Goals

  1. Understanding how primate sign density can be estimated
  2. Convert sign density to animal density

1. Transect survey

Close your eyes and imagine you are in a tropical forest in Central Africa. Your mission consists in measuring the density of chimpanzees (Pan troglodytes troglodytes) in the area. You decide to count chimpanzee nests along 10 parallel transects. You walk along each transect and measure the perpendicular distance between each nest found on your left or on your right and the transect line.

Each transects measures 4km. The perpendicular distances between the transect and the nests are recorded in meters. The width of the area where signs can be detected is 50m (25 meters on each side).

The animation below illustrates the data collection:

The data you collected are available on Canvas. Open the csv file in Excel. Using the instructions available here, create a histogram using a bin width of 5m. To set bin width, right click on the histogram bars and “Format data series”.

Do not spend more than 5 minutes trying to create this histogram. Excel is not ideal for this kind of task anyway. Here is what you should obtain (approximately):

2. Sign density

Using the above histogram, estimate the number of signs (detected or not detected) that are in the \(50m \times 4km \times 10\;transects\) area that you surveyed.

Try for at least 15 minutes.

If you’re still stuck after 15 minutes, follow this step-by-step instructions:

  1. How many signs were detected in total?
  2. How many signs were detected within 5m? Why do the bars of the histogram get lower as you move farther from the transect?
  3. Assuming you did not miss any nest that was less than 5 meter away from the transect, how many nests did you likely miss in the 5-10m zone?
  4. If you had detected all the nests, the bars of the histogram would all have had the same height (height=52). How many nests would you then have detected between 0 and 25m away from the transect line?
  5. The overall area surveyed covers a surface area of \(50m \times 4km \times 10\; transects\). Estimate the number of nests per \(km^2\).

3. Chimpanzee density

A weaned chimpanzee builds a new nest every night. Infants sleep in their mother’s nest.

In the forest that you just surveyed, a previous study has revealed that nests persist in the environment for about 100 days on average.

What is the chimpanzee density in this forest ( number of chimpanzee per \(km^2\))?