Patterns of abundance of four species of wandering spiders (Ctenidae, Ctenus) in a forest in central Amazonia

We studied spatial and temporal patterns of abundance of Ctenus amphora, C. crulsi, C. manauara and C. villasboasi, four syntopic species of medium-to -large sized wandering spiders that forage on the ground in a neotropical r ainforest. We found temporal variation, apparently seasonal, in abundance f or two of the four species. The four species are sympatric in the study are a, but with very distinct spatial patterns of abundance. Ctenus amphora was more abundant in areas with sandy soil but are also common on clay soils, C. manauara and C. crulsi are the dominant species in areas with clay soil and are infrequent in sandy soils, and C. villasboasi had a more homogenous abundance in the study area. Previous studies suggested that a predator, a rmy ants, could have an important impact on the abundance of these spiders. We estimated the frequency of attacks by army ants using pitfall traps in sandy and clay soil areas. The estimated probability of attack by army ants was higher in areas with day soil (92% per 3 months), where all species ar e frequently found, than in sandy soil areas (21%). where C. crulsi and C. manauara were almost absent. However, it is still not clear if predation by army ants is a key factor that facilitates coexistence in clay soils, and this factor can not explain the difference on the dominant species between areas with different soil types. We also discuss the description of spatial patterns of abundance as a simple, but powerful, tool seldom used for prel iminary studies on the coexistence of spiders.