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Aim To assess the exposure of 10 spider species to two drivers of global change (climate and land use), the suitability of the current network of protected areas with respect to this exposure, and the implications for a national conservation programme. Location The western Palearctic and France. Methods We predicted the current and future potential distributions of 10 spider species using species distribution models (SDMs). We explicitly quantified uncertainties in the models and estimated the future environmental suitability with discounted uncertainty. We analysed the predicted future suitability for protected versus unprotected occurrence cells. Results In this first forecast of the future of multiple spider species in the face of environmental changes, we showed that environmental changes could be confidently predicted to have serious impacts on all the studied species, with significant range contractions and expansions within a relatively short time-scale (up to 2050). We predicted that for seven of the 10 species, the current network of protected areas will conserve at least one occurrence cell in suitable conditions in the future. However, we showed that there is considerable room for improvement. Main conclusions This study illustrated how SDMs could be applied to a conservation programme for an understudied taxon such as spiders, in spite of significant uncertainties in their predictions. In addition, the uncertainties raised here compel us to emphasize the pressing need to improve our knowledge on understudied taxa such as spiders. We advocate the necessity of increasing monitoring schemes, experiments and forecasts of environmental change effects on a larger and more diversified range of species than is currently the case in the literature. [ABSTRACT FROM AUTHOR]

. 1. This study aims to develop a new method for assigning rarity weights to species in evaluations of the relative rarity of arthropod assemblages in conservation/monitoring studies. 2. A flexible characteristic was included in the rarity weighting method by introducing the possibility of fitting the method to a rarity cut-off point defined as the threshold of occurrence below which species are considered as being rare. This allows calculation of a rarity metric (index of relative rarity IRR) with multiple rarity cut-off points. 3. The proposed weighting method was used and compared with three previously proposed methods in a theoretical analysis. IRR values were then calculated for spider assemblages of a National Nature Reserve in France. Two methods of rankings were proposed: a local ranking between sites of the Nature Reserve, and a regional ranking in comparison to a reference database. 4. The proposed weighting method consistently weighted species according to the chosen rarity cut-offs. Species weights were less biased toward common species and rare species weights were less dispersed than with previous methods. Assemblages were consistently ranked according to the rarity of spiders in each assemblage. The index showed different patterns of rarity in assemblages which could not be detected by previous rarity metrics. 5. This method provides an improved understanding of assemblage rarity patterns relative to previous methods and can be consistently applied to other arthropod taxa in other geographic area and/or spatial scales. [ABSTRACT FROM AUTHOR]

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