Experimental Design and Population Dynamics in Salamanders and Squirrels, Exams of Ecology and Environment

Download Experimental Design and Population Dynamics in Salamanders and Squirrels and more Exams Ecology and Environment in PDF only on Docsity! Name: KEY Page 1 of 10 Instructions: --Write your name on all the pages --Make sure that all 10 pages are attached. --You may not use calculators or other electronic aids. The 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). --If you get hung up on a problem, skip it; return to it after you’ve answered the “easy” problems. GENERAL ECOLOGY PCB 4044 SPRING 2003 MIDTERM I PAGE POINTS POSSIBLE SCORE 2 12 _____ 3 12 _____ 4 11 _____ 5 12 _____ 6 10 _____ 7 10 _____ 8 9 _____ 9 15 _____ 10 9 _____ _____ _________ TOTAL 100 _____ Name: KEY Page 2 of 10 1. A species of salamander (Salamandrous imaginarius) occurs on mountains only at elevations below 2,000 m. A second species of salamander (S. secondarius) rarely co-occurs with S. imaginarius but is frequent at sites >2,000 m elevation. A species of predatory snake (Serpentes caudatovore) also is restricted to elevations >2,000 m. a) (6 points) Develop three separate hypotheses that could explain the observed distribution of one of the three species (i.e., focus on either the snake or one of the salamanders). Each hypothesis should emphasize a different process. A variety of approaches could be taken. Here’s one option focusing on the first salamander species. The distribution of S. imaginarius might be explained by one (or more) of three very general hypothesis. 1) S. imaginarius is absent from higher elevations because it is competitively excluded by S. secondarius; 2) S. imaginarius is absent from higher elevations because of predation by Serpentes caudatovore. 3) S. imaginarius is absent from higher elevations because abiotic factors: e.g., the physiological tolerances of S imaginarius may be such that they can not live at elevations greater than 2,000 m due to the low temperatures. Note that there are many more possibilities and that these three hypotheses might work in combination to limit the distributions of this species. b) (6 points) Design an experiment to distinguish among the three competing hypotheses. Include all relevant information, including details about the key components of a well designed experiment. Also be sure to mention what you will measure and what you should “see” if the different hypotheses are correct (and what you should see if it is incorrect). A number of different answers are possible (depending on the answer to part a). Here’s one possibility. Conduct an experiment using large enclosures/exclosures. Replicate each treatment (e.g., 3 reps/treatment) and randomly assign treatments to cages (within an elevation). Treatments: 1) predators (S. caudatovore) excluded but competitors present at ambient density, >2000m; 2) competitors (S. secondarius) excluded but predators present at ambient density, >2000m; 3) predators and competitors present at ambient densities >2000m; 4) predators and competitors absent, >2000m; 5) predators and competitors absent, <2000m. Introduce the target species (S.i.) into the cages, followed by their predators and/or competitors. Measure population densities over a 5 year period. Compare density in ttts 2 and 3 to test Hyp. 1 (if limited by competitors, then they should increase in density in ttt2, but not ttt3). Compare ttts 1 and 3 to test Hyp 2. If limited by predators then density should increase in ttt1 but not ttt3. Ttt 4 in combination with ttts 1, 2, and 3 can be used to infer whether competition and predation interact. Compare ttt4 and ttt5 to discern if even in the absence of predation and competion, the target can make it (negative growth in ttt5, but not ttt4 implicates factors other than competition and predation). Ttt 5 also serves as a handling control. If these animals don’t make it, then failure to establish in ttts1-4 would be discounted. Name: KEY Page 5 of 10 5. Density dependence and regulation a) (4 points) What do we mean when we say that a rate is density-dependent? Be as specific as possible (you may use a figure if it would help; and explain what kind of rates we would apply this statement to). We mean that the rate increases or decreases as density increases (i.e., that is does not stay constant). In most cases, we are concerned with per capita rates (e.g., per capita birth or death, or per capita growth rates, dN/Ndt). b) (4 points) Does density-dependence always lead to population regulation? Why or why not? Give an example (referring to a particular biological phenomenon). NO. Only certain forms of density dependence will lead to regulation. Per capita growth rates must decrease (not increase) with density to lead to regulation. For example, if food intake decreases with density and this causes a reduction in birth rates (or an increase in death rates) then regulation can result. If on the other hand, food intake increases with density (e.g., because foragers cooperate to find food and thus food finding increases with density), then the resulting density- dependence will tend to destabilize dynamics. 6. Dr. I.M. Green followed a cohort of plants through time, and at each point in time, recorded the number of survivors. The resulting data are given below (note the logarithmic scale). 1 10 100 0 1 2 3 4 5 6 7 8 9 10 age (or time) N um be r s til l a liv e (4 points) Compare the probability of surviving to the next time (or age) for young (age 0 or 1) and old (age 8 or 9) plants. Which of the following statements is correct? i. Young plants survive better ii. Old plants survive better iii. Young and old plants survive with the same probability iv. The answer can’t be obtained from the data available Name: KEY Page 6 of 10 7. Disneyworld wants to set up a new exhibit for a rare fish, the red-eyed grouper-grunt. Disney wants to have 10 adult fish for their exhibit, and have proposed several options in which they collect fish from the wild and permanently house them at Disneyworld: i) collect 50 recently settled grouper-grunts (i.e., settlers) from the wild and raise them to adulthood. They expect ~40 of these to die under lab conditions before reaching maturity (yielding 10 adults). ii) collect 20 juveniles (only half of which are expected to die before adulthood in the lab). iii) collect 10 small adults (these are adults, so there’s no “loss” raising them to adulthood) iv) collect 10 large adults Each option involves removing fish from the wild population and will thus have an effect on the long-term viability of the wild stock. As the state biologist, you have been asked to decide which option will have the smallest effect on the population growth of the wild group-grunt population. You have the following information available (assume it is accurate and that you have no other information): Stage, x Fecundity Reproductive Value 1 (settlers) 0 1 2 (juveniles) 0 2 3 (small adults) 10 4 4 (large adults) 50 2 Based on this information and your knowledge of demographic theory, what stage should Disneyworld collect (to have the smallest effect on future population growth)? a) (4 points) Circle the correct answer: 1. 50 settlers 2. 20 juveniles 3. 10 small adults 4. 10 large adults this is the best answer b) (6 points) Justify your answer using your knowledge of demographic theory: Reproductive value is the contribution an individual makes to future population growth. Our goal is to minimize the deleterious effect on population growth, which means that we want to minimize the total RV of the removed animals. 10 large animals have a combined RV of 20 (all other options are greater: 40 or 50). Name: KEY Page 7 of 10 8. A student was doing an independent project (Zoo 4905) examining population growth and density-dependence in Daphnia. She grew Daphnia in flasks, and described the relationships between per capita birth and death rates and density: 0 0.1 0.2 0.3 0.4 0.5 0.6 0 20 40 60 80 100 Daphnia Density, N Pe r C ap ita R at e (p er w ee k) birth death a) (4 points) List the equilibria (i.e., give the densities at which the equilibria occur -- ignore the “trivial” one at N=0), and indicate whether each equilibrium is stable or unstable. If it’s stable, indicate whether it is locally or globally stable. Equilibrium Density Stable or Unstable? Local or Global? 20 unstable not applicable 80 stable locally stable b) (6 points) Based on her data and using the figure below, draw out the trajectories for populations that begin at three different initial densities (N=10, N=40, and N=90). 0 20 40 60 80 100 Time Po pu la tio n de ns ity , N NOTE: other options were possible, given that time lags could result b/c Daphnia is age-structured.