Macrophyte Structural Complexity Influences Spider Assemblage Attributes in Wetlands

Macrophytes increase structural complexity in aquatic ecosystems and their emergent structures provide habitats for spiders. We sampled spiders in three species of macrophytes (Eichhornia azurea, Eichhornia crassipes and Limnobium laevigatum) and measured five traits indicative of structural complexity: horizontal structure, vertical structure, plant height, macrophyte richness and macrophyte biomass. We tested the hypothesis that spider density and diversity increase and guild composition changes along a gradient of structural complexity provided by macrophytes. Vertical and horizontal structure and macrophyte richness covaried with the attributes of spider assemblages. However, vertical structure was an important habitat-complexity trait because it covaried with all spider attributes investigated, positively affecting density and taxa richness and changing guild composition. Our findings suggest that the increase in macrophyte structural complexity, primarily through vertical structure, provides additional habitat and microhabitat variability. These forms of variability may increase the availability of prey and shelter and even reduce intraguild predation between spiders, thereby potentially increasing density and taxa richness. Moreover, an increase in vertical complexity provides available structures for web attachment, favoring web-building spiders and consequently affecting guild composition. Thus, habitat structure plays an important role in structuring spider assemblages and specific traits may mediate changes in particular attributes of spider assemblages.