to as far as
11 kilometers below the surface of
the ocean.
-Interactions within the everchanging biosphere produce a
web of interdependence between
organisms and their environments.
B. Levels of Organization
*The biosphere (highest level of
organization) can be broken down
into 5 basic levels of organization :
1. Individuals – single organisms
that can be grouped into species
– a group of organisms so
similar to one another that they
can breed and produce fertile
offspring.
2. Populations – groups of
individuals that belong to the
same species and live in the
same area.
B. Levels of Organization
3. Communities –
assemblages of different
populations that live
together in a defined area.
4. Ecosystems – a collection
of all the organisms that
live in a particular place,
together with their
nonliving, or physical,
environment.
5. Biomes – a group of
ecosystems that have the
same climate and similar
dominant communities.
C. Ecological Methods
*Scientists conduct modern ecological research using
three basic approaches :
1. Observing – the first step in asking ecological
questions or designing experiments and models
(gathering information).
2. Experimenting – testing hypotheses, ex : setting up an
artificial environment.
3. Modeling – creating models to gain insight into
complex phenomena that occur over long periods of
time and large spatial scales, ex : global warming.
Usually consist of mathematical formulas based on
data collected through observation and
experimentation.
II. Energy Flow
*The flow of energy through an
ecosystem is one of the
most important factors that
determines the system’s
capacity to sustain life. Without a
constant input of energy,
living systems can’t function.
A. Producers
-Sunlight is the main energy
source for life on Earth.
Although only a small amount of
the sun’s energy (less than 1%) is
used by living things, it is enough
to fuel existence on Earth.
Producers Con’t.
-Not all organisms obtain
energy from the sun; some
rely on the energy stored in
inorganic chemical compounds
for fuel, ex : hot springs and
undersea vents.
Autotrophs – organisms that can
capture energy from sunlight or
chemicals and use that energy to
produce food, ex : plants, algae, &
bacteria.
Autotrophs
-Autotrophs use energy from the
environment to take simple
inorganic compounds and turn
them into complex organic
molecules. These molecules
combine and recombine to
produce living tissue.
-Autotrophs are also known as
producers – organisms that make
their own food from sunlight or
chemicals and play a key role in
the flow or energy through the
biosphere.
Energy from the sun
-The best known autotrophs harness
solar energy through photosynthesis –
process by which light energy is used
to convert carbon dioxide and water
into oxygen and energy-rich
carbohydrates such as sugars and
starches, ex : plants, algae, and
photosynthetic bacteria such
as cyanobacteria.
Life without light
-Other autotrophs produce
food in the absence of light
and rely on energy within the
chemical bonds of inorganic
molecules, ex : bacteria.
When organisms use
chemical energy to produce
carbohydrates, the process
is called chemosynthesis.
B. Consumers
*Organisms that cannot
harness energy directly
from the environment
must acquire energy from
other organisms.
Heterotrophs – organisms
that rely on other
organisms for their
energy and food supply.
Heterotrophs are also
referred to as consumers.
Major types of heterotrophs
1. Herbivores – obtain energy
by eating only plants, ex :
cows, caterpillars, deer, etc.
2. Carnivores – obtain energy
by eating other animals, ex :
snakes, dogs, owls. etc.
3. Detritivores – obtain energy
by feeding on plant and
animal remains and other
dead matter called detritus.
4. Decomposers – break down
organic matter, ex : bacteria
and fungi.
C. Feeding Relationships
*Energy flows through an
ecosystem in one direction,
from the sun or inorganic
compounds to autotrophs
(producers) and then to
various heterotrophs
(consumers).
The relationships between
producers and consumers
connect organisms into
feeding networks based on
who eats whom.
Food chains
-The energy stored by
producers can be passed
through an ecosystem
along a food chain.
Food chain – a series of
steps in which organisms
transfer energy by eating
and being eaten.
Food webs
-A food web links all the
food chains in an
ecosystem together.
Food web – a network of
complex interactions
formed by the feeding
relationships among the
various organisms in an
ecosystem.
Trophic levels
-Each step in a food chain
or food web is called a
trophic level.
-Producers make up the
first trophic level and
consumers make up the
second, third, or higher
trophic levels. Each
consumer depends on the
trophic level below it for
energy.
D. Ecological Pyramids
*The amount of energy
or matter in an
ecosystem is
represented by an
ecological pyramid – a
diagram that shows the
relative amounts of
energy or matter
contained within
each trophic level in a
food chain or food web.
3 Types of Ecological Pyramids
1. Energy pyramid – pyramid
showing the relative amount
of energy available at each
trophic level.
Organisms use about 10
percent of this energy for life
processes and the rest is lost
as heat.
-The more levels that exist
between a producer and a
top-level consumer in an
ecosystem, the less energy
that remains from the original
amount.
3 Types of Ecological Pyramids
2. Biomass pyramid – pyramid
representing the amount of
living organic matter at each
trophic level. Typically the
greatest biomass is at the
base of the pyramid.
Biomass – the total amount of
living tissue within a given
trophic level.
-Biomass pyramids represent
the amount of potential food
available for each trophic level
in an ecosystem.
3 Types of Ecological Pyramids
3. Pyramid of Numbers –
pyramid showing the
relative number of
individual organisms
at each trophic level.