What is more important for structuring Dragonfly assemblages in Subtropical Grasslands lentic water bodies in the Pampa biome: space or vegetation?

Abstract

For more than six decades, ecologists have been investigating how biological communities are structured and the implications for conservation. The Niche and Island Biogeography theories stand out as the basis for predictions related to diversity-environmental heterogeneity and diversity-area relationships, respectively. Although positive relationships are expected, the relative roles of environmental heterogeneity (EH) and area in structuring lentic water body assemblages are unclear for dragonflies. We sought to investigate the effects of area and EH, expecting that there would be a positive influence on dragonfly species richness and abundance. We sampled dragonfly adults for three months in 12 water bodies in the Pampa biome of Rio Grande do Sul, Brazil. We quantified water body area and vegetation, as an EH measure to evaluate how these predictors explained dragonfly species richness and abundance. We found that water body area, but not EH, was relevant to dragonfly diversity. This indicates that dragonflies may have perceived the vegetation as homogeneous and thus moved across the landscape without perceiving barriers that would hinder new habitat colonization. Therefore, the structure of water body dragonfly assemblages in Pampas grasslands was more influenced by water body area than environmental heterogeneity. Implication for insect conservation We highlight the relevance of tropical lentic water bodies in harboring species not registered yet, an important knowledge shortfall for biodiversity. We also found a high dragonfly diversity in large water bodies, which means that in managed landscapes the conservation of large areas is required to sustain this high diversity.