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Exam 2 - 2010-Spring-key.pdf

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PCB 4043C

Your code: KEY Page 1 of 12 THIS KEY GIVES ONE SET OF POSSIBLE ANSWER. OTHER OPTIONS WERE POSSIBLE AND MAY HAVE RECEIVED CREDIT. (N=65 STUDENTS TOOK EXAM ) GENERAL ECOLOGY (PCB 4043) Spring 2010 EXAM 2 • Write your code on all the pages • Make sure that all pages are attached. • You may not use calculators, cell phones, brain chips, or other electronic aids. The math needed to solve a problem should be relatively simple. If you can't do the math, just show what needs to be calculated (e.g., "answer = .5 x .3") • If you get hung up on a problem, skip it; return to it after you’ve answered the “easy” problems. PAGE PPOSINBSLE SCORE 1 2 _____ 2 6 _____ 3 8 _____ 4 8 _____ 5 10 _____ 6 10 _____ 7 6 _____ 8 11 _____ 9 10 _____ 10 11 _____ 11 8 _____ 12 10 _____ _____ _________ TOTAL 100 _____ 1-1. ( 2 points for either answer) Are you interested in being an undergraduate TA for this course next year? ( YES, NO ) Either answer accepted Your code: KEY Page 2 of 12 2-1. A student doing an independent project (Zoo 4905) monitored Daphnia growth in a lake, and based on their performance was able to describe how the per capita growth rate varied as a function of density. Her data are shown below. 0.4 0.2 0 dN/Ndt-0.2 0 2 4 6 8 10 12 14 (per week) -0.4 Per Capita GrowDaphnia Density (no. / 10 ml) a) (4 points) Given enough time, to what density will the population converge if initiated at the following densities: Final Density N 0= 1 0 N 0= 3 11 N = 7 11 0 N 0= 14 11 b) (2 points) Give a biologically plausible explanation for this hump-shaped function (your answer must be sufficiently complete to explain both the rise and fall of the curve). • Initial increase: Allee affect due to Type II functional response (e.g., due to handling time) or social facilitation of reproduction or feeding. • Eventual decrease: Intraspecific competition, aggregation by predator, increased incidence of disease Your code: K EY Page 3 of 12 3-1. (2 points) Dr. I.M. Green monitored a plant population’s density through time (note the logarithmic scale): 1000 100 Den10ty 1 01 234567 89 01 time (years) Over which time period does the plant population exhibit the greatest per capita growth rate (circle the correct option)? i. 0-3 yrs ii. 3-6 yrs iii. 7-10 yrs iv. The answer can’t be obtained from the data available 3-2. The dynamics of three species can be described using the following equations (where N is density, in no./m 2): dN 1N d1 = +1.0 – 0.1N – 1.1N 2 dN 2/N 2t = +0.6 – 0.2N –10.2N – 021N 3 dN 3N d3 = –0.1 + 0.1N 2 For each of the following, choose (i.e., circle) the best option from the those available within parentheses: a) (1 point) Species 1 and 2 are: ( competitors; predator and prey; mutualists, do not interact directly ) b) (1 point) Species 1 and 3: ( competitors; predator and prey; mutualists, do not interact directly ) c) (4 points) In the absence of Species 3, Species 1 and 2 will: ( both persist; only species 1 will persist; only species 2 will persist; neither will persist; there is not enough information provided ) hint: for c) apply the concept of invisibility. Your code: KEY Page 4 of 12 4-1. The following life cycle diagram is based upon a time interval of one year. 0.3 0.1 0.5 Eggs 0.6 Small 0.5 Medium 0.3 Large 0.1 Adults Juveniles Juveniles Juveniles 20 a. (3 points) What proportion of individuals in each life stage survive from one year to the next? Eggs 0.6 SJmvelliles 0.9 Adults 0.5 b. (2 points) If there were 100 individuals of each stage on April 1, 2010, how many large juveniles should there be one year later (on April 1, 2011)? LJareniles 40 = (100*0.3 + 100*0.1) c. (1 point) Given enough time (and assuming the transition values remain constant), this population will grow… (pick the best option): ( tangentially; density-dependently; exponentially; logistically ) d. (2 points) In the real-world, provide two reasons why the transitions could change (i.e., not remain constant). • Density-dependence • Change in the environment (e.g., global warming, change in predator density, invasion of a competitor, etc.) Your code: KEY Page 5 of 12 5-1. ( 3 points) You observe that a species of butterfly very common on the Florida peninsula is absent from islands in the Florida Keys. Provide three hypotheses that might explain the absence of the butterfly from the islands. • Unable to disperse across water (too far) • Abiotic environment is unsuitable • Lack of suitable host plant for oviposition by females • Lack of suitable host plant for surivival of larvae (caterpillars) • Excessive predation • Intense competition • Presence of pathogens 5-2. ( 3 points) Two species of lizards that live in oak hammocks around Gainesville. Provide at least three hypotheses that might explain how the lizards are able to coexist in hammock environments. • The don’t interact • Resource partitioning (they eat different food; occur in different microhabitats) • Disturbance (e.g., hurricanes are frequent enough to prevent competitive exclusion) • Habitat heterogeneity (related to resource partitioning) • Trade-off between colonizing ability and competitive ability. • Better competitors are more vulnerable to disturbances. • Better competitors are more vulnerable to predators (or parasites). • Neutral theory: there is no “best competitor”; instead species are equivalent and there is a slow ‘walk’ to extinction. Extinction is balanced by speciation. [this really isn’t coexistence, but we’ll give credit for this.] 5-3. ( 2 points) In class we’ve seen that increasing species richness can increase primary production. We’ve also discussed coexistence of competitors. Combine these concepts to explain why increased species richness might increase primary production. Coexistence is facilitated through resource partitioning. As a result of resource partitioning, two (or more) species will use the available resources more “effectively”: e.g., consider two plant species that partitioning nutrients – one is limited by N and one by P; their combined use of N and P (and their productivity) will be greater than either species alone. 5-4. ( 2 points) You work for the USDA and you have been charged with finding a biocontrol agent that might stem the outbreak of pine beetles. Explain at least two key traits of a biocontrol agent that you’d look for: • High attack rate (ability to find and kill prey at high rates even at low densities). • High conversion efficiency (i.e., ability to produce new predators with few prey: e.g., parasitoids). • Not harm other species • Low mortality rate. Your code: K EY Page 6 of 12 6-1. Define: a) (1 point) Exploitative competition A jointly negative interaction between two species that arises through a shared, depletable, and limiting resource. b) (1 point) Interference competition A jointly negative interaction between two species arises through direct agonistic interactions (e.g., territoriality). c) (1 point) Functional response A functional response describes the relationship between the feeding rate of a predator and the density of its prey. d) (1 point) Indirect effect An IE arises when one species affects another through its affect on the density of an intermediate species (e.g., if AÆBÆC, then A has an indirect effect on C by affecting the density of B (which in turn affects C’s dynamics). e) (1 point) Higher order interaction An HOI occurs when the density of one species affects the strength (or sign) of the interaction between two directly interacting species. 6-2. (2 points). Provide one explanation for why decomposition of soil organic matter is slow in the arctic. • Low temperature limits microbial activity • Low nitrogen availability limits microbial activity 6-3. ( 3 points). List three reasons why the marsh cordgrass, Spartina alterniflora, is considered a pioneer species in the development of eastern U.S. salt marshes. • They are highly tolerant of anoxic soils and high salinity • Their aboveground structure slows water movement, which causes sedimentation and marsh accretion • Their large root systems stabilize the substrate and prevent erosion. • Rapid clonal expansion through aggressive rhizome growth allows for the expansion of marsh areas. Your code: KEY Page 7 of 12 7-1. ( 6 points). You work for the National Marine Fisheries Service. A new species of sea life has been discovered and it makes awesome sushi. You have been charged with coming up with a management plan to ensure that this species can be harvested sustainably (i.e., it will be harvested, but you need to find a way to ensure its continued persistence and availability to fishers). You consider a range of options: • Fixed harvest (you define a fixed number of critters to be harvested) • Fixed effort (you only allow a fixed number of permits) • Spatial reserves (you restrict fishing to certain regions) Which approach (or combination of approaches) do you recommend and why (feel free to use words, equations or figures to explain your approach)? A fixed harvest approach (of which the unstable “maximum” sustained yield is a special case) is unstable. Even if a stable equilibrium is possible (at exploitation rates below MSY) the system is sensitive to uncertainty in stock size and production. Uncertainty can easily give rise to overharvesting and depletion of stocks. Fixed effort is generally better (it gives rise to a stable equilibrium) but is still problematic if uncertaintly is very large. It’s also sensitive to fisher behavior which can modify the expected harvesting-stock size relationship to generate unstable equilibria (much like with the fixed harvest scenario). Marine reserves are thought to be best because they protecet a fixed (and known) fraction of the population (at least at a given time; movement could reduce this effectiveness). As a result marine reserves are less likely to generate unstable overexploitation in the face of environmenta
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