The spider fauna of two intensively grazed pastures was studied by means of pitfall trap ing and quadrat sampling. Special attention was paid to the distribution of the spiders in islets of higPher grass and shortgrazed patches during day and night. An overall relationship was found between the preference for one of the two studied microhabitats and the diurnal activity: s iders active durin the night show a preference for higher vegetation (e Pachygnatha clercki, Oedotiorax upicatus) an%day active spiders prefer short vegetation (e.g. Purli?dsa-species, Erigone dentipalpis). Oedothorax fuscus and 0. retusus are shown to retire in the islets at night. Some abiotic and biotic characteristics of high and short vegetation were studied. Based on observations of certain abiotic and biotic parameters, explanations for the differences in spider fauna of the two microhabitats are postulated.From the point of nature conservation it would therefore seem to be worthwhile to try to combine both high and low vegetation in one particular habitat. Extensive grazing has been proposed as a management practice to accomplish such combination of the two structural microhabitats (MORRIS 1969). U.S. Copyright Clearance Center Code Statement: 0044-2240/89/0705-0455 $ 02.50/0 693-710. of Carabidae in agroecosystems. Pedobiologia 23, 295-303. sampling methods, and population characteristics. J. Anim. Ecol. 31, 571-599. 15-34.

No abstract

Field experiments with habitat manipulations were conducted in Belgian crop fields in order to follow changes in abundances and species composition of the spider taxocoenosis. Spider densities increased spectacularly in plots with holes (up to 13 times) in the soil. Moreover, this density increase depends on the diameter of the holes, with diameter 9.5 and 5 cm being the most effective. Species composition in the plots with holes also changed considerably compared to control plots. Exclusively web building Linyphiidae (Bathyphantes gracilis and Lepthyphantes tenuis) took far more advantage of the new possibilities offered by the habitat for web construction than non web‐building spiders. B. gracilis preferred holes with a diameter of 5 cm whereas L. tenuis was more abundant in the D9.5 cm plots. It is concluded that this kind of relatively simple habitat manipulations are advantageous for population levels of certain beneficial polyphagous predators, such as spiders. This might offer possibilities for biological control of pest populations.

The role and relative importance of polyphagous predators in maize fields has been studied from 1986 onwards. The present contribution, on Carabid beetles, assesses the seasonal density fluctuations in a maize field and its grassy fringes. Data were gathered during one year cycle by means of quadrat and fenced pitfall trapping. An attempt is made to evaluate the role of the field edges as a refuge and/or reproduction site for these predatory beetles. Reproduction, as deduced from the occurrence of an increased larval density, is not limited to the plot centre, but for some “field” species seems to take place in the boundary too. The data on some other species support the idea that field boundaries are important as hibernation refuges for ground beetles. Zusammenfassung Populationsdynamik der Laufkäfer und ihrer Larven in einem Maisfeld und im Feldrandbereich In einem einjährigen intensiven Feldversuch wurden in einem Maisfeld und im Feldrandbereich die Saisonfluktuationen der absoluten Abundanz bei Carabiden und ihren Larven mittels verschiedener Methoden untersucht. Die Fortpflanzung ist ‐ wie durch das Auftreten einer erhöhten Larvendichte abgeleitet werden konnte ‐ nicht auf das Feldzentrum beschränkt, sondern wurde für einige “Feldarten” auch im Feldrand festgestellt. Dieser Randbereich ist ein wichtiges Überwinterungsrefugium für Carabiden.

No abstract