Introduction to Studying Ecology
Part 1: Measuring ecological parameters and processes
Speculate on methods and procedures that could be used to address the
following questions for organisms within the Arboretum forest on KSU
campus. Be creative. Consider the difficulty of measuring the following
parameters directly.
Stand on the trail and look out 25 meters or so to each side. To which side
of the trail (up the slope or down the slope) does the production of
vegetation appear to have been greater?
What specifically would you measure to determine this and how would you go
about measuring or estimating this parameter?
How would you decide where to sample?
How could you determine how many individuals there are in the squirrel
population of the Arboretum? (Try counting them while you walk around.)
How could you determine the age that squirrels in the Arboretum most likely
to die?
How might you go about determining whether differences in vegetation are
the result of differences in the rate at which squirrels consume seeds and
nuts?
Part 2: Excel Assignment
Create the following tables and graphs and conduct the indicated statistical
analysis based on the data collected by the class in the forest behind the science
building (download data from the lab website). Use the data from your class period.
All tables and graphs that you create should be formatted according to the
expectations given in Chapter 8 of Jan Pechenik’s “A Short Guide to Writing About
Biology”.
1. Calculate the mean and standard deviation for each parameter at each of
sites we sampled (fill in table on next page).
2. Using the data from the previous table, create four bar graphs where each
bar represents each site for a single parameter (i.e. the first graph should
show the mean light intensity at each of the sites, the second should show
the mean soil temperature at shallow depth at each of the sites, etc.)
3. Conduct a t-test comparing soil temperature at shallow depth at two of the
sites (compare the “Hillside young stand upper” to the “Hillside young stand
lower” ). Then conduct a t-test comparing light intensity for these same two
sites.
4. Conduct a t-test comparing soil temperature at shallow depth at two of the
sites (compare the “Older Forest” to the “Bare slope” ), and report the
results of your t-tests. Then conduct a t-test comparing light intensity for
these same two sites.
5. Create a single scatter graph showing the relationship between soil
temperature at shallow depth and light intensity for all data points across all
sites.
6. From the data used in the graph above, calculate correlation coefficients for
the relationship between light intensity and soil temperature at shallow
depth. Use the table provided (Table 1 in the Excel Reference link to our
class lab webpage) to determine the significance of these relationships.
7. Write a brief paragraph summarizing any trends in environmental
characteristics over the area sampled. Discuss possible reasons for
similarities and differences among sites. You should include information on
the possible effects of environmental differences on organisms that might
live in any of the three sites. Support for any of your generalizations must
be based on data you have summarized in the preceding tables and/or
graphs.
Mean and standard deviation by site:
Location
Light
(lux)
Soil
Temp
shallow
(°C)
Soil
Temp
deep
(°C)
Air
Temp
(°C)
Mean
Mean
Mean
Mean
Light
(lux)
Std.
Dev.
Soil
Temp
shallow
(°C)
Std.
Dev.
Soil
Temp
deep
(°C)
Std.
Dev.
Air
Temp
(°C)
Std.
Dev.
Older
forest
Hillside
mixed age
stand
Hillside
young stand
upper
Hillside
young stand
lower
Hillside
meadow
Bare slope
P-value from t-test comparisons:
Hillside young
stand upper
vs. lower
Older forest
vs. bare slope
soil temperature
shallow
light
Place an asterik beside those P-values that are considered significant (p<0.05)
Results of correlation analysis between light and soil temperature shallow:
All data
r
P-value
Statistical Appendix
To more concisely describe a large set of samples, we often calculate measures of
central tendency, such as the mean (arithimetic average), mode, and median.
However, these only describe the overall magnitude of the parameters sampled, and
not how different the samples are from one another. Another set of descriptive
statistics are measures of variablility such as range (the maximum minus the
minimum sample value), standard deviation, and variance.
Variance =
∑(X - mean)2
n- 1
where X is the value of each individual sample, and n is the sample size.
The greater the variance, the greater the average distance of the sample values
from the mean of all sample values. Standard deviation is simply the square root of
variance.
For this lab variance can be calculate by either using the formula above, a scientific
calculator, or the Excel command for calculating standard deviation.