Spider diversity and assemblages in different areas of the mountain forest (“selva montana”) altitudinal floor of the yungas ecoregion of Salta Province, Argentine

RUBIO GONZALO; CORRONCA JOSÉ

Sao Paulo

Congreso; 17th International Congress of Arachnology; 2007

Yungas ecoregion has a high endemism and the “mountain forest” (700-1500m.a.s.l), is one of its altitudinal floor poorly studied, and the most diverse floor of this ecoregion. Here we study the spider diversity and assemblages in different studied areas of the mountain forest and between different sites of the same area, considering two vegetational strata on each site. The samples were taken by a G-Vac during the autumn of 2006. Five samples were taken in the lower stratum (0-1mts) and 5 in higher (1-2,5mts) on each of the 8 sites of three different areas of the mountain forest of the Yungas, Salta Province, Argentina: Reserve of San Lorenzo (SL) (3 sites); El Carmen (EC) (3) and Cerro 20 de Febrero (C20F) (2). Eight hundred and seventy five spiders of 17 families (71 spp/morphospecies) were collected. Theridiidae (n=226), Pholcidae (n=188) and Linyphidae (n=123) were the most abundant families. Theridiidae (S=15), Araneidae (S=12) and Anyphaenidae (S=9) were the most diverse. Comparing the species richness and the relative abundance, the values showed EC>C20>SL; with significant differences between them (Bootstrapping method; P<0.05), in abundance and species richness only between SL-C20F and EC-C20F. The Shannon and Simpson indexes showed significant differences between SL-C20F: and SL-EC recorded more similarity in the spider assemblage (Morisita_Index=0.69). If we comparing the different sites of each studied area, we observed a significant difference in the spider abundance in EC. All the studied sites of SL were very different in relative abundance and dominance, meanwhile the sites of C20F varied only in species richness. Analyzing the assemblages similarities in the 8 studied sites of the yungas, the cluster resulted in 2 groups (SL-EC and C20F) (Bray-Curtis similarity=0.81 and 0.83, respectively), and the sites of SL were the most similar. The spider assemblage between the vegetational strata was different (Mann-Whitney-U; p=0.034), including all the calculated diversity measures; the similarity between them was moderate (Jaccard=0.45). The diversity and spider assemblage of the studied areas were different as same as the spider taxonomical composition between vegetational strata.