Worksheet 2-1
Ecology Lab Worksheet 2 - Field Sampling Techniques and Distribution Patterns
This worksheet is designed to help you to:
i)
Understand basic field sampling techniques.
ii)
Present collected data in a manner suitable for analysis.
Answer/address all of the following questions using complete sentences. In all cases, we require that your
work be typed and that you make computer printouts of spreadsheets and graphics.
Sampling Techniques
True species density: species A – 10, species B – 25, species C – 40, species D – 15. Compare these
numbers with your results for questions 3c and 4c, and reply question 7b.
1. State in your own words why it is necessary to conduct random sampling within a habitat (2pt).
2. What is accuracy? What is precision (2pt)?
4. Present a table summarizing the range, mean, and standard deviation of each species density estimated
from the quadrat sampling (all groups combined) (4pt). Produce a bar graph showing the mean density of
each species from the plot sampling. Include error bars and remember to label your graph (4pt). What do
you estimate the total population size of each species to be for the entire island (2pt)?
5. Perform an appropriate statistical test to determine if there is a significant difference in abundance
among the four species calculated from the plot sampling (5pt). State Ho and Ha (2pt). What is your pvalue (1pt)? Do you reject of fail to reject your null hypothesis and why (2pt)?
6. Using the transect data, present a table summarizing the mean and standard deviation of density
estimates for each species using all the groups data combined (4pt). Produce a bar graph showing the
mean density of each species from the transect sampling. Include error bars and remember to label your
graph (4pt).
7. Perform an appropriate statistical test to determine if there is a significant difference in density among
the 4 species calculated from the transect sampling (5pt). State Ho and Ha (2pt). What is your p-value
(1pt)? Do you reject of fail to reject your null hypothesis and why (2pt)?
8. Present a table comparing the density estimates of each species calculated within each of the four
groups of students from the plot sampling (mean from within their group) (4pt). Present a similar table for
the transect sampling (4pt). If you wanted to determine if estimates of density are significantly different
among the four student groups, how would you do that (2pt)? (You do not have to run the tests)
9. Given the true size of each species population, present your conclusion and discuss the findings of your
analysis and what they mean, include:
-What did the analysis teach you about the field methods that we used?
-What about your study do you think is important for others to know? WHY?
-Remember to discuss the precision and accuracy of each method and the sources of error/bias in your
methods. What could have been done to get more accurate results? What method would you use in the
future? (5pt)
Worksheet 2-2
Distribution Patterns
10. Name the 3 types of distribution patterns commonly seen in nature? (3pt)
11. Name and discuss 3 factors that affect population distribution patterns? (6pt)
12. What are your null and alternative hypotheses for this part of the lab? (2pt)
13. Complete the table below using your population distribution data for the epiphytes that you
sampled: (5pt)
Number of
individuals
per tree
(xi)
Observed
Frequency
(O) (fi)
(fx)
P(x)
Expected
Frequency
E
(O-E)2/E
0
1-5
6-10
11-15
16-20
21-25
26-more
∑
a) Show your calculations for (i) the mean value (4pt), (ii) the Poisson values (5pt) and (iii) the
Expected values (5pt).
b) Perform the chi-squared test on your epiphyte distribution data and state (i) the chi-squared value
(2pt) and (ii) the associated p-value (2pt).
c) Graph the observed and predicted values of your data (5pt).
d) Based on your answers to (b) and (c) above, describe the population distribution pattern of the
epiphytes (4pt).