Potencial e limitações do uso do tamanho corporal como característica funcional para a bioavaliação de riachos tropicais.

Abstract

Aquatic ecosystem degradation, driven by land use changes and anthropogenic pressures, compromises biodiversity and riverine integrity. Freshwater benthic macroinvertebrates, due to their high diversity and variable tolerance to disturbances, are widely used as bioindicators of environmental quality. Body size in these organisms is a promising functional trait for assessing the effects of anthropogenic disturbances on aquatic biota. This study investigated the effects of physical habitat and environmental quality variables on the body size of immature forms of mayflies, stoneflies, caddisflies, dragonflies, and fishflies. We expected larger mean body sizes in streams with better ecological condition and differential responses to environmental variables among taxonomic groups. The study was conducted in the hydrological unit of the Furnas Reservoir, Rio Grande basin, Minas Gerais, Brazil. Forty streams were sampled along a gradient of ecological conditions. Individuals were identified to the genus level, photographed, and measured using ImageJ software. Data analyses included variable preselection, Random Forest modeling with Accumulated Local Effects (ALE) evaluation, and Generalized Additive Mixed Models (GAMM). The models indicated that variation in mean body size among the studied organisms was primarily explained by taxonomic identity and sampling site. This suggests that body size is an intrinsic trait, largely controlled by biological and phylogenetic factors, and its use as an ecological indicator should consider taxon-specific variability and local environmental context. Our results further suggest that moderate local disturbances may favor larger organisms. In taxon-specific analyses, mayflies and dragonflies responded to environmental disturbance variables, while stoneflies, caddisflies, and fishflies exhibited more stable biological patterns. We recommend that similar predictive studies incorporate refined taxonomic identification and taxon-specific predictor selection. Although body size is a promising functional metric, its application requires multifactorial and integrative approaches to properly assess the structure and health of aquatic communities.