Guild structure, diversity and relative abundance of spiders in selected non-rice habitats and irrigated rice fields in San Juan, Batangas, Philippines

A total of 11,968 individuals were collected, of which 75% were spiderlings. These entire collections were classified into 71 species, 50 genera, 16 families, and 2 functional guilds, namely, the web spinners and the hunters. Although the vegetational structure of each habitat was different from each other, the two functional guilds were both present in all four habitats. There were significantly (p0.05) more web spinners (7722 individuals; 64.5% of the total) than the hunters (4246 individuals; 35.5% of total). The two equally most dominant families were web spinners- Linyphiidae (23.57% of total) and Theridiidae (23.56% of total), whereas, Lycosidae were their equivalent in the hunter's guild. While the Linyphiidae and Theridiidae dominated all non-rice habitats, Tetragnathidae were most preponderant in irrigated rice fields. Overall, the relative abundance of the 16 spider families varied from habitat to habitat. The species rank abundance curves were all linear in the four habitats demonstrating dominance of the rare species (1% abundance). Based on Shannon-Weiner index (H'), the spider faunal diversity was highest in the irrigated rice field (H' S. spontaneum = Malachra spp. (5 species each) P. conjugatum (4 species). Taxonomic similarity in all three non-rice habitats was high and broadly similar to each other (0.64-0.93) but significantly different from the irrigated rice fields (0.14-0.50). Species evenness (E5), however, was moderately less uniform in irrigated rice fields (0.63 + 0.08) than three selected non-rice habitats (0.68 +- 0.02). The high population density of rice-dwelling spiders, namely, Atypena formosana (Oi) and Pardosa pseudoannulata (Boesenberg and Strand) in Malachra and P. conjugatum Berg. fields after crop harvest confirmed the hypothesis that rice spiders used surrounding areas as refuge. Moreover, two non-rice habitat spiders, Harmochirus brachiatus (Thorell) and Hippasa holmerae Thorell, frequently moved to rice fields to prey on insect pests. These four species are strongly recommended for manipulation experiments to enhance biological control