Efeitos de um gradiente térmico sobre comunidades de macroinvertebrados em riachos geotermais tropicais

Abstract

The warming causes multifaceted impacts on aquatic biodiversity, especially in tropical ecosystems. We investigated the responses of macroinvertebrate communities in tropical geothermal streams to natural temperature increases, focusing on compositional, trophic, and evolutionary components to understand the effect of thermal variation. In the first chapter, we analyzed the stability of size spectra and biomass distribution, as well as changes in the trophic levels of several species. Despite increased metabolic demands, biomass and body size structure were maintained, demonstrating trophic plasticity by species that adjust their feeding habits by consuming at lower trophic levels where biomass is more abundant. This trophic flexibility acted as a compensatory mechanism to meet the higher energy demands imposed by warming and was identified as a key factor for ecosystem resistance and functional maintenance under warming. In the second chapter, we explored taxonomic and phylogenetic diversity patterns of macroinvertebrate assemblages, assessing the effects of the thermal gradient on the phylogenetic structure of communities. Using relatedness metrics such as the Net Relatedness Index (NRI) and Nearest Taxon Index (NTI), we identified sensitive patterns of phylogenetic clustering related to thermal variation, resulting from niche conservatism. This clustering in a few streams suggests environmental filtering selecting lineages adapted to high temperatures, which restricts taxonomic and phylogenetic diversity in certain locations. However, along the thermal gradient, no systematic changes in alpha and beta diversity were detected, indicating that multiple environmental factors beyond temperature influence community assembly. These results highlight the complexity of ecological and evolutionary processes shaping biodiversity in tropical environments exposed to climate change, contributing to an integrated understanding of aquatic community resistance and vulnerability to environmental stress. Therefore, this study reinforces the complexity of warming effects on macroinvertebrate communities, evidencing nonlinear patterns and multifaceted responses. Although temperature increases impose high metabolic demands, community responses do not translate into linear declines in biomass or diversity, but rather into behavioral and structural adjustments such as trophic plasticity and shifts in trophic levels to compensate for energetic variations. Moreover, the thermal impact acts as a selective environmental filter, shaping the phylogenetic structure of assemblages and promoting uneven clustering that reflects local ecological heterogeneity and the spatiotemporal variability of habitats. These findings emphasize that aquatic communities respond to warming in a complex and nonlinear manner, resulting in responses that challenge simplistic predictions and point to the need for integrative approaches to understand and conserve biodiversity under climate change.