Practice Exam Key #7 Essay

Homework 7 Practice Exam 7
Tuesday, November 27

1.) In some orchid species, flowers look and smell like a female wasp. Males will visit the flowers and try to copulate with them. In the process, they get dusted with pollen. What is the nature of this interaction? (competition, consumption, commensalism, parasitism, mutualism) Explain your logic. Key: Sample answer Parasitism--the wasp wastes time and energy copulating with the orchid, while the orchid gets pollinated. There is a fitness cost to the wasp, and a fitness benefit to the orchid. Grading rubric For full credit (2 points): The answer must be parasitism and the explanation must clearly articulate the fitness cost and fitness benefit to the two parties. If one part of the three parts of the full-credit answer is incorrect or missing, award 1 point. If two or all three parts of a full credit answer are incorrect or missing, award 0 points.

2.) If a fire burns a grassland, it may kill woody species that have growing tissue aboveground, but it won't kill grasses and forbs because they can re-sprout from underground tissues. Based on this information, does a grassland fire qualify as a disturbance relative to a) any woody species present, and 2) the grasses and forbs? Answer yes/no for a) and b). In each case, explain your reasoning. Key: Sample answer a) Yes--it removes the aboveground biomass and if it kills the entire plant, it removes the belowground biomass as well. b) Yes--it removes the aboveground biomass, even if the plants are quickly able to resprout. As a side note, removing even dead and dry grasses and forbs has a huge impact on the animals present, as they have little to eat and nowhere to hide until regrowth occurs. Also, the presence of dead and decaying vegetation affects soil moisture and humidity and ties up nutrients. So burning them off changes the environment for the plants present. Grading rubric For full credit (2 points): Both parts should be yes, and the explanations should be clear and based on sound reasoning. If one part of the four parts of the full-credit answer is incorrect or missing, award 1 point. If two or more parts of a full credit answer are incorrect or missing, award 0 points.

3.) After clearcutting and replanting a site, foresters in the Pacific Northwest will sometimes fertilize with

urea or biosolids (both are good sources of N; as an aside, biosolids are produced by municipal sewage treatment plants). a) Why is this treatment particularly effective after a clearcut? b) Compared to a clearcut, would it be more, equally, or less beneficial to fertilize after a fire that removed the same amount of biomass? Key: Sample answer a) Clearcutting removes all of the nutrients present in wood; fertilizing is a way to replace these nutrients. OR a) After replanting, young trees have lots of sunlight and can grow quickly--so they can benefit from additional nutrients more than mature trees can. b) Perhaps less beneficial, as the ash and charcoal left after a fire contains nutrients that can fertilize the soil. Grading rubric BE ALERT for alternative answers that are valid enough to get full-credit. For full credit (2 points): a) Answer must give a biological compelling reason why fertilization would benefit trees after biomass removal by clearcutting--that is, the benefit must be based on the results of clearcutting. b) Answer must be based on the contrast in remaining nutrient (something relevant to fertilization) between biomass removal by clearcutting v fire. If either a) or b) is incorrect or missing or represents "blather"--meaning that in your judgment, the author did not have a reasonable idea of how to approach the problem--award 1 point. If both parts are incorrect or missing or consist of "blather," award 0 points.

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