Spiders in wheat fields and semi-desert in the Negev (Israel)

Intensively cultivated arable land and semi-desert are two dominant habitat types in the arid agroecosystem in the northwest Negev Desert (Israel). The present study compares activity-densities and species richness of spiders in these distinctive habitat types. Sixteen wheat fields and twelve locations in the semi-desert were sampled during the winter growing season of wheat. Semi-desert habitats had more spider species and higher spider activity-densities than irrigated wheat fields. The majority of spider families, namely Gnaphosidae, Thomisidae, Salticidae, Zodariidae, Philodromidae, Dysderidae, and Clubionidae had significantly higher activity-densities in the semi-desert compared to wheat. Only two families, the Linyphiidae that strongly dominated the arable spider community and Corinnidae had higher activitydensities in wheat than in semi-desert. Out of a total of 94 spider species, fourteen had significantly higher activity-densities in semi-desert than in wheat fields and eight species had significantly higher activity-densities in wheat fields than in semidesert. Spider families and species that dominated the semi-desert communities also occurred in the wheat fields but at lower activity-densities. In conclusion, the semi-desert is a potential source of spider species and families that may immigrate into arable fields during winter. In particular, active hunting spiders may be sustained in crops through immigration from nearby semi-desert habitats.