Ecological Pyramids

Learning TargetExplain why ecological pyramids are bigger on the bottom and smaller at the top.

1. What’s the ratio of guys to girls in class?2. How many guys are there for every one girl?

1. Suppose there are 19 guys and 11 girls. Guy to girl ratio = 19:11

2. To find how many guys to every one girl, divide both sides by 11:

19 : 11 11 : 11 1.7 : 1 or 2 guys : 1 girl

Good Morning!

Please get a computer and start logging on.

Navigate to the class website, and go to Links…..

Today’s Schedule

Study Hall: Library, Room 214, Room 105

• 7,996 : 4,559

• 7,996 : 4,559 4,559 4,559

• 1.75 : 1, or 2 : 1

1. Use the number totals at each level to show the ratio of producers to 1st order heterotrophs in the deciduous forest ecosystem. How many producers for every one 1st order heterotroph? Show your work!

• 831 : 58

• 831 : 58 58 58

• 14.3 : 1, or 14 : 1

2. In a desert, what is the ratio of 1st order heterotrophs to 2nd order heterotrophs? How many 1st order heterotrophs for every one 2nd order heterotroph? Show your work!

• 30 : 5

• 30 : 5 5 5

• 6 : 1

3. In a grassland, what is the ratio of 2nd order heterotrophs to 3rd order heterotrophs? How many 2nd order heterotrophs for every one 3rd order heterotroph? Show your work!

• 41 : 5

• 41 : 5 5 5

• 8 : 1

41

Each animal eats several animals from the level below.

4. Why are there fewer organisms at each level of the Pyramid of Numbers than in the levels below?

5. Calculate the percent of energy gained at each level in the Antarctic Ocean ecosystem by dividing the energy at that level by the energy at the level below it and multiplying by 100. Round off answers to the closest whole number. Show your work!

1st order heterotrophs:

2nd order heterotrophs:

3rd order heterotrophs:

784 ÷ 8,006 x 100 = 10%

86 ÷ 784 x 100 = 10.96% = 11%

7 ÷ 86 x 100 = 8.14% = 8%

6. Follow the same procedures as in step 5 to calculate the percent of energy gained at each level in the Freshwater Lake Ecosystem. Show your work!

1st order heterotrophs:

2nd order heterotrophs:

3rd order heterotrophs:

744 ÷ 7,500 x 100 = 10%

81 ÷ 744 x 100 = 11%

8 ÷ 81 x 100 = 10%

7. Why do organisms only get about 10% of the energy from the trophic level below them?

• Organisms use about 90% of the energy they get from food for life processes – moving, breathing, body heat, etc.

• Each animal only gets 10% of the food energy from the thing it ate.

• The rest of the food chains/pyramid would collapse.• Producers are at the beginning of every food chain.

Animals that eat plants would starve, animals that eat the animals that eat plants would starve, etc.

8. What would happen to an ecosystem if all the producers died off? Explain your answer.

• Wolves depend on deer for food. • Deer depend on wolves to keep them from overpopulating.

9. Apply what you’ve learned about interdependence to explain how wolf and deer populations depend on each other.

10. Positive feedback loops are when changing one thing causes a continual increase or continual decrease in another thing. Negative feedback loops are when increasing one thing causes an alternating increase and decrease of the other thing. Is the predator-prey relationship shown below a positive or negative feedback loop? Explain your answer.

• Negative feedback.• Populations going up and down instead of just up or just down.

Questions?

Using the Predator-Prey Populations graph shown below, explain how the population of prey affects the population of predators and vice versa.

http://www.bapp.org/puma-prey-lab

• When prey population goes up, predator population goes up (more food for them).

• When predator population goes up, prey population goes down (more prey getting eaten).

Positive feedback loop:• Both populations

only increase or only decrease.

Negative feedback loop:• Both populations increase and decrease.

Video: Positive & Negative Feedback Loops

http://ed.ted.com/lessons/feedback-loops-how-nature-gets-its-rhythms-anje-margriet-neutel?utm_source=TED-Ed+Subscribers&utm_campaign=d8af586ac0-2013_09_219_19_2013&utm_medium=email&utm_term=0_1aaccced48-d8af586ac0-46516589

• Animals move around. Hard to count, hard to find.

• Always changing. Animals die, born.

Constraints are things that limit how much you can do in a scientific investigation. What do you think would be some constraints in gathering the information for ecological pyramids like these?

• Other animals live there that weren’t shown in the pyramid

• Numbers are probably not exactly the same.

8. Suggest reasons why the information represented in the computer model for any one of the ecosystems studied may not truly represent that ecosystem.