1. Energy Flow in an ecosystem

2. Energy flow Simplistically: This pattern of energy flow among different organisms is the TROPHIC STRUCTURE of an ecosystem. heat Producers Consumers Decomposers heat

3. It is useful to distinguish different types of organisms within these major groups, particularly within the consumer group. Consumers

4. Terminology of trophic levels We can further separate the TROPHIC LEVELS, particularly the Consumers: Producers (Plants, algae, cyanobacteria; some chemotrophs)--capture energy, produce complex organic compounds Primary consumers--feed on producers Secondary consumers--feed on primary consumers Tertiary consumers--feed on secondary consumers

5. More trophic levels: Detritivores--invertebrates that feed on organic wastes and dead organisms (detritus) from all trophic levels Decomposers--bacteria and fungi that break down dead material into inorganic materials

6. Alternate Terminology

7. Together, these groups make up a FOOD CHAIN E.g., grass, rabbit, eagle CarnivoreHerbivoreProducer

8. Carnivores Carnivores can be further divided into groups: quaternary carnivore (top) tertiary carnivore secondary carnivore primary carnivore The last carnivore in a chain, which is not usually eaten by any other carnivore, is often referred to as the top carnivore.

9. Food chains

10. Problems Too simplistic No detritivores Chains too long

11. Rarely are things as simple as grass, rabbit, hawk, or indeed any simple linear sequence of organisms. More typically, there are multiple interactions, so that we end up with a FOOD WEB.

13. Energy transfers among trophic levels How much energy is passed from one trophic level to the next? How efficient are such transfers?

14. Generally speaking we use the rule of 10% This means that only 10% (on average) of the energy in one trophic level gets passed up to the next trophic level. This means that about 90% of the energy is left behind? Why does this happen? Discuss this with your partner for a couple of minutes and we will share your answers in class.

15. Remember that energy = work + heat (and other wasted energy) Energy transfer is never 100% efficient. The efficiency of a plant converting solar energy to stored sugars is only 1-2%. Herbivores on average only absorb and use about 10% of the total plant energy they consume. The rest is lost in metabolic processes. A carnivore’s efficiency is also only about 10%.