Space rather than vegetation heterogeneity is responsible for structuring dragonfly assemblage at lentic water bodies in Brazilian subtropical grassland

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 tropical lentic water body assemblages remain unclear, particularly for dragonflies. This knowledge shortfall is one of the factors which potentially limit biodiversity conservation. 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 cover (trees, plantations, shrubs, herbs, and aquatic plants), as an EH measure to evaluate how these predictors explained dragonfly species richness and abundance. We found that the water body area, but not EH, was relevant to dragonfly diversity. This indicates that dragonflies may perceive the vegetation as homogeneous and thus move across the landscape without barriers that would hinder new habitat colonization. Therefore, the structure of dragonfly assemblages at lentic water bodies in Pampas grasslands was more influenced by water body area than environmental heterogeneity.