Deforestation around subtropical streams drives taxonomic and functional nestedness of aquatic insect communities

Abstract

Deforestation in river catchments alters freshwater ecosystem conditions, leading to biodiversity loss. However, it remains unclear whether these losses occur sequentially, resulting in taxonomic and functional nested patterns among communities. We investigated whether deforestation surrounding streams leads to taxonomic and functional nestedness of aquatic insects, reflecting differences in species tolerance to anthropogenic disturbance. We sampled aquatic insects along an environmental gradient in 100 subtropical streams with different levels of riparian vegetation loss, ranging from highly impacted to well-preserved sites. Native vegetation cover explained a significant but small fraction of the environmental variation among streams. Deforestation revealed an ordered loss of genera, with some taxa significantly associated with more forested streams, such as Macrogynoplax (Plecoptera), Hylister (Ephemeroptera) and Huleechius (Coleoptera). The reduction of native vegetation was related to a significant taxonomic (NODF = 34.56) and functional nestedness (TraitNODF = 50.96), with communities in more deforested streams forming subsets of the species and traits present in more forested streams. Mantel tests and dbRDA indicated that differences in forest cover were associated with the taxonomic nestedness component of beta diversity, but not with taxonomic turnover or with functional beta diversity components. Thus, riparian vegetation loss was mainly related to the ordered loss of aquatic insect genera in subtropical streams. Our findings highlight the importance of preserving riparian vegetation for maintaining taxonomic and functional diversity in subtropical stream ecosystems.

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