Complete the following steps, create the required figure, and compile the answers to the following questions in a 2-3 page text + figures word doc report. .
1 Calculate means and standard errors for the two environments: (1) the stream food web without exotic fish (2) stream food web with exotic fish.
2 Create a single bar graph which conveys changes in the system before/after introduction of invasives. Include appropriately labeled/formated axis, legend, title, figure caption, and error bars.
3 Draw the structure of the food web under both scenarios.
4 Explain your reasoning or any assumptions you made in constructing the figure for number 3.
5 Based on this example, what are some possible effects of exotic fish on the structure of stream food webs?
6 Who does it appear that the exotic fish are feeding on? Justify your answer.
7 Trophic relationships are not the only thing that can be determined from N isotope analysis. For example, Helfield and Naiman used these data to help determine Nitrogen cycling between marine and land systems caused by salmon spawning. The authors briefly discuss other hypotheses to explain elevated foliar nitrogen and lower C: N ratios – . Briefly describe these other hypotheses and how the authors account for them as non-contributing mechanisms to increased foliar N.
8 That paper is a correlative study and there could be other factors that influence foliar N in addition to what the authors account for in the previous question. Briefly describe how you would design a manipulative experiment to test the effects of salmon-derived nitrogen on riparian zones.
9 Helfield and Naiman end with a discussion of how marine-derived nitrogen can affect stream ecosystem processes; however, they did not perform any experiments of provide any empirical data. What are some of the mechanisms by which they propose that stream productivity can be influenced by marine-derived salmon? Do you accept these ideas based on the data that is provided?
