Densitat i diversitat terminològiques dels textos del corpus del

• 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 experi-mental site (e.g. forest, grassland, field) or the greenhouse set-up. Give your justification for choosing field Continued

vs. lab experiment. Give specific experimental information such as the treatments used, number of repli-cates 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 pre-cise, 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 loga-rithmic scale. (Hint: it is a rate.)

Proportion alive at the Probability of death Age Number alive at the the start of age class x Number dying within between age class class, start of age class (survivorship) age class x to x+1 x and x+1 (age-specific x x, n_x l_x=n_x/n_o d_x=n_x–n_x+1 mortality rate), m_x=d_x/nx

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 lab-or field-based? Explain why.

Questions, continued.

General References

Brower, J.E., Zar, J.H. and von Ende, C. (1998) Field and Laboratory Methods for Ecology, 4th edn. W.C.

Brown, Dubuque, Iowa.

Gibson, D.J. (2002) Methods in Comparative Plant Population Ecology. Oxford University Press, Oxford.

Underwood, A.J. (1997) Experiments in Ecology. Cambridge University Press, Cambridge.

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