At the end of this chapter learners should be able to:
Define ecosystem and other important terms
Draw and label a food web
Discuss the food pyramids and energy pyramids in details
Discuss biomass in details
Explain the energy transfer in the ecosystem.
An ECOSYSTEM is all the different organisms in
the world living together in a PARTICULAR
Our own bodies are homes to tiny
All the ecosystems combined together make up the BIOSPHERE
An ecosystem is an environment in which plants
(flora) and animals (fauna) live.
Ecosystems survive through the interactions
between plants and animals and an example of this
is what are referred to as food chains and food
Without these interactions, ecosystems risk
breaking down and could be destroyed - we will
look at this in more detail when we look at
ecosystems under threat.
The collection of organisms in
an area along with the
important environmental factors
Eg ocean ecosystem
A population is the number of
organisms of the same species
living in a habitat
All the animals and plants
living in an ecosystem
The area where animals and
Eg ocean habitat
Or.. More specific Coral
The level occupied by a consumer in a food
chain is referred to as a feeding or TROPHIC
Primary consumers occupy the 1st trophic
level; secondary consumers occupy the 2nd
trophic level, and so on.
A food chain is a linear sequence of links in a food web starting from a species that are
called producers in the web and ends at a species that is called decomposers species in
the web. A food chain also shows how the organisms are related with each other by the
food they eat. A food chain differs from a food web, because the complex polyphagous
network of feeding relations are aggregated into trophic species and the chain only
follows linear monophagous pathways. A common metric used to quantify food web
trophic structure is food chain length. In its simplest form, the length of a chain is the
number of links between a trophic consumer and the base of the web and the mean chain
length of an entire web is the arithmetic average of the lengths of all chains in a food web
What happens if a link in the food chain is broken?
The interrelationship between many food chains
is called a food web.
Biomass is an estimate of the amount of matter in a
given population of organisms. Biomass for
trophic levels is compared in a biomass pyramid.
A biomass pyramid shows how the quantity of
in living things changes along a food chain.
Pyramid of Biomass
The base of the pyramid
represents the matter in
producers. The next
level shows biomass of
primary consumers and
Biomass decreases as you go up the pyramid
An energy pyramid shows the total energy in
trophic levels and how that energy is lost
along a food chain.
Organisms that use the organic matter of dead
plants and animals are called decomposers.
They release digestive enzymes to break down
organic matter and then absorb the products
Decomposers include fungi and bacteria.
Decomposers do not fit readily into one trophic
So where does all the
energy go if not 100%
from one organism to
Energy losses in food chains
1. Some parts of the organism not eaten
2. Some parts are not eaten but cannot be digested and are
therefore lost in feaces
3. Some of the energy is lost in excretory materials, such
4. Some energy losses occur as heat from respiration and
directly from the body to the environment.
Why would energy losses be higher in birds and mammals
compared to reptiles/amphibians?
1. Limits to 4/5 organisms
because insufficient energy is
available to support a large
enough breeding population at
trophic levels higher than these
2. Total mass of organisms in a
particular place (biomass) is less
at higher trophic levels
3. Total amount of energy
stored is less at each level as
one moves op a food chain
How does the relative
inefficiency of energy
trophic levels affect