Tourinho, A. L. | Search bioRxiv

bioRxiv2019

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

Mega hydroelectric dams have become one of the main drivers of habitat loss in tropical forests, converting large tracts of pristine forests into isolated forest islands. Understanding how biodiversity cope with landscape modification in these archipelagic landscapes is of paramount importance to assess the environmental consequences of dam infrastructure and propose mitigation actions for biodiversity conservation. In this context, harvestmen (Opiliones, Arachnida) comprise a good indicator taxon of habitat quality, given their high sensitivity to desiccation and microclimatic change. Here, we investigate the effects of landscape change induced by a mega hydropower dam on forest harvestmen species richness, abundance and composition within the Balbina Hydroelectric Dam, Central Brazilian Amazon. Using both nocturnal search and diurnal beating tray surveys, we sampled 20 islands and five mainland continuous forests, relating our biological response variables to local, patch and landscape scale metrics. We captured 783 harvestmen representing 31 species, 22 genera and 9 families considering all sampling sites, with species composition differing across islands and mainland sites. Although species richness was unaffected by any local, patch and landscape variables, species composition and abundance were differentially affected by a set of predictor variables at different scales. Forest cover and fallen woody stems were significant predictors of species composition patterns, whereas vegetation density, forest cover, island area, abundance of palm trees, and fallen woody stems best explained harvestmen abundance. We recommend retaining large forest habitat patches surrounded by a great amount of forest cover to prevent the rapid decay in tree communities and minimize forest disturbance effects in large hydroelectric dams.

ecology↗

bioRxiv2016

Trade-offs in the use of multiple survey methods for spiders and harvestmen assemblages in an Amazonian upland forest

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.

ecology↗