Correlations Between Distributions of Hunting Spiders (Lycosidae, Ctenidae) and Environmental Characteristics in a Dune Area

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Abstract
1. This study forms part of an extensive ecological programme caried out by staff members and students of the Department of Animal Ecology of the University of Leiden in the dune area "Meijendel", exploited as catchment area of the Dune Waterworks of The Hague. 2. This research is a follow-up of a previous study (VAN DER AART, 1973) on distribution analysis of hunting spiders by means of principal component analysis. 3. The aim of this study was to trace down the main environmental factor responsible for the distributions of the species studied. 4. The main environmental factor governing the distributions of the species in this study matched with the one found in the previous study based on material collected 10 years ago. 5. The "density of activity" curves for the different species in this study were the same as those found from the catches of these species made 10 years ago in a much wider area and with a slightly different sampling technique. 6. The numbers of the species of hunting spiders caught show a very strict, well- defined and reproducible relationship (Fig. 5) to a basic factor (principal compo- nent). This factor is called main environmental factor. 7. In order to get grip on the nature of the main environmental factor governing the distributions, twenty-six environmental characteristics were measured on twenty- eight sampling sites. 8. The environmental characteristics measured appeared to cluster in groups of mutually highly correlated environmental characteristics (Table VII). 9. No strict linear relation between the main environmental factor (principal com- ponent) and any environmental characteristic measured was found. The amount of light penetrating all vegetation layers approximates this ideal linear relation best. 10. The technique of principal component analysis was adapted to ecological distrib- ution analysis in two respects: 1. The supposed additive effect of underlying factors was transformed into a more realistic proportionate effect. 2. The supposed linear relationship between an environmental factor and its effect on a biological phenom- enon was substituted by an optimum curve.

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