Field-scale effects of farming practices on linyphiid spider populations in grass and cereals

Linyphiid spiders were sampled in three grass and four cereal fields, between October 1989-October 1990, and from one grass and one cereal field, from June-August 1991. Population growth and decline were characteristic of field type and pattern of management. Agricultural operations caused large population depletions: insecticide applications, cutting grass for silage and autumn cultivations reduced spider populations by 56% to 96%; heavy grazing caused virtual extinction. Aerial dispersal activity, monitored by water traps, showed high dispersal frequency with highest intensity in June, July and August. The results are discussed with reference to the large-scale spatial structure of linyphiid spider populations and the use of spatially dynamic models to predict metapopulation size as a function of patterns of crop management, land-use and landscape structure.