Spatial distribution and seasonal fluctuations in abundance of spiders (Araneae) occurring on arable land at Melle (Belgium)
1993
Alderweireldt, M. (Gent Univ. (Belgium). Lab. voor Ecologie der Dieren, Zoogeografie en Natuurbehoud)
Seasonal fluctuations of spider densities are discussed as registered by means of quadrat sampling and pitfall trapping within enclosures in crop fields (especially maize and Italian ryegrass). In field centres, densities are measured of up to 66 individuals/ square meter, in field edges of up to 143 ind./ square meter. A comparison is made between crop types and between crop fields and between crop fields and other habitat types (based on a literature review). For Bathyphantes gracilis, Erigone atra, E. dentipalpis, Meioneta rurestris, Oedothorax fuscus and O. apicatus, density fluctuations are discussed in detail. Spatial distribution of spider populations was analysed by index of dispersion (Id) and patchiness values with 95 per cent limits, based on density data and on data from intensive pitfall trapping. For some species significant aggregation of the spider populations could be demonstrated in certain periods of the year (reproductive period). However, spider populations in crop fields seem to occur genrally in a 'at random' way and are less aggregated than other invertebrate groups present in the crop fields under study (e.g. Carabidae).
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