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.

What causes the numbers of individuals in a population to decrease from producer to top level consumers?

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

Pyramid of energy example -Students jot down this pyramid of energy in notes (don’t need pictures). Important to include trophic level labels (producer, primary consumers, etc.) -The “J” stands for joules. Joules are a measure of energy. Calories are another measure of energy. -Ask students: Quantitatively, what do you notice about how the amount of energy decreases each step through the food chain? -Notice that each trophic level generally gets ~10% of energy from previous trophic level. This is called the 10% rule.

10% Rule in Ecology An average of only 10% of the energy in one trophic level is passed to the next trophic level. -Students copy this definition -Ask students to think: why do you think this happens? Think of the game from yesterday. (go to next slide as you talk about this)

10% rule... 10% 90% lost as heat

10% rule diagrams... 10% 90% lost as heat

10% rule diagrams... 10% 90% lost as heat

How much energy is at each level? 1000 Cal ? Cal

How much energy is at each level? 9 Cal as heat 1000 Cal 100 Cal 10 Cal 1 Cal 90 Cal as heat 900 Cal as heat

10% Rule Why do you think only 10% of the total energy from 1 trophic level is passed to the next?

3 Reasons for decrease in available energy Energy is “used up” for daily life activities. Not all organisms that die are eaten by animals in the next trophic level. Not all parts of an organism are eaten and digested for energy. Show just the heading and elicit student responses. When students have given reasons, continue to show 3 reasons for them to copy down.