1. Food Chains, Food Webs, and the Transfer of Energy

2. Food Chains, Food Webs, and the Transfer of Energy
One of the main characteristics of an ecosystem is that every biotic and abiotic component of an ecosystem is directly related to many other components of the same ecosystem.
Each organism is classified according to its trophic level
Trophic level = the role of “food energy” that an organism plays in a food chain

3. Autotrophs Auto = self Troph =energy
Autotrophs are also called Producers because they produce all of the food that heterotrophs use.
Without autotrophs, there would be no life on this planet
Ex. Plants and Algae

4. Autotrophs

5. Heterotrophs Organisms that do not make their own food
Another term for Heterotroph is consumer because they consume other organisms in order to live
Ex. Rabbits, Deer, Mushrooms

6. Heterotrophs

7. Heterotrophs Consumers
1. Scavengers/Detritivores – feed on the tissue of dead organisms (both plants and animals)
Ex. – Vultures, Crows, and Shrimp

8. Heterotrophs Consumers 2. Herbivores – eat ONLY plants
Ex. – Cows, Elephants, Giraffes

9. Heterotrophs Consumers 3. Carnivores – eat ONLY meat
Ex. – Lions, Tigers, Sharks

10. Heterotrophs Consumers 4. Omnivores – eat BOTH plants and animals
Ex. – Bears and Humans

11. Heterotrophs Consumers
5. Decomposers – absorb any dead material and break it down into simple nutrients or fertilizers
Ex. – Bacteria and Mushrooms

12. Transfer of Energy
Energy cannot be created or destroyed. It can only be changed from one form to another.
When a zebra eats the grass, it does not obtain all of the energy the grass has (much of it is not eaten)
When a lion eats a zebra, it does not get all of the energy from the zebra (much of it is lost as heat)

13. Transfer of Energy
The two (2) previous examples of energy transfer show that no organism EVER receives all of the energy from the organism they just ate
Only 10% of the energy from one trophic level is transferred to the next – this is called the 10% law

14. Trophic Levels
Energy moves from one organisms to another when it is eaten
Each step in this transfer of energy is known as a trophic level
The main trophic levels are producers, consumers, and decomposers

15. Food Chains
The energy flow from one trophic level to the other is known as a food chain
A food chain is simple and direct
It involves one organism at each trophic level
Primary Consumers – eat autotrophs (producers)
Secondary Consumers – eat the primary consumers
Tertiary Consumers – eat the secondary consumers
Decomposers – bacteria and fungi that break down dead organisms and recycle the material back into the environment

16. Food Chain

17. Food Web Most organisms eat more than JUST one organism
When more organisms are involved it is known as a FOOD WEB
Food webs are more complex and involve lots of organisms

18. Food Web

19. Trophic Levels, In Food Chains:
First level is the producer (plants that produce own food energy form the sun)
The next level is the 1st order consumer = herbivores
The next level is 2nd order consumer = 1st order carnivore
The next level is 3rd order consumer = 2nd order / top order carnivore (if this animal represents the top of the food chain or web)

20. Trophic levels & numbers
Why are some organisms very common while others are rare?
Looking at trophic levels and the transfer of energy gives clues.
Which level has the most energy and which has the least?

21. Pyramid of Numbers
The number of individuals in all populations in each trophic level
Less energy available
More energy available

22. Reversed Pyramid of Numbers
Exceptions to the pattern.
For example, a big oak tree could have many insects and birds living on it and this would give a reversed pyramid

23. Biomass
The total mass of the organic matter at each trophic level is called biomass.
A pyramid of biomass shows that biomass decreases from each trophic level to the one above.

25. Pyramid of Energy Flow
Shows the relationship between consumers and producers at different trophic levels in an ecosystem
Shows the relative amounts of energy or matter contained at each trophic level
The Pyramid shows which level has the most amount of energy.

26. Pyramid of Energy Flow

28. What limits growth?
Can any populations of organisms keep growing forever?
The largest population of a species that an environment can support is called the carrying capacity.

29. Carrying Capacity
Carrying capacity is determined by the materials and energy, food chains, competition, and population density.
Intraspecific competition – Competition within the same species
Interspecific competition – competition between different species

30. Bioaccumulation
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other chemicals in an organism. 

31. Biomagnification
Biomagnification is the concentration of toxins in an organism as a result of its ingesting other plants or animals in which the toxins are more widely disbursed.

32. Videos: Pyramids: Bioaccumulation & Biomagnification:
Bioaccumulation & Biomagnification:

33. Challenges: Answer questions on handout.
Complete the investigation 1-c about DDT on page (only do numbers 1-8 on page 32).

34. Symbiosis
A close and permanent association between organisms of different species
Commensalism – a relationship in which one organism benefits and the other is not affected
Example: Barnacles on a whale
Mutualism – a relationship in which both organisms benefit from each other
Example: Birds eating pest off a rhino’s back
Parasitism – A relationship in which one organism benefits and the other is harmed
Example: Ticks on a dog