Does the structural complexity of aquatic macrophytes explain the diversity of associated spider assemblages?

Differences in species richness and species composition of spiders associat ed with aquatic macrophytes of different structural complexities were exami ned in the Pantanal floodplain of Mato Grosso do Sul, Brazil. The plants st udied were Nymphaea amazonum (Nymphaeaceae), Salvinia auriculata (Salviniac eae), Echinodorus paniculatus (Alismataceae) and Eichhornia azurea (Pontede riaceae), whose classes of complexity were determined based on their leaf a nd branch densities, vertical structure, and height. Data were collected fr om 62 monospecific plant patches in temporary lentic environments. A total of 235 spiders of 33 species in 13 families was collected. Nymphaea amazonu m, the plant with the lowest complexity class, did not provide adequate sit es for the establishment of spiders, and only four individuals of four spid er species were found on its patches. Salvinia auriculata and E. paniculatu s shared the intermediate class of complexity, but showed statistically sig nificant differences in composition and richness of spider species. In E. p aniculatus, greater height and lower leaf and branch densities favored the establishment of web weavers, whereas the smaller height and higher density of S. auriculata promoted the occurrence of wandering spiders. Eichhornia azurea, the plant with the highest complexity class, presented the greatest number of unique spider species, differing from the other plants in spider species composition. Results indicate that richness and composition of spi der species associated with aquatic macrophytes in the study site are influ enced by the structural complexity of these plants.