1. Energy Flow in Ecosystems (#6)
Food Chains, Food Webs, and Energy Pyramids

2. 1. Where does our energy come from?
The sun!
A. Most life on earth depends on photosynthetic organisms that can convert the energy from the sun to a usable source of energy.
B. The rate at which the sun’s energy is converted to organic molecules (food) is known as primary productivity.

3. 2. Producers and Consumers
A. Organisms that first capture energy are known as producers
Plants, algae, and some types of bacteria
B All other organisms in the ecosystem are known as consumers-organisms that consume other organisms to obtain energy
Bugs, cows, people, mushrooms, and some types of bacteria

4. Trophic Levels
3. Trophic levels are levels that organisms are assigned to based on the organism’s source of energy
Primary
Consumer
Secondary
Consumer
Sun
Producer

5. 4. Food Chains
A. The path of energy through the trophic levels of an ecosystem is called a food chain.
B. First level: Producers
C. Second level: Herbivores – organisms that eat only plants
D. Third level:
i. Carnivores – animals that only eat other animals
ii. Omnivores – animals that eat both plants and animals
iii. Detritivores – organisms that obtain their energy from organic wastes and dead organisms
a. Bacteria and Fungi are detritivores that cause decay, so they are known as decomposers

6. Carnivore
Herbivore
Detritivore
Decomposers
Omnivore

7. Food Chain- Draw and label on your notes!
Algae
Killer Whale
Krill
Leopard Seal
Cod

8. Food Webs
5. In most ecosystems, the flow of energy isn’t a simple straight line, like a food chain
6. There are multiple, complex interactions that involve several trophic levels
7. This complex, interconnected group of food chains is known as a food web

9. Honey mesquite (pods eaten by beetles)
Chihuahuan raven
Honey mesquite (pods eaten by beetles)
Pronghorn antelope
Gambel quail
Jackrabbit
Desert tortoise
Coyote
(top carnivore)
Prickly pear cactus
Long-tail weasel
Roadrunner
Kangaroo rat (seed eater)
Mojave rattlesnake
Red spotted toad
Texas horned lizard
Mexican whiptail lizard

10. 8. “Loss” of Energy in a Food Chain
A. As energy moves through the trophic levels, some of the energy is “lost” as heat (we give off heat as we “burn” our food)
B. Only about 10% of the energy is passed from one trophic level to the next

11. Pyramid of Energy Heat 0.1% Consumers 1% Consumers 10% Consumers
100% Producers
Parasites, scavengers, and decomposers feed at each level.

12. Pyramid of Numbers Fox (1) Birds (25) Grasshoppers (250)
Grasses (3000)

13. 1 kilogram of human tissue
Pyramid of Biomass
1 kilogram of human tissue
10 kilograms of beef
100 kilograms of grain
Biomass: The dry weight of tissue and other organic matter found in a specific ecosystem or organism

14. Biomagnification
10. Biomagnification is the increase in concentration of a substance that occurs in a food chain because:
A. It is not easily gotten rid of or broken down into something else (persistence) in the environment
B. Low rate of digestion/absorption/excretion in animals usually because the substance doesn’t dissolve well in water.

15. 10. Biomagnification C. Food Chain Energy
As more animals eat animals from beneath their trophic level, that chemical substance accumulates in their bodies, usually in fat.
11. Example:
A. Zooplankton have small quantities of mercury they pick up in water over their life time
B Anchovies eat zoo plankton, and keep the total mercury eaten from ALL the zoo plankton they consume. Mercury makes anchovies smaller

16. 11. Example of Biomagnification
C. Tuna eat anchovies- since the anchovies are smaller, tuna have to eat more fish to get all their nutrients. Tuna keep ALL the mercury that was stored in each anchovy they eat!
By the time we measure the mercury concentration in the fish it’s dramatically more concentrated than the concentration in the original zoo plankton.
D. Other examples of chemicals in biomagnification:
DDT (pesticide)
PCB (used as a dielectric, coolant fluid, PVC Pipe, as well as other construction materials)
Arsenic