Optimizing survey methods for spiders and harvestmen assemblages in an Amazonian upland forest

Abstract

Invertebrates can be sampled using any of several well-established, rapid and cost-effective methods for documenting species richness and composition. Despite their many differences, different orders of arachnids have been often sampled together in various studies. Active nocturnal search has been long considered the most efficient method for sampling spiders and harvestmen in tropical forests. We compared the number of species and composition of spiders and harvestmen simultaneously sampled using three sampling methods: beating tray, active nocturnal search and Winkler traps at areas along the Urucu River, Coari, Amazonas. We found that a reasonable inventorying of harvestmen can be accomplished solely by nocturnal search, whereas the beating tray and Winkler approaches are redundant. For spiders, both the nocturnal and beating tray methods were complementary and are needed to provide a more complete picture of spider assemblages. An inventory based solely on nocturnal search saves 75% of the survey costs for harvestmen assemblages and 46% for spider assemblages. Based on our findings we propose that different taxonomic groups (e.g. harvestmen and spiders) should be sampled separately in tropical forests, especially for monitoring purposes, and different sets of methods should be combined for each according to their most efficient and best cost-benefit performance.

Marked compositional changes in harvestmen assemblages in Amazonian forest islands induced by a mega dam

“…Those results are quite uncommon because E. aff. duapunctata followed by other species of the same genus and at least one or two species of Gagrellinae (Sclerosomatidae) are the most common, widespread and abundant species (Tourinho et al ., , ; Porto et al ., ). Additionally, Cosmetidae, Sclerosomatidae are among the top most diverse and abundant species/families in virtually all investigated sites in the Amazon (Bonaldo et al ., ; Tourinho et al ., , Porto et al ., ; Tourinho et al ., ) and our results in mainland followed this pattern as expected in undisturbed areas.…”

“…According to several other studies, the diversity of harvestmen recorded on the islands was low (Pinto‐da‐Rocha & Bonaldo, ; Bonaldo et al ., ; Tourinho et al ., ; ; Colmenares et al ., ; Porto et al ., ). The small number of species detected per island also reinforces diversity impoverishment in forest fragments, as suggested for the Atlantic Forest (Bragagnolo et al ., ) and temperate forests (Černecká et al, ; Mihál & Černecká, ).…”

“…The small number of species detected per island also reinforces diversity impoverishment in forest fragments, as suggested for the Atlantic Forest (Bragagnolo et al ., ) and temperate forests (Černecká et al, ; Mihál & Černecká, ). Indeed, more than half of the sampled islands exhibited only one to five species, whereas mainland sites retained 11–20 species, exhibiting a similar pattern obtained in other Amazonian sites (; Bonaldo et al, ; Tourinho et al ., ; ; ; Porto et al ., ). The intense sampling effort applied in this study – 20 islands (four replicates each) – is also an indicative of islands impoverishment (160 h sampling).…”

“…Between 2006 and 2008, we systematically sampled harvestmen assemblages (Fig. ) using four 300‐m 2 transects (30 m × 10 m) at each forest site, separated by 30 m, totalling 1200 m 2 of transect area per site (see Tourinho et al ., ; ; Porto et al ., ). To avoid edge effects on islands, transects were established at least 250 m from the nearest forest edge.…”

Marked compositional changes in harvestmen assemblages in Amazonian forest islands induced by a mega dam

“…duapunctata followed by other species of the same genus and at least one or two species of Gagrellinae (Sclerosomatidae) are the most common, widespread and abundant species (Tourinho et al 2014, Porto et al, 2016. Additionally, Cosmetidae, Sclerosomatidae are the top most diverse and abundant species/families in virtually all investigated sites in the Amazon (Bonaldo et al, 2009, Tourinho et al, 2018, Tourinho et al, 2014, Porto et. al., 2016 and our results in mainland followed this pattern as expected in undisturbed areas.…”