Ecosystems – Energy flow and nutrient cycling an

introductory investigation

Background:

Ecosystems are made up of two major components: the biotic or living community, and the aboitic or nonliving world. The abiotic realm provides the nutrients and energy required by all life, while the biotic realm harnesses and transfers these materials. These materials flow through food chains finally being released back into the environment. In this lab we will first investigate the food web of DenaliNational Park. DNP is a 24,585 km2 park in interior Alaskawhich is made up of tundra and northern coniferous forest, or taiga. We will complete our analysis of the biotic and abiotic interactions of an ecosystemwith an attempt to determine the energy flow through the ecosystem.

Facts you need to know:

1)1 km2 of taigafixes3.4x 109 kilocaloriesof solar energy per year through photosynthesis.

2)For the purpose of this lab assume ecological efficiency of 10%.

Warm up: Complete in full sentences on white lined paper.

Autotroph-

Carnivore-

Detritivore-

Herbivore-

Heterotroph-

Ommivore-

Trophic level-

Procedures:

1)Observe the Denali ecosystem worksheet.

2)Obtain a trophic pyramid worksheet and label the boxes autotrophs, primary consumers, secondary consumers, and tertiary or top consumers.

On the trophic pyramid worksheet write the name of the organism in its appropriate trophic level. Be sure to keep organisms which feed off others above the organisms they feed on.

3)Once you are convinced you have described the complete food web, draw the source of energy for the food web. Also be sure to determine where the detritivores (fungi) would be found.

4)Using the information above, place an estimate of the total available kilocalories per trophic level in each appropriate region of your food web. Start with 3.4 X 109 kilocalories at the first trophic level. Remember we are working with a 10% ecological efficiency.

Analysis: Answer the following in complete sentences on this paper

1)All food chains and food webs have more biomass and individuals in the lowest trophic level. Why does this make perfect sense?

2)What are the likely abiotic components of the DNP ecosystem?

3)Suppose a pollutant has killed off the aquatic plants of the ecosystem, what other organisms would be affected?

4)Describe what occurs to the energy as you move up trophic levels.

5)Describe what likely occurs to the matter in this ecosystem.

6) Describe why ecological efficiency tends to be so low in ecosystems.

( Hint view figure 3-16 pg. 47)

7) Describe the link between aerobic respiration and photosynthesis.