Example Application of RDF-Functions: Badger Setts

In this section I will present two applications of RDF-Functions. They shall illustrate their potential use.

The examples presented here were done using the locations of six main badger setts in the area of the Knonaueramt (Switzerland) from a study conducted by Emmanuel Do Linh San (Do Linh San, 1997). In order to illustrate the use of RDFs the meadows were taken as object of concern. As shown by different authors (e.g., Kruuk, 1987), badgers often feed on earthworms found in meadows. Hence a RDF-area plot (figure 7.8) and the corresponding cumulative RDF-area plot (figure 7.9) were created for the six main setts in the area.

In figure 7.8 one can see that up to a distance of about 400m around the sett all of them except sett number 5 have comparable amounts of meadows in their vicinity. Sett number 5 has less areas with meadows within these distances, but at larger distances there is no difference compared to the other setts. A different picture is shown for sett number 4. It has a clear local minimum at distances around 1100 meters from the sett. The variation among the setts in general becomes greater at larger distances.

In this RDF plot it can be easily understood why choosing a reasonable diameter for evaluating habitat characteristics is so difficult. For each of the distances that might be used (e.g. 200m, 400m, 600m, 800m), the amount of meadows around each of the setts changes so much (200 percent and more) that completely different results can be expected in further statistical analysis steps. This situation is prevalent in many situations, but is normally neglected.

Figure 7.8: RDF for the main badger setts in the Knonaueramt area (Switzerland: amount of meadows (area in m²) with respect to the distance from the sett.

The total amount (cumulative RDF area plot) of meadows around each badger sett is shown in figure 7.9. Here we see that sett no.4 has comparable total amounts of meadows up to a distance of about 700m. After that distance only a small increase can be seen until 1300m from the sett. The total amount at a distance of 2000 meters is less than half of what is available to setts no.1 and 6.

Figure 7.9: Cumulative RDF for the main badger setts in the Knonaueramt area: cumulative area of meadows in respect to the distance from the sett.

Such findings can be used to either make predictions about the expected behavior of the badgers inhabiting these setts or helping to explain behavioral differences found in a study.