2.1 Energy Flow in Ecosystems
By the end of section 2.1 you should be able to
understand the following:
In an ecosystem, energy flows from producers to
primary consumers to secondary and tertiary
consumers.
Food chains and food webs show the energy flow
and feeding relationships.
Each step in a food chain is called a trophic level.
Food pyramids model how energy is lost at each
trophic level in an ecosystem.
2.1 Energy Flow in Ecosystems
• Biomass is the total mass of all
living things in a given area.
(measured in g/m2 or kg/m2)
• Organisms interact with the
ecosystem by:
1.Obtaining food from the
ecosystem
2.Contributing energy to the
ecosystem
Energy Flow in Ecosystems
 Plants are called producers because they make
carbohydrates during photosynthesis.
CO2 + H2O + sunlight  C6H12O6 + O2
 Consumers get their energy by feeding on producers or
other consumers.
- Decomposers break-down wastes & dead organisms,
through the process of biodegradation.
Energy Flow & Energy Loss in Ecosystems
Methods to represent energy moving through ecosystems.
• Food chains: show the flow of energy in an ecosystem.
• Food webs: represent interconnected food chains.
They model the feeding relationships in an ecosystem
• Food pyramids: show the changes in available energy
from one trophic level to another in a food chain.
They’re also called ecological pyramids
• Each step is a trophic level
•
•
•
•
Producers = 1st trophic
level
Primary consumers
= 2nd trophic level
Secondary consumers
= 3rd trophic level
Tertiary consumers
= 4th trophic level
Food Chains
Terrestrial & aquatic food
chains
•
Consumers in a food chain can be classified as:
1.Detrivores (decomposers) - obtain energy & nutrients
from dead organisms & waste matter.
 they have their own, separate food chains & they
feed on every trophic level.
 Eg. small insects, earthworms, bacteria This dung
& fungi
2.Herbivores - primary consumers
 eat plants (producers) only
 Ex. Horse eating hay
beetle is a
detrivore.
3. Carnivores - secondary or tertiary consumers
 Secondary consumers eat non-producers (herbivores)
• Eg. Frog eating a grasshopper
Tertiary consumers eat secondary
consumers
• also called top predators, top
carnivores or top consumers
• Eg. Lions eating humans
4. Omnivores - consumers that eat both
plants & animals
• Eg. include humans and bears

•
Food Webs
• Most organisms are part of
many food chains.
• Arrows in a food web
represent the flow of energy
and nutrients.
• Following the arrows leads
to the top carnivore(s).
This food web represents a terrestrial
ecosystem that could be found in
British Columbia.
Food Pyramids
 Energy enters at the first tropic level (producers), where
there is a large amount of biomass & therefore a lot of
energy
• It takes large quantities of organisms in one tropic level to
meet the energy needs of the next trophic level.
• 80% - 90% of energy taken in by consumers is used in
chemical reactions in the body, or is lost as heat energy.
• The amount of life an ecosystem can sustain is based on
the bottom level of the ecological pyramid, where
producers capture energy from the sun.
• Lower trophic levels have much larger populations than
upper levels.
• This shows the importance of maintaining large, biodiverse
populations at the lowest levels of the food pyramid.
Take the Section 2.1 Quiz