Abstract
While many arthropod species are known to depend, directly or indirectly, on certain plant species or communities, it remains unclear to what extent vegetation shapes spider assemblages. In this study, we tested whether the activity-density, composition, and diversity of ground-dwelling spiders were driven by changes in vegetation structure. Field sampling was conducted using pitfall traps in bogs, heathlands, and grasslands of Brittany (Western France) in 2013. A total of 8576 spider individuals were identified up to the species level (for a total of 141 species), as well as all plant species in more than 300 phytosociological relevés. A generalised linear model showed that spider activity-density was negatively influenced by mean vegetation height and mean Ellenberg value for moisture. Indices of diversity (ɑ, β, and functional diversities) increased with increasing vegetation height and shrub cover. Variables driving spider composition were mean vegetation height, dwarf shrub cover, and low shrub cover (results from a redundancy analysis). Spiders, some of the most abundant arthropod predators, are thus strongly influenced by vegetation structure, including ground-dwelling species. Although later successional states are usually seen as detrimental to local biodiversity in Europe, our results suggest that allowing controlled development of the shrub layer could have a positive impact on the diversity of ground-dwelling spiders.
Highlights
Increases in plant species diversity or structural heterogeneity are often correlated with an increase in species richness of animals (Southwood et al 1979; Madden and Fox 1997)
Spider assemblages were best explained by variables reflecting vegetation structure, and vegetation closure and complexity. The importance of these variables is confirmed by the fact that we found dwarf shrub and forb cover to be positively related to ɑ-diversity and mean vegetation height to increasing β-diversity
Spider community assemblages appear to be driven by factors clearly linked to characteristics of vegetation and edaphic conditions such as vegetation height, shrub cover, pH, and soil richness
Summary
Increases in plant species diversity or structural heterogeneity are often correlated with an increase in species richness of animals (Southwood et al 1979; Madden and Fox 1997). The architectural or structural heterogeneity of plants, which is likely correlated with both plant species diversity and productivity (Lawton 1983), can be an important determinant of arthropod diversity and abundance at different trophic levels (Lawton 1983). Directly or not, on vegetation, and it shapes their assemblages (Lewinsohn et al 2005). This is especially obvious for phytophagous taxa, but has been shown for other groups using vegetation as shelter or, in the case of spiders, for building their webs. Ávila et al 2017), other studies reported a weak effect of vegetation structure on spider While strong relationships have been reported previously between webbuilding spiders and vegetation (e.g. Ávila et al 2017), other studies reported a weak effect of vegetation structure on spider
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