The development of some elements of the arthropod fauna of a new polder.

The carabid and spider faunas of a young polder, reclaimed from a tidal flat, was studied in two areas with pitfall traps. Data are presented on the soil and the vegetation.A total of 100000 specimens of 58 carabid and 55 spider species was caught. Those catches could be compared with data from a nearby area in an older polder representing a later successional stage. The data are described with d (an index of dominance), α (the index of diversity), AV (a measure of the annual variability of population growth rates), and with dominance-diversity curves. After six years the carabid and spider faunas of the polder areas were less diverse than those outside the polder. The carabid fauna was very unstable, the spider fauna less so. This indicates that carabids reflect the changes in the habitat more clearly.Principal component analysis shows the development of the vegetation to have a major influence on the saline habitat; in carabids desalination of the soil also is important. The way in which the carabid and spider faunas developed is related to the low resource levels and high adversity and to the durational instability of the polder habitat.