Food Chains, Food Webs, and the Transfer of Energy

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: • https://www.youtube.com/watch?v=wGfOoRrICto&list=PLYwJPbm-kWknXB_BE2SyrMpBDv9NeHMeZ • Bioaccumulation & Biomagnification: • https://www.youtube.com/watch?v=TZk6vcmLcKw

33. Challenges: • Answer questions on handout. • Complete the investigation 1-c about DDT on page 30-32 (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