Questions

1. Using the weed you've selected, design a manipulative experiment to test one of the following:

• Can your weed out-compete another important weed in your area?

• How is your weed affected by a specific predator found in your region?

Clearly state the hypothesis you are testing, and the procedures you would follow. Describe the experimental site (e.g. forest, grassland, field) or the greenhouse set-up. Give your justification for choosing field

Continued

Questions, continued.

vs. lab experiment. Give specific experimental information such as the treatments used, number of replicates and quadrat size. Make sure that your experiment is reasonable, i.e. it could be carried out within a 1-year period. What resources (people, equipment, time and money) would you need to carry out this experiment?

2. Earlier in this chapter we proposed two hypotheses to explain why a certain weed tends to be found in open habitats. Design an experiment to test the second hypothesis, that is:

• H2 - plant-eating insects that eat the weed prefer to live in shady areas, therefore only seedlings in open sunny locations survive

3. Four researchers sample a population's density by counting density in 10 1-m2 quadrats. Which researcher(s) were the most accurate, precise and least biased. The true density of the population is 50 m-2. What calculations do you need to do to make these decisions?

Researcher 1 Researcher 2 Researcher 3 Researcher 4

51

25

53

27

55

38

59

39

52

77

48

68

53

76

42

14

54

45

48

16

56

28

50

29

53

81

52

58

51

55

53

75

57

33

49

63

52

44

47

11

4. Explain why data may be precise but not accurate, or accurate but not precise. Can biased data be precise, but not accurate? Explain why.

5. Show how the values of frequency, density and cover were calculated in Fig. 10.7.

6. Complete the following life table. Construct two survivorship curves from the data: one with the y-axis on a log scale and the second with an arithmetic scale. Compare the shapes of the curves and explain why a log scale is more appropriate for displaying this type of data. On a separate graph, plot the mortality rate of the population (using arithmetic scale). Explain why it is unnecessary to plot mortality rate on a logarithmic scale. (Hint: it is a rate.)

Probability of death between age class x and x+1 (age-specific mortality rate), m=djnx

0

1000

1

100

2

50

3

20

4

12

5

7

6

3

7

2

8

0

7. Design a pre-dispersal or post-dispersal seed predation experiment, using any weed species. Make sure you ask a focused ecological question and construct an appropriate hypothesis. Is your experiment labor field-based? Explain why.

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