Variação na abundância da araneofauna na serapilheira do chão e de bases de palmeiras attalea attaleoides (barb.rodr.)Entre o dia e a noite: o papel de palmeiras como refúgio em uma floresta da Amazônia Central

Abstract

The heterogeneity within habitat is an important factor on arthropod soil fauna in tropical forests, however, the studies about this fauna generally do not take into account the importance of structures that contribute to this heterogeneity. Palms with underground stem of the species Attalea attaleoides, due to the disposition of its leaves, accumulate leaves that fall from the canopy, which become an important refuge to arthropods. We compared the abundance and composition of spider fauna in three microhabitats: Upper leaf mound of the palm(UPLP), Under leaf mound of the palm (UNLP) and Ground leaf litter (GLL) in diurnal and nocturnal collects to evaluate the importance of the litter mound of palms to the more abundant spiders families. This study was conducted at the Experimental Farm of the "Universidade Federal do Amazonas", between June and December (season dry) of 2004. Each of the 80 sample units consisted of the leaf litter of the palm base, divided in upper and under litter, and 1 m2 of leaf litter adjacent to the palm. The spiders were hand sorted from the litter within few hours after the material was collected. We have found: 1) a strong similarity between the spiders community of the Infraorder Araneomorphae in our study area with the fauna of communities studied in other studies of litter spiders in Neotropical forests. The same was not observed within the Infraorder Mygalomorphae, possibly because they may be using underground burrows, and the studies had differences in the soil depht collected for analysis; 2) The fauna composition was similar among microhabitats, but the predominant families in the palm bases were different from the GLL; 3) There was a significant relationship between spiders abundance and litter volume in the litter from the leaf litter mound of the palms, but the same was not observed in the GLL; in this microhabitat this relationship was found only in the Infraorder Mygalomorphae; 4) Few families had differences in abundance according to type of soil; 5) There was larger capture of spiders during the day (1243) than during the night (879), however, there were families that were more captured at night and the capture rates changed according to microhabitat. Our results indicate that 1) The families composition of the Infraorder Araneomorphae representative of region can be obtained in a small area (as in our study area); comparatives studies among areas inside and outside Amazon would be of interest for the growth of the understanding of the biogeography of this Infraorder. 2) The accumulation of leaf litter affects the spiders community; several families were more abundant in the palm bases than in the GLL, however, the families composition was very similar. Probably, this higher abundance is caused by the large availability of refuges and prey (mainly decomposers). However, absence of relationship between Araneomorphae spiders abundance and volume litter in the microhabitat GLL indicates that the same do not occurs there with the spider group. 3) The more abundant families of spiders which spin webs had larger density in the GLL and in the UPLP, because of the larger availability of structures to fix their webs than in the UNLP. 4) There was weak evidence and only for two families (Salticidae and Ctenidae) that the palm mound could be a local of refuge during part of the day while the GLL would be a foraging place during the other part of the day. Apparently, the spiders of the majority families do not realize this daily movements, they do not have a different place for refuge and to capture their prey. 5) However, the variation in the abundance of spiders of a few families (Mygalomorphae, Oonopidae and Symphytognathidae) between day and night, indicates that these families are actives in litter at night and may be moving down in soil at night. 6) The larger abundance of spiders in leaf litter mounds of palm are important elements to the community of spiders in forests. However, Its importance must change according to spider family.