Homework 4 – SMALL MAMMALS’ HABITAT CHOICE
INTERPRET DATA AND HYPOTHESES
(To be completed in lab)
Name: ____________________________
In Lab 1 we raised the question: What determines habitat choice of small mammals? You developed
two hypotheses/predictions to answer that question. Here are two hypotheses/predictions similar to
those developed by students in Homework 2.
1) If ease of escape influences habitat choice,
then 1) shrew and vole density will be greater in plots with greater plant biomass, and
2) mice density will be independent of plant biomass.
2) If food availability/preference influences habitat choice,
then 1) shrew abundance will be greater with greater arthropod abundance,
2) vole abundance will be greater with greater plant biomass, and
3) mice abundance will be independent of arthropod abundance and plant biomass.
In Labs I and II you gathered the data necessary for today when you will interpret each prediction (were
they correct?) and decide if the data support each hypothesis.
Go to Lab I: Tables 2, 3, 4, 5. Add the estimates from the Friday AM lab and the Thursday PM lab to
yield the total estimated population size of each type of mammal in each of the two fields in 2008. Add to
Table 1 below in the row for 2008. Calculate mean values for each mammal type in each field type. Add
to the Table below.
Go to Lab I: Table 1. Calculate mean value for stem density and plant biomass. Go to Lab II: Table 1.
Calculate mean values for arthropod abundance and arthropod biomass. Add to the Table below.
TABLE 1
Mean Stem Density
Mean Plant Biomass
Mean Arthropod Abundance
Mean Arthropod Biomass
Population Sizes
Mice
2004
2005
2006
2007
2008
mean
Voles
2004
2005
2006
2007
2008
mean
Shrews 2004
2005
2006
2007
2008
mean
1 year
5 year
789
15.3
414
14.6
10
27
11
3
1
10.4
37
7
3
20
0
13.4
3
0
2
4
0
1.8
12
17
3
3
3
7.6
23
5
4
10
0
8.4
7
0
2
2
0
2.2
(from Lab 1)
(from Lab I)
(from Lab II)
(from Lab II)
(from Lab I)
(from Lab I)
(from Lab I)
INTERPRETATION OF RESULTS
Hypothesis/Prediction 1
Were the predictions correct for the habitat of choice for each type of small mammal?
1) mice ___depends on your section’s data.___________
2) voles ______________
3) shrews _____________
Given that summary of results, what do you conclude about Hypothesis 1?
Is there support for it?_______________Is the hypothesis proven? __No______________Explain.
Experimental results do not PROVE hypotheses; they support them. We never know if other unknown
factors explain the results or if, when repeated, we would get the same results.
Is plant biomass the most important variable affecting small mammal speed of movement? Maybe not.
What variable might be more appropriate to measure? __stem density________________________
Why? Mammals move mostly at ground level and have to maneuver around stems, not all of plant
biomass.
Hypothesis/Prediction 2
Were the predictions correct?
1) mice ________depends on your section’s data._____________________
2) voles _____________________________
3) shrews ___________________________
Which variable more closely predicts shrew and mice abundance: arthropod abundance or arthropod
biomass? Why? depends on your section’s data.
What is an alternate hypothesis that answers the original question?
(HINT): Recall the question: What factors (plural) determine habitat choice?
If both ease of escape and food availability determine habitat choice,
WRITE A SUMMARY
In the first paragraph of the Discussion section of a scientific manuscript, we 1) provide an overall
summary of the results and 2) state whether the hypothesis was supported.
1. Here is an example of the first paragraph of a discussion in three sentences. E.g. for
Hypothesis/Prediction 1, the text might read as follows:
“The density of both shrews and voles with low agility was greater in plots with greater plant
biomass, while the density of mice with high agility was independent of plant biomass.
These results support the hypothesis that ease of escape influences habitat choice of small
mammals. Apparently, the shrews and voles with low agility require denser vegetation to hide
from predators than do the fast moving mice.”
Note we state the correct predictions as facts; if incorrect, state that result instead. Then we state
whether or not the results support the specific hypothesis. Then we expand to explain the hypothesis
more explicitly for each type of mammal.
2. Write the second paragraph of a discussion in three sentences about Hypothesis/Prediction 2.
Depends on your sections results…
e.g. “The density of shrews was greater in plots with _______arthropod abundance, while the density
of voles was greater in plots with _______plant biomasss. Mice abundance was larger independent
of the two variables. These results (do or do not) support the hypotheseis that food availability
influences habitat choice. Apparently, multiple, not single, factors affect habitat choice of small
mammals.