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Exam 3 - 2008-Spring-KEY.pdf

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PCB 4043C

Name: KEY Page 1 of 8 Instructions: --Write your name on all the pages --Make sure that all pages are attached. --Any math needed to solve a problem should be relatively simple. If not, please give your answer by showing how you would make the calculation: e.g., showing "(10+10)/4" is as good an answer as "5" (writing down an appropriate equation and clearly defining the variables, as well as indicating their values, if known, will also suffice). ECOLOGY PCB 4044 / 3063 SPRING 2008 EXAM 3 PAGE POOSNIBLE SCORE 2 16 _____Schuyler 3 18 _____Caitlin 4 16 _____Caitlin 5 16 _____Schuyler 6 17 _____Michelle 7 17 _____Craig 8 Extra space _____ _________ TOTAL 100 _____ Name: KEY Page 2 of 8 2-1. ( 10 points) Consider the following food-chain: bass – shiners – zooplankton – phytoplankton You bought an undeveloped lake (it had very clear water) 10 years ago and built your dream house on its shores. Recently, the lake water has turned green due to high concentrations of algae (phytoplankton). List two hypotheses (involving different aspects of the ecosystem) that can explain this increase in phytoplankton since you built your dream house. Provide a brief explanation (1-2 sentences) of the logic underlying ea ch hypothesis. (1) My buddies and I fished too much and reduced the density of bass, which led to a trophic cascade: fishing of bass released shiners from predation, which led to increased planktivory on zooplankton, which released phytoplankton from grazers. (2) The lake has become eutrophic because I (a) fertilize my lush green lawn with a suite of nutrients (especially nitrogen and phosphorus), and (b) my septic system might be leaking into the lake. The increase in nutrients stimulated algal production. [Note that this mechanism requires an incomplete numerical response of zooplankton, but you did not have to say this to get full credit.] 2-2. (6 points) Based on the theory of island biogeography, which island in each pair, w ould you expect to contain the greatest number of species (all else being equal)? Circle the best answer from each set. Set 1: small Large Can't be determined with available data Set 2: near Far Can't be determined with available data Set 3: near and large far and small Can't be determined with available data Name: KEY Page 3 of 8 3-1. (12 points) In the middle of the course, we noted that two competing species cannot coexist on a single limiting resource. We subsequently discussed several ways in which several potentially competing species could persist together. Please list and briefly discuss (e.g., in one sentence each), three ways in which two or more competing species can persist locally. 1. Niche partitioning (requires >1 resource); each species is limited by a different resource. 2. Habitat heterogeneity (similar to above, but the different resources are in different habitats). 3. trade-off between colonizing ability and competitive ability. 4. Better competitors are more vulnerable to predators (or parasites). 5. Better competitors are more vulnerable to disturbances. 6. Neutral theory: there is no “best competitor”; instead species are equivalent and there is a slow ‘walk’ to extinction. Extinction is balanced by s peciation. 3-2. (6 points) Capybara are semi-aquatic, herbivorous rodents native to South America. At an average of 35-75 Kg, they are the largest rodents on the planet. 25 animals escaped from a South Florida breeding facility, and there is concern that they may be persisting and even reproducing in the Everglades. List six ways (1 phrase each) that Capybara might affect native species. 1. Compete for resources (food, water, space) with native species 2. Eat native plants 3. Introduce, vector, or harbor parasites or disease that infects native sp ecies 4. Hybridize with native species 5. Alter disturbance regime, thus changing the “rules of the game” that underlie native communities 6. Indirectly alter resource supply rates, thus changing etc. 7. No effect on native species? Name: KEY Page 4 of 8 4-1. (11 points) Draw the curve of the latitudinal diversity gradient on the following graph, making sure to label both axes. Give three hypotheses for the origin of this gradient, explaining each hypothesis with 1-2 sentences High Diversity Diversity (spp. #) (Spp. # per unit area) Low 40 S 0 60 N Latitude Low Latitude High (degrees) 1. The tropical biome has been in existence longer than higher latitude biomes, leading to more time for species to evolve in or disperse to the tropics. 2. The tropical biome is larger in area than higher latitude biomes, leading to more space to fit more species (e.g., island biogeography theory), more habitat heterogeneity (more niches to fill), and larger climatically similar spaces. 3. Greater climatic stability in the tropics leads to greater specialization and more niche partitioning than at higher latitudes, where long-term climatic variability leads to the evolution of climatic “generalists.” 4. Speciation rates are higher in the tropics because of warmer temperatures and more breeding time. 5. More diversity reinforces diversity through interspecific interactions a nd close co- evolutionary relationships (high predation, increased specialization). 6. Climate change over geological time has “reset” species assemblages higher latitudes through multiple glaciations, where as the tropics have remained relatively habitable and free from massive disturbances akin to glaciations. 4-2. (5 points) Although many tropical rainforests have high tree diversity, Jordan chose to work in a tropical rainforest dominated by one species of tree, Dicymbe corymbosa. (a) Explain Jordan’s hypothesis for maintenance of Dicymbe monodominance. Dicymbe’s association with ectomycorrhizal fungi allows it to competitively exclude other species because it is able to recycle nutrients very efficiently, out competing other tree species that depend on AM or saphro
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