BI 325 Example test Name KEY

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1 NOTE: THESE ARE EXAMPLE QUESTIONS PULLED FROM PAST TESTS. ACTUAL TEST LENGTH, COVERAGE AND POINT DISTRIBUTIONS MAY VARY. QUESTIONS RELATED TO WATER USE MAY NOT BE COVERED, DEPENDING ON HOW FAR WE GET ON FRIDAY. Part A. Multiple multiple choice. (29 points) Circle the correct choices for each question, remembering that none, one or more answers could be correct for each. Correct answers are bolded. Make sure you know the reasons why other answers are incorrect. Can you rewrite them to make them correct? 1. In the absence of fertilizers, farmers on Madagascar can only farm a given site for 4-5 years, after which the nutrient levels in the soil cannot support further agriculture. At this point the farmers must clear a new area. It is this sort of 'shifting agriculture' that poses the greatest threat to remaining rainforests on the island. To improve their crop productivity, farmers have experimented with different fertilizers. The results of a typical fertilization experiment are shown below in Fig.2. Crop yield Productivity (g C/m2*yr) C +N +P +N+P Treatment Fig. 2. Results of fertilization on crop yield (mean ± standard deviation). C is control (no fertilizers added); +N is added nitrogen; +P is added phosphorus; +N+P is both nitrogen and phosphorus added. a. Based on the results, above, phosphorus is the only nutrient limiting plant growth at this site. b. Based on the results, above, it is likely that many of the original plant species at this site had mycorrhizal mutualisms. c. If phosphorus in fertilizers leached into adjacent streams and lakes, it could cause large increases in phytoplankton growth because P is generally the most limiting nutrient in freshwater ecosystems. d. A dramatic increase in phytoplankton productivity would most likely lead to dramatic increases in fish production as well. 2. Global average temperatures have increased about 1 o C over the past century and are expected to increase another 2-4 o C, because of elevated CO 2. a. In areas not restricted by water availability, this temperature increase would increase actual evapotranspiration (AET). b. In areas not restricted by water availability, any increase in temperature would likely cause increased stomatal closure in plants, greatly favoring C4 species. Not covered yet, but not true. c. In areas not restricted by water or nutrient availability, both net primary production (NPP) and decomposition would be expected to increase with the projected changes in temperature. d. The increase in NPP with increasing temperature would be sufficient to lead to long-term net sinks of excess atmospheric CO 2. 1

2 6 Water vapor pressure (kpa) 5 4 Habitat Temperature (degrees C) 100%RH 75%RH 50%RH 25%RH Habitat 2 3. Given the above diagram showing where two different habitats fall in the relationship between the water holding capacity of air and temperature, which of the following statements are accurate? Material not covered yet. a. Vapor pressure deficit (VPD) is greater in habitat 1 than in habitat 2. b. Organisms with thick, water impermeable membranes have a greater selective advantage in habitat 1 than habitat 2. c. Ectothermic organisms relying on vapor limited evaporation face a quandary in that VPD is lower at low temperatures but because of Q10, their metabolic rates are also much lower at low temperature. d. The quandary mentioned in c. is logically consistent with several observed facts, including the presence of nasty toxins in the skin of some northern salamanders (i.e., chemicals toxic to predators of those salamanders) and the greater abundance and diversity of amphibians in tropical rainforests than in temperate and or boreal forests. 4. In deserts of Arizona, a common tree is Prosopis (mesquite), which has very deep roots that can reach the water table (up to 150' deep!). Plants with this type of rooting system are called phreatophytes. Contact with the water table allows Prosopis (and other phreatophytes) constant access to water. There is a phenomenon with Prosopis in which water flows from wet soil very deep in the ground, into a plant's deep roots, then into a plant's shallow roots, and from the shallow roots into the very, very dry surface soil. Which of the following statements help explain how such a flow could take place. Material not covered yet. a. The main concept that explains this phenomenon is that countercurrent flow allows water to flow from lower to higher water potential. b. This phenomenon only occurs at night because dew condensing on the leaves flows down its water potential gradient through the plants xylem and out into the soil. c. This phenomenon occurs because the matric potential of the upper soil layer is more negative than the solute potential of the adjacent roots and these roots have a lower water potential than the deep roots and the deep roots have lower water potential than the adjacent groundwater. d. Without the hydrogen-bonding properties of water, this flow could not take place. 5. You re traveling among the Auracaria forests in the central highlands of Chile when the thought suddenly strikes you, Wow, these trees have a lot of the same adaptations as the conifers in Western Washington. From your backpack, you pull out your copy of Molles (which you carry with you on all your travels), and confirm that indeed the climate diagrams for the Chilean temperate forests are quite similar to those from around Bellingham. But you 2

3 also know that the Auracariaceae is a completely different plant family from Pinaceae, in which most of our local conifer species are found. a. Clearly the Chilean species are the same ecotype as the Western Washington species despite being in different families. b. Clearly this situation arose from phenotypic plasticity of species within the Pinaceae. c. Clearly convergent evolution could have played a role in driving the morphological similarities. d. You have no bloody idea because you sold your copy of Molles immediately following ecology class. B. Graphing and short answer (31 points) 7. (5 points) Briefly describe the relationship between limiting resources, allocation tradeoffs, fitness, and natural selection. There are many configurations for this, but here it is in a nutshell: Limiting resources force tradeoffs in allocation of those resources (e.g., defense, more growth, reproduction) within an individual. Efficiency of allocation of limiting resources determines fitness (contribution to gene pool of future generations; i.e., includes reproduction as well as survival!) under different natural selection pressures. A given allocation strategy might work well in one situation under one suite of selection pressures, but not well in another hence tradeoffs it s tough to do everything well with limiting resources. Note: Differences in fitness are what happen as a result of different strategies under different selective pressures, not the other way around. 8. a) (8 points) Draw the relationship between AET and NPP on the graph below. On average NPP AET b) (12 points) Briefly describe why this relationship exists in terms of both physiological ecology and ecosystemlevel feedbacks. Actual evapotranspiration AET depends on both temperature and moisture and so indicates good conditions for plant growth and for the microbes that decompose organic matter. High AET means that temperatures are warm and that there is plenty of water to be evaporated and/or transpired. Low AET could result either because of low temperatures or because of low water availability even at high temperatures. At a physiological level, warmer temperatures lead to higher plant growth because metabolic rates generally increase with temperature. Q 10 = ~2, meaning that biochemical reactions rates roughly double with a 10 degree increase in temperature. More water means that stomata can stay open to allow CO 2 to enter the leaves, allowing greater photosynthetic rates. Plants still lose a lot of water in this case, but it doesn t matter because there s lots available. Lack of water means plants need to close stomata to keep from losing more water by transpiration than they re able to get out of the soil. At the 3

4 whole organism level, low water often means more allocation to roots and less to shoots (stems and leaves), slowing overall growth. NOTE: you needed to address both the temperature and water issues for full credit. At the ecosystem level, higher AET means higher decomposition rates, which increases nutrient availability to plants. Because nutrients (particularly N) frequently limit plant growth, greater nutrient availability typically increases NPP. Physiologically, the more N that can be invested in building Rubisco in the leaves, the higher the photosynthetic rate of a given leaf. C. Essay. Answer one of the following two questions (20 points each). Be sure your answers are clear, concise and complete. If you don t know an exact answer, show me that you know how to think about the important things to consider to find an answer. If the question says critically evaluate, then that means discuss both supporting and contradicting evidence. 7. (20 points) Critically evaluate the statement Give me a tanker of iron and I ll give you the next ice age. Explain this statement, including its relevance to ocean ecosystem productivity, nutrient limitation, the global C cycle and historical levels of atmospheric CO 2. What component of the C cycle does this neglect and how might that influence the potential of oceans to sequester excess CO 2 from the atmosphere? This statement was made in suggesting that iron-limited regions of the open ocean have large potential to sequester CO 2 from the atmosphere if phytoplankton photosynthesis and growth can be increased by iron fertilization. One hypothesized feedback mechanism leading to the patterns of CO 2 and temperatures in the long-term (650,000 year) ice core record goes as follows: changes in Earth s orbit (Milankovitch cycles) lead to changes in solar input. A large decrease in solar input during an interglacial period could start cooling, leading to more build-up of continental ice sheets, leading to lower sea levels. That would expose large areas of bare sediments at the ocean margins as sea level falls. Those sediments could be easily eroded by wind, and deposited in the open ocean, where the iron the sediments contain would lead to increased phytoplankton growth. That phytoplankton growth would then decrease atmospheric CO 2 cooler temperature more ice lower sea level more wind deposited iron more phytoplankton growth, and so on, in a positive feedback cycle that would greatly amplify the original signal arising from the changes in solar input. Hence the reference to ice ages in the original quote. Critical evaluation: Could a tanker of iron really do this? Well, probably not just a tanker full (yes, there was hyperbole in the original quote). But, indeed, large scale iron fertilization experiments suggest that phytoplankton growth can be increased greatly with iron inputs. Would this lead to greater CO 2 sequestration in the long term? That depends on the fate of that phytoplankton growth. If the new phytoplankton are quickly eaten by zooplankton and fish, with the majority of carbon being re-released as CO 2 following consumer respiration, then no. This respiration is the important part of the C cycle that the original statement neglects. If however, a large proportion of the additional phytoplankton growth sinks into the deep ocean as sediments (the biological pump ), it will be effectively sequestered from the atmosphere for thousands to millions of years. In that case, iron fertilization could lead to greater net uptake of atmospheric CO2. The jury is still out as to what happens and experiments are underway to see which way the balance lies. 8. (20 points) One biome described in your book that we briefly discussed in class is the tropical dry forest, in which the trees lose their leaves in the dry season. Though we have mentioned a few times that cacti grow in deserts but not in forests, as it turns out, there is a large cactus, Opuntia excelsa, that grows in some tropical dry forests of Mexico. Using the climate diagram for tropical dry forest, below, and the tradeoffs inherent in C3 and CAM photosynthesis, explain how Opuntia excelsa might be able to persist in the midst of all those trees. precipitation temperature Wet Dry 4

5 In the wet season (middle of May middle of Oct.), the leaves are on the tree which use C3 photosynthesi; the cacti, which use CAM, are shaded and have relatively low photosynthesis or growth. They can take up water and store it for the dry season in their succulent stems, however. The trees(c3) have the growth advantage because there are no water restrictions on photosynthesis. (5 points) In the dry season (Nov. - May), the trees lose their leaves and become dormant to prevent excessive water loss and/or photorespiration. This allows light to reach the cacti and they can then photosynthesize using CAM photosynthesis. (5 points) The fundamental tradeoff is between the fast, competitive growth rates of the trees using the relatively energy efficient (but water inefficient) C3 photosynthesis during the wet season and the slow, energetically expensive, but water efficient, growth of the cacti using CAM photosynthesis in the dry season. Various descriptions of how CAM allows a plant to use water so efficiently (e.g., stomata open at night when VPD is lower than in day, etc.) compared to C3 plants(stomata open during the day, photorespiration) helped strengthen your arguments. However, I wasn t looking for extensive biochemical detail here; many people spewed all they knew about biochemistry, but missed the main point of the question, which is about tradeoffs (6 points). Light availability is critical to this tradeoff: the cacti need high light for photosynthesis they can t grow in the shade of the trees. If the trees weren t deciduous in the dry season, the cacti wouldn t make it. (4 points) 9. (20 points) Anadromous fish like salmon must go from fresh water where they hatched to salt where they spend the majority of their adult lives. Some of this material lwas not covered yet, but I provide the answer to give you the feel for it what I m looking for. a. (13 points) Explain the physiological and behavioral changes that young salmon must go through in order to maintain their water balance when going from fresh to salt water. In your description make sure that you first define the major components of the fishes water balance and show that you can correctly use the terms hyperosmotic and hyposmotic. Salmon in fresh water are hyperosmotic relative to the water, and so they suffer from water gain and ion loss. To counter these problems, freshwater fish produce lots of dilute urine, obtain ions via their food and via active transport by chloride cells in their gills, and they don't drink. Salmon in salt water face the opposite problems, since they are hypoosmotic relative to their environment. Thus, they tend to lose water. To counter this problem, these fish must drink large amounts of water, but this also elevates ion concentrations. Thus, to get rid of excess salts, salmon in salt water use chloride cells to actively transport salts out of their gills (a reversal of function of these cells compared to what they do in fresh water). In addition, they excrete salts in their urine, which is not very concentrated, but is more concentrated and of much lower volume than in freshwater salmon. b. (4 pts.) Why are these changes necessary in terms of the water potential of the fish and their surroundings? In fresh water, salmon have lower water potential than the surroundings, due to their relatively high solute concentrations. Since water flows from high water potential to lower water potential, it tends to enter the bodies of the salmon. In salt water, salmon have a higher water potential than their surroundings, due to the high concentration of solutes in salt water. Thus, water tends to flow from salmon to their surroundings. c. (3 pts.)are these changes an example of adaptation or acclimatization? Explain why. The physiological changes that individual salmon make as they move from fresh water to salt water are examples of acclimatization. These changes do not reflect a change in the genetic makeup of individual salmon. While it is true that the ability to make the changes is an adaptation, the actual changes them selves are acclimatization. 5