Biology 12

446 MHR • Unit 5 Population Dynamics

be available to the secondary consumers that eat

caterpillars. Approximately one third of the energy

the caterpillar obtains is used in its own cellular

respiration (providing energy for locomotion,

maintaining body temperature, and other body

processes), and therefore lost to the ecosystem.

In fact, only about one sixth of the energy is

incorporated into new caterpillar tissue — tissue

that can be eaten by secondary consumers.

This energy loss (and its related unusable heat)

occurs between all trophic levels in a food web (see

Figure 13.20). Although the efficiency with which

energy is transferred from one level to the next

varies among different types of organisms, it

usually ranges between 5 and 20 percent. In other

words, roughly 80 to 95 percent of the potential

energy available at one trophic level is not

transferred to the next one. This pattern of energy

loss is often illustrated as a pyramid of

productivity(see Figure 13.21 on page 448).

Figure 13.19Why is so much energy lost as waste from a

caterpillar?

The next MiniLab will help you understand

pyramids of productivity by examining three

typical food chains.

plant material eaten

by caterpillar

feces

growth

cellular

respiration

100 J

33 J

67 J

200 J

100% energy to environment

photosynthesis

Earth Sun

producers

herbivores

decomposers

organic wastes/dead tissue

respiratory heat loss

loss = 23.8% loss = 76.2%

top carnivores

carnivores

loss =

21.4% loss 67.2%=

loss =

20.4% 16.2% loss = 63.4%

1 – 2% solar energy

5.5%

11.4%

loss = 23.5% loss = 71%

heat (energy) loss to environment

Figure 13.20Why is the

respiratory heat loss of

consumers higher than

that of producers? Note

that it is highest for

top-level carnivores.