Biodiversity Monitoring Switzerland records species diversity in landscapes covering three select species groups: vascular plants, butterflies, and birds. These data have now been analyzed by Peter Pearman of the University of Lausanne and Darius Weber of the BDM Coordination Office in order to determine whether the diversities of these three species groups are connected, and if so, in what way.

The results of their analysis have been published in Biological Conservation. Pearman and Weber found that the number of plant species is connected with the number of butterfly and bird species. Species diversities of birds and butterflies, however, do not correlate: Areas populated by numerous species of breeding birds do not necessarily harbor a large number of butterfly species as well. Moreover, there is no connection to be established between redlisted species of the three species groups.

In addition, the two researchers investigated whether occurrences of common (widely distributed) and rare (scarcely distributed) species correlate with total species diversity. They discovered that it is not possible to infer an area’s overall biodiversity from the occurrence of rare bird or vascular plant species. In order to make a comparatively accurate prediction of total species diversity, roughly 90% of all species occurring in an area must be recorded, when starting with the rarest species.

Occurrences of widely distributed bird and plant species are much more indicative. If at least 25% of a region’s most common species are recorded in a sampling area, special prediction models will yield a reliable estimate of the total species number. Regarding butterflies, Pearman and Weber observed a slightly different correlation: Wherever there are many butterfly species, there are many rare butterfly species as well.

Photo: Common blue

The connection is not quite as marked in sampling areas above the timberline. For the total species number to be predicted with accuracy, more than half of all widely distributed species need to be recorded. Since above the timberline, rare species make an important contribution to species diversity, any sample needs to be large enough to be representative of scarcely distributed species as well.

This analysis shows that species diversity cannot be measured using one single species group only, as different species groups represent different aspects of biodiversity. In other words, it supports the BDM approach, which bases its recording of species diversity on various species groups.

> Complete article (in English) (with permission to publish here)

January 2008