Warm-up
Use complete sentences to describe how
the number of species in lower trophic
levels compares with the number of
species in higher trophic levels. Explain a
reason for why this occurs.
1
What causes the numbers of individuals in a population
to decrease from producer to top level consumers?
2
Number of organisms in a
trophic level compared with total
energy in a trophic level
Think about how many individual insects
could be supported by one individual
tree…
We usually compare trophic levels by how
much total energy the trophic level
contains rather than the total number of
organisms in a trophic level
3
Pyramid of energy example
4
10% Rule in Ecology
• An average of only 10%
of the energy in one
trophic level is passed
to the next trophic
level.
5
10% rule...
10%
6
10% rule diagrams...
10%
7
10% rule diagrams...
10%
8
How much energy is at each
level?
? Cal
? Cal
? Cal
1000 Cal
9
How much energy is at each
level?
1 Cal
10 Cal
100 Cal
1000 Cal
10
10% Rule
• Why do you think only 10% of the total
energy from 1 trophic level is passed to
the next?
11
3 Reasons for decrease in
available energy
1. Energy is “used up” for daily life
activities.
2. Not all organisms that die are
eaten by animals in the next
trophic level.
3. Not all parts of an organism are
eaten and digested for energy.
12