Spring 2001
Practice Problems--Unit 1
Ecological tools (back to menu)
1. What is a model and why are they used? What good is a model if it isn't right?
2. Ecologists use both experimental and descriptive data to answer ecological questions. What are the pros and cons of each kind of data? When should an ecologist would collect experimental data? Why? What are situations in which an ecologist would use descriptive data? Why?
3. What are the pros and cons of doing experiments in an artificial environment? What about in a natural environment ("the field")?
4. Define hypothesis and prediction. How are they different?
5. While walking around north Tacoma, you notice that slugs chow down on some weedy plants but don't touch others growing nearby.
a. Propose one hypothesis for the ecological reason or mechanism for this pattern.b. Propose one hypothesis for the evolutionary reason or mechanism for this pattern.
c. Design an experiment to test each of the hypotheses you have proposed above. Include in each of your designs:
1. a comparison of treatments (you needn't worry about number of samples, etc.),2. an "if, then" statement of the hypothesis and predictions, and
3. what outcome would falsify your hypothesis
Evolution (back to menu)
1. What are the three necessary components for evolution by natural selection, and why is each important to the process?
2. How can we tell whether there is a genetic component to variation in a trait?
3. We mentioned the peppered moth example of directional selection in class. What are three (or more) assumptions that underlie this explanation of the change in abundance of the two forms?
4. We've talked about fish and dolphins having very similar body form as an example of convergence. Why could we not also use similar body form in fish and sharks as an example of convergence?
5. In many cases, ecologists compare the actual performance of an organism with its theoretically optimal performance (we looked at the example of clutch size in birds). What are four possible reasons that the actual performance does not reach the theoretical optimum?
Population
Ecology
Species' Distributions (back
to menu)
1. What kinds of factors can limit the distribution of a species?
2. How can you test to see whether a species' range is limited by dispersal ability? How is this test carried out? What precautions must you take in your experiment?
3. The range of sea anemone A extends no further north than northern California. The range of sea anemone B extends no further south than about the same area of northern California. How would you test the following hypotheses that propose to explain these ranges?
a. dispersal (include any precautions you would take)b. temperature limits
c. some resource limitation (you can pick one)
4. What is a species' niche?
5. How is a fundamental niche different from a realized niche? What causes the two to be different?
Climate (back to menu)
1. Why is the climate warmer at the equator than at the poles?
2. What would be the effect on global wind patterns if the earth rotated in the opposite direction?
3. At Calcutta, India (22o N latitude), there is one rainy season and one dry season each year. At Entebbe, Uganda (in Africa at about the equator), there are two rainy seasons and two dry seasons each year. Why? At what season (spring, summer, fall, winter) and what months (approximately) would you predict the rain in Calcutta?
4. Why are there deserts east of the mountains in Argentina at 35o S, but west of the mountains in Chile at 25o S?
5. a. The following climate diagram would likely represent which of the latitudes below?
J F M A M J J A S O N Da. 45o N b. 37o N c. 0o d. 37o S e. 45o S
b. Which biome would likely be found at this site?
6. What are the key features of western Washington climate? What are the causes of those climatic features? What biome characterizes the native vegetation of western Washington? How do those climatic features lead to the vegetation biome we see?
7. Your great uncle died and left you a fortune that, because of your generous nature, you have decided to use to fund student ecological research. A student's research proposal comes in hypothesizing that the distribution of a soil-growing moss species in the Puget Sound area is controlled by soil moisture. The proposal outlines a soil moisture-sampling regime that is to be carried out in western Washington in December-January (because the student is on winter break then). What comments might you make about that component of the sampling regime, and would you fund the research?
8. Why is space often thought of as a resource for barnacles or anemones but not thought of as a resource for plants?
Sampling designs (Lab 1) (back to menu)
1.Quadrat sampling: You want to design a sampling scheme to look at differences among sea anemone populations in several horizontal intertidal zones on the outer coast of Washington. You have decided on 10 circular quadrats of 25 cm radius within each zone. You have plenty of room horizontally, but you have only about 3 m of vertical distance within each zone over which to arrange your samples. Describe how you would use a random number table to locate your sets of 10 samples within each zone.
2. Mark-recapture sampling: You are interested in estimating the population of snails in your garden. Because snails don't move in and out of your garden very quickly, and because snails are easily marked with nail polish on the shell, you decide to use a mark-recapture technique, despite having to release the captured snails back into your garden. You decide to capture snails by placing a wooden plank on the soil overnight and collect the snails underneath the next day. The data are as follows: in your first sample, you capture 18 snails. You mark them all and release them. You wait a week, then resample. In that sample, you capture a total of 22 snails, with 5 marked individuals among them. What is your best estimate of the snail population in your garden?
3. Depletion sampling: Imagine that it is summer (warm and sunny) and you are getting a lot of grasshopper damage to your alfalfa seed crop. You think that the grasshoppers are living in either the abandoned field nearby or your orchard, and coming into the alfalfa field just to eat. So, you want to compare the populations of grasshoppers in the abandoned field and the orchard to see if spraying is necessary in either or both sites. Therefore, you sweepnet each site (4 strokes per sample) 10 times to deplete the local population. Although you did the sampling in 5 different sites in each habitat, the data are shown for only two of the sites, one in the field and one in the orchard. Estimate the population of grasshoppers in each of the two habitats from these data.
Sample
Field
Orchard
1
25
18
2
22
18
3
21
15
4
18
16
5
15
12
6
10
11
7
8
9
8
5
8
9
3
8
10
1
7
4. By what method would you estimate population size for the following organisms? In each case, explain why you chose the method you did and cite any assumptions that you might be violating if you don't design carefully.
a. starfish in a rocky bay several hundred meters wide
b. fruit flies around your compost pile
c. pitcher plants in a bog
d. deer mice in an area of forest
e. orcas in Puget Sound
5. Design a sampling scheme for estimating each of the following. Include in your designs any assumptions you must make for your estimates to be accurate.
a. the population of mosquitoes at your campsite by the river in June,b. the population of mice in a field next to your summer cottage, and
c. the percent of your "lawn" that is actually moss (or weeds, or bare ground, depending on your cultural methods).
6. To estimate the population of marmots in a subalpine meadow, you captured and marked 6 individuals. A week later, you captured 5 individuals, of which 2 were marked. What is your best estimate of population size? (For this question, and on an exam, don't worry about the small sample size correction. Just use the ratios to estimate the population size.)
7. To estimate the population of ladybugs on your porch one spring, you netted as many as possible in one sweep of an insect net, counted the ladybugs in your net and put them in a jar, then repeated that procedure another 9 times. You plotted the data with current catch on the Y-axis against cumulative previous catch on the X-axis and ran a regression through the data. The equation that you got was Y = 48 + .0711X. What is your best estimate of population size?
Statistics (back to menu)
1. You hypothesized that moisture controls the distribution of a plant species. So you grew some of the plants in dry soil and some in wet soil. What statistical hypothesis (null hypothesis) would you be testing when you ran a t-test on final plant biomass?
2. What does it mean to say P = 0.01? (Not the conclusion, just the meaning.)
3. What is the most general way to increase the power of a test?
4. For each of the following situations, suggest the appropriate statistical test (X2 goodness of fit, X2 test of independence, two sample t-test, paired t-test, Fisher's test, 2-way ANOVA, correlation, regression, or ANCOVA). Remember to consider whether you have replication, whether the causal variables are categorical, continuous, or both, and how many variables and/or groups within variables you want to compare. Note that you don't have to consider non-parametrics, since those would be used if the data don't fit the assumptions, and you have no way to know that here.
a. Do 3 species of barnacles live at different tidal heights? You measured the tidal height at 10 sites for species 1, 10 sites for species 2, and 10 sites for species 3.b. Does the number of chickadees visiting feeders depend on the kind of seeds you put in? You put out four feeders, each with different seeds, and counted the chickadees that come to each one over a four hour period.
c. Is soil depth associated with the population of columbines in mountain meadows? You counted the number of columbines and measured the soil depth at 15 different sites.
d. Do mosses live on moister sides of trees than lichens? You found 10 trees that had moss on one side and lichen on the other and measured bark moisture both where the moss was growing and where the lichen was growing.
e. Is dinoflagellate population growth influenced by light and temperature? You measured r in 10 populations grown in the dark at cool temperatures, 10 grown in the dark at warm temperatures, 10 grown in the light at cool temperatures, and 10 grown in the light at warm temperatures.
f. Does soil nitrogen increase the growth of grass more in the sun or in the shade? You measured the grass cover and soil nitrogen of 10 quadrats in the sun and 10 quadrats in the shade.
g. Do students spend longer eating in the sub if it's raining outside than if it's sunny? You timed the meals of 20 students on a rainy day and 20 students on a sunny day.
h. Does bumblebee flower color preference depend on background color? You set up 10 yellow flowers against a yellow background, 10 yellow flowers against a blue background, 10 blue flower against a blue background, and 10 blue flower against a yellow background and counted total number of bumblebee visits to each background.
i. Consider the data presented in Table 1.1 on page 4 of Krebs, 5th edition. The total fertility rate and gross national product per person are shown. What analysis would be appropriate to state a relationship between those two variables? Why?
6. Interpret the results (draw ECOLOGICAL conclusions) from each of the following tests.
a. b.
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Demography (back to menu)
1. What are examples of organisms with type I, type II, and type III survivorship curves?
2. What is the difference between a stable age distribution and a stationary age distribution?
3. How are cohort-based life tables different from static life tables? What are the assumptions inherent in each one?
4. The following survivorship information was collected by Slade and Balph (1974) on Unita ground squirrels (Spermophilus armatus). The ages at which survivorship was measured were determined by important events in the life cycle such as when the juveniles left their natal burrows. The researchers were interested not only in the form of the survivorship curve, but also the effect of density on survivorship. Therefore, after an initial 6 year observation period where density averaged 205 individuals, they experimentally reduced the density of the population to 100 individuals. Using a log10 scale on the Y-axis, plot the survivorship curves before and after the population reduction. (Note: The easiest way to do this is using a computer graphing program such as Excel. You will have to eliminate the 0.000 survivorship values before converting the Y-axis to a log scale.) What type of survivorship curves are these? How does density reduction affect survivorship?
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5. Here is a set of hypothetical life table data for a population of snails:
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a. Calculate l(x), R, G, and estimate r. What is the biological interpretation of this r?b. What is Vx for each age class?
6. Below is shown a life table for the winter annual plant Collinsia verna for 1983-1984 (Kalisz 1991).
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Life stage |
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seed |
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seedling |
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overwintering plants |
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flowering plants |
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fruiting plants |
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a. Calculate l(x), R, G, and estimate r. What does this r suggest about the population?
b. What is Vx for each age class?
Life History Theory (back to menu)
***1 & 2 not required in 2003***
1. What characteristics make a species a good invader? What tradeoffs exist among these characteristics?
2. Why are invasive pest species generally not invasive in their original habitat?
3. Life history tradeoffs:
a. Why is there typically a tradeoff between number and size of offspring?b. Under what conditions would you expect to find organisms that produced many small offspring? a few large offspring?
c. What tradeoff typically prevents organisms from producing lots of offspring year after year?
d. Under what conditions would you expect to see semelparous organisms (once- only reproducers)? iteroparous organisms (repeat reproducers)?
4. What explanation has life history theory put forward to explain senescence?
Population growth (back to menu)
1. Draw a graph of general exponential growth (N vs. time). Under what conditions would a population undergo exponential growth?
2. Population growth calculations:
a. If a population undergoing exponential growth doubles in 6.9 years, what is r for that population?b. If the world population has an r of 0.08, how long will it take for the world population to double?
c. The population of whooping cranes was 21 in 1955. In 1995, the population was 125 (data from Cannon 1996--see text reference). Given these two numbers, and making the assumption that growth in the whooping crane population has been exponential (see Krebs Figure 11.10), what is your estimate of r?
3. If you are given more than just a beginning and and ending population size, you can approach the estimation of r statistically. Again using data from Cannon (1996) shown below, what is your estimate of r? How does this estimate compare with that in part c of the previous problem? Do you see any intriguing patterns in the data aside from the calculation of r?
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4. Draw a graph of logistic growth (N vs. time). What causes growth to slow down? What is the term for the population size at which dN/dt = 0?
5. Draw a graph of the rate of population growth (dN/dt) vs. N. How does density affect the rate of population growth?
6. What might keep a species at a low population size relative to its carrying capacity in a particular habitat?