Spider (Arachnida: Araneae) on pear orchards in the "Oeste" Region of Portugal

Tese de mestrado em Ecologia e Gestão Ambiental, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2007Along six months, we studied the ground dwelling spider communities of six pear orchards, under different management agricultural practices: Conventional Agriculture (CA1 and CA2), Integrated Pest Management (IPM1 and IPM2) and Organic Agriculture (OA1 an OA2). A high number of specimens was collected and two new species were recorded to the portuguese arachnofauna. No significant differences were found in spiders diversity and abundance between the different management practices. Analysing the orchards themselves, differences were found between some of them. CA2 and IPM1 orchards had a high abundance of individuals, specially of some species, while at OA and IPM2 orchards, species abundance was more equitable. CA1 presented high diversity and abundance of spiders. We concluded that spiders react strongly to environmental characteristics of orchards. The existence of habitat diversity around the orchards, allows spider movement from the agricultural fields during pesticide applications and posterior return after it. Thus, the presence of ecological infrastructures is of major importance in the maintenance of the spider's community. We also tested the use of higher taxa surrogacy approach for spiders in this kind of agroecosystems. This approach is an effective and less expensive way to assess biodiversity. We concluded that to evaluate species' richness, genera can be used as higher taxa surrogate with reasonable accurac