Vole Population Sampling
Building on what you learned in the Tadpole Population lab you are
now assigned to sample Meadow Voles. Meadow voles are small
rodents usually found in meadows and, surprisingly, in houses
where they are often called meadow mice. You will again use mark-
recapture techniques to estimate the population size. This model
includes a few additional variables to more closely simulate a
natural population.
The model can be found here:
http://virtualbiologylab.org/NetWebHTML_FilesJan2016/MarkRecaptureModel.html
PART 1: Sampling for a Population Estimate
You will start with the default settings to familiarize yourself with the model. In this part you will set out
4 traps wherever you like in the habitat and then conduct 5 rounds of sampling to collect your data. You
will use these data to calculate a population estimate.
First place your 4 traps within your sampling plot. Use the “move trap” controls in the lower right to
position your traps wherever you think is best. Then select “Go” to start the voles moving. When you’re
ready select “Open/Close” to open your traps for the 2-hour sampling period. When the traps close,
select “Mark Voles” to mark your captured voles then select “Release Voles” to release your voles.
Record the number of voles you marked (The lower left box with yellow show total marked) and allow
the voles to move around. Then open the traps again. Complete 5 rounds of sampling and record your
data in a Data Table on the Answer Sheet. Then show your calculation for the Population Estimate.
Population Estimate = (Total Number Captured) x (Total Number Marked) by Total Number Captured with Mark
On the bottom of the simulation screen in the yellow boxes the “L-P Estimate” and “N” are given. The L-
P estimate is the calculated estimate of the population and is calculated for each sampling round. Your
population estimate is calculated using a pool of 5 sampling rounds. N is the actual population size.
1. How well does your estimate compare to the actual population size?
2. What parameters would you change, if any, to get a better estimate of the population size?
For Part 1 you must submit the Data Table, the population estimates using the equation above and showing your work, and the answers to questions 1 and 2.
PART 2: Clumped Distribution
This simulation includes a few additional variables in order to more closely simulate a natural
population. In this part you will be able to adjust the distribution of the voles to a clumped distribution.
In a natural population, animals are not always uniformly distributed and may be clumped in family
groups or to take advantages of resources.
Set the “Distribution” parameter (located under Demographics in Green) to “clumped”. You can move
the traps to new locations and then create a new population of marked voles as in Part 1. Then run
another set of 5 trapping trials to estimate the vole population. Record your data in a Data Table and
show your calculation for the Population Estimate.
3. How well does your estimate compare to the actual population size?
4. What parameters would you change, if any, to get a better estimate of the population size?
For Part 2 you must submit the Data Table, the population estimates using the equation above and
showing your work, and the answers to questions 3 and 4. (2 pts.)
PART 3: Trap Experience
The last parameter to manipulate is “Trap Experience”. Some species find trapping to be a highly
stressful (negative) experience: You are trapped in a small unfamiliar place, often crowded with other
individuals. Then you are picked up and handled as measurements are taken, and in many cases you are
even tagged (Enjoy that new earring!) Other species aren’t very stressed by the trapping experience
(positive) and don’t seem to mind being handled. All they are interested in is the bait. A free meal is
worth the handling and these species will happily go into any traps they encounter.
FOR THIS PART YOU ONLY NEED TO COMPLETE ONE OF THE FOLLOWING: A OR B.
A. If you think the trapping experience is positive, then set the Trap_Experience parameter (located
under Demographics in Green) to “positive”. Keep the distribution on “clumped”. You can move the
traps to new locations and then create a new population of marked voles as in Part 1. Then run another
set of 5 trapping trials to estimate the vole population. Record your data in a Data Table and show your
calculation for the Population Estimate.
OR
B. If you think the trapping experience is negative, then set the Trap_Experience parameter (located
under Demographics in Green) to “negative”. Keep the distribution on “clumped”. You can move the
traps to new locations and then create a new population of marked voles as in Part 1. Then run another
set of 5 trapping trials to estimate the vole population. Record your data in a Data Table and show your calculation for the Population Estimate.
5. How well does your estimate compare to the actual population size?
6. What parameters would you change, if any, to get a better estimate of the population size?
For Part 3 you must submit the Data Table, the population estimates using the equation above and
showing your work, and the answers to questions 5 and 6. (2 pts.)
PART 4: Conclusions
7. In a paragraph briefly explain how distribution and trap experience of the Meadow Vole influences
the Mark/Recapture population estimate. (2 pts.)
8. Based on the Trap Experience you chose (negative or positive) and a clumped distribution pattern
what parameters do you recommend for a successful mark/recapture protocol? (2-3 sentences) (2 pts.)
For Part 4 you must submit the answers to questions 7 and 8
