WLF 448: Fish & Wildlife Population Ecology
Lab Notes 5, Fall 2008

Capture-Recapture

Scenario

As part of your new job as a research technician, you helped collect data on the population response of deer mice (Peromyscus maniculatus) to grazing. A pilot study was conducted in the Curlew Valley of southeastern Idaho. Mark-recapture was used to estimate the abundance of deer mice in 9 small isolated fields (3 with no grazing, 3 with moderate grazing, and 3 with high-intensity grazing). A trapping grid consisting of 70 live traps, spaced 15 m apart, and covering 0.81 ha was established in each field. Trapping was conducted for 10 consecutive nights (per field). As part of the preliminary data analysis, your boss has asked you to analyze data from one field. The raw data have been summarized in an XY-reduced file format (file peromysc.cap). Your assignment is to: (1) write a command file (i.e., input file) using 2CAPTURE, (2) analyze the data using program CAPTURE, and (3) interpret the output, i.e., answer the following questions:

1. How many individual animals were captured? (1pt)

2. How many animals were captured more than once? (1pt)

3. What percent of the animals caught on the fourth night were new captures (first time captures) (1pt)

4. What was the mean of the maximum distance (in meters) between capture points for all deer mice captured 4 times? (hint: look at the summary tables in your output, assuming you selected "Summary" in 2Capture). Why might this number increase for animals caught more frequently (i.e., explain the increase in the  mean maximum difference between 2, 3, 4, 5, and 6 captures)? (2pts)

5. Which model did you use to estimate abundance? Explain this model in your own words (assumptions of the model). (2pts)

7. What is the estimated probability of capture under the appropriate model? What is the estimated probability of recapture under the same model? What   does a higher probability of recapture imply? (3pts)

8. What is the estimated population size under the appropriate model? What is the approximate 95% confidence interval for this estimate? (2pts)

9. Do you consider this a good estimate of Peromyscus abundance in the sample you analyzed? Why or why not? (Hint: consider the precision of the estimate, robustness of the model selected, and probability of capture given N<100). (3pts)

CAPTURE input and output files. = 3pts.

Turn in the following (due next week):

• Hardcopy of your input file.

• Hardcopy of your output file(s). Note: you can call the output file into a wordprocessor, "clean up" the output, and then print the applicable portions. If you take this approach, select a small Courier font to keep numbers aligned.

• Answers to the questions. Note: please include the question or a shortened version of the question with your answer. Also, answers should be typed and double spaced.

 Problem sets are due at the beginning of lab the following week - if they are not turned in at that time, we will deduct 2 points per day up to a maximum of 1/2 the total available points. THERE WILL BE NO EXCEPTIONS TO THIS RULE!!!!!