Biogeographical comparisons

In order to compare the species composition of one area with another, it is useful to use biogeographical comparisons. A simple measure of species richness is often inadequate as it does not inform the reader of whether there is any overlap in the species occurring at each site.

A simple technique to compare different survey areas relies only on the presence/absence of species at selected sites. The formula used is

200w/(a+b)

w = the number of shared species between the two sites
a = number of species known for the current survey site
b = number of species known from the other area

The similarity index can be used for each faunal group (i.e. birds, mammals, reptiles and frogs). The index ranges from 0 (no shared species) to 100 (identical species composition between both areas). Results can be presented in network diagrams to aid interpretation (see Woinarski et al. 1999 in your readings for an example).

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