1. Energy Flow through
Ecological Systems
The other balance of life…

2. Photosynthesis
Again, the equation for photosynthesis
is:
6 CO2 + 6H2O + light energy C6H12O6 + 6 O2
This equation leaves out important
details:
1. Where does the O2 gas come from?
2. How is light energy converted
into chemical bond energy?

3. Photosynthesis
Why is it so important to life?
 It is estimated that 99% of the energy used by
living cells comes from the sun!!!!!
 Incorporation of sunlight into chemical bonds
occurs through the process of photosynthesis
 "Invented" by cyanobacteria about 2 billion years
ago
 Oxygen is a waste product of photosynthesis
 All oxygen in atmosphere is believed to originate
from photosynthesis

4. Photosynthesis
Also…...
 Photosynthesis begins the carbon cycle
by fixing CO2 (carbon dioxide in the
atmosphere)
 The oxygen released as a by-product has
a major impact on the biosphere.
Today's atmosphere would not have 21%
oxygen if not for photosynthesis.

6. Energy Flow Charts
Your plot receives 10,000
kcal/m2/day of energy
Tell us where it all goes!!!
On butcher paper create an Energy Flow
Diagram from a simple imaginary food
chain, which demonstrates how this
energy enters and exits your plot.

7. What scientific laws
apply to energy?
 First and Second Laws of
thermodynamics
 First law: energy is neither created
or destroyed!!! General accounting…
 Second law: every step of energy
transformation and flow through a
system = gradual loss of the ability
to do work.

8. What happens to all of
that energy anyway?
 Equator most light--- poles about ½ the amount
 1/3 reflects off clouds, snow fields bounces
back to space
 1/3 warms sea/land
 1/4 absorbed in evaporation drives water cycle
 1% - 2% of light striking a forest is used by all
other living beings.
Equivalent only 1/5 of the gasoline you put in
your car gets you to your destination…..bummer
hey….

10. Trophic Levels

11. Effects of Lindeman’s Efficiency
(10% Rule)
 Top predators are sensitive to changes in the
energy flow of an ecosystem
 Cannot have more than 4 or 5 levels on a trophic
pyramid. Why?
 The amount of energy and space needed to feed
animals on a higher trophic level would be larger
than the amount of energy expended to forage for
it

12. Effects of Lindeman’s
Efficiency (10 % Rule)
 Omnivores (i.e., bears, humans, raccoons,
opossums, coyotes, etc.) can switch trophic
levels depending on the food sources that
are available
 Eating at lower trophic levels can support
more members of a population in an
ecosystem/environment

13. Humans and Energy Flow
 Humans are omnivores
 Humans use approximately 40% of the net
primary production on land
 Net primary production: the amount of available
energy that is produced in photosynthesis (after
plants use what they need for survival)

14. Energy Flow and Eating
Habits
 Meat eating (higher on the trophic pyramid) uses
more energy than eating veggies
 90% of the grain that we grow is used to feed
livestock
 100 kg of grain can feed:
 10 kg of cow and 1 kg of steak eating people
 10 kg of grain eating people (10x more)

15. A simple food web……….

16. Implications
 We observe this dynamic balance of energy
flow at all levels of scale from the
ecological system to the individual
organism.
 Also, this is the algebra with which we can
understand the consequences of our actions.