Characterisation of Habitat Requirements of European Fishing Spiders
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Semi-aquatic fishing spiders (Dolomedes) are dependent on wetlands, which are among the most threatened habitats, impacted by climate change and land use. There are two species of fishing spiders, Dolomedes plantarius and Dolomedes fimbriatus in Europe. Habitat loss in central Europe causes declining populations, but new suitable habitat may become available due to climate change. In order to investigate, whether new habitat might become available, I tried to characterise the habitat requirements of Dolomedes. To do so, I sampled wetland sites in Norway and Sweden. I modeled timing, placement and detectability of nursery webs to specify requirements during reproduction and to identify factors impacting detectability of the species. The results suggest differences in habitat types for both species, pointing at more narrow environmental requirements of D. plantarius, e.g. concerning dependency on open water and vegetation characteristics of the terrestrial as well as of the aquatic habitat. I found placement of nursery webs determined mainly by distance to water, shade, presence of aquatic vegetation and abundance of Phragmites, Carex and Sphagnum; detectability was impacted by cloudiness, temperature and vegetation structure; the number of nursery webs was determined mostly by the time during the season, whereby the number decreased between July and September. Further research will be necessary to refine the conclusions and to make predictions about possible range expansion of Dolomedes.