The impact of different agricultural land-uses on epigeal spider diversity in Scotland

Detailed knowledge of the biodiversity of spider communities on agricultural land is important both in terms of enhancing pest control and understanding the driving forces influencing nature conservation value. Pitfall traps were used to assess spider species diversity at 71 Scottish agricultural sites between May and September during 1996 and 1997. Land-use varied from intensive arable fields, grasslands and extensive heather (Calluna vulgaris) moorland. Spider species richness (S) was found to decrease significantly as farm management intensity increased. Several linear regression models based on the 1996 data (50 sites) and a selection of plant, soil and landscape variables explained up to 88% of the variation in species richness. Four of these models were used to estimate 1997 species richness (36 sites: 15 repeat and 21 new) and up to 58% of sites were correctly predicted to within +/- four species of the actual number caught. As only 60% of the repeat 1997 sites had values of S within four units of their 1996 score, this suggested a relatively high level of model accuracy. Model accuracy increased to 64% when all four models were used for each site, suggesting the individual models should be targeted at specific land-use types. We discuss the relevance of these models for predicting the consequences of changes in agricultural land-use for spider diversity.