Plasticidade trófica de um peixe detritívoro frente à antropização em riachos urbanos subtropicais

Abstract

The conversion of natural areas into anthropized environments is among the main causes of global biodiversity loss. This anthropogenic pressure affects small streams, whose food webs are highly dependent on allochthonous sources. Urbanization alters the availability of food resources, influencing fish and their trophic niche. In this context, the trophic structure of a detritivorous fish species was evaluated in urban streams. The stable isotope composition of δ15N and δ13C was analyzed for this bottom-feeding species across different levels of anthropization. Two hypotheses were tested: (1) the isotopic niche breadth of the detritivorous species is wider in more impacted streams; and (2) the contribution of allochthonous sources to consumer biomass is lower in streams with less natural riparian cover. The first hypothesis was partially confirmed. Consumers from stream A, the least impacted, showed the smallest isotopic niche area, supporting the initial expectation. However, this trend was not consistent across the more anthropized streams. For instance, fish from stream B, 50% anthropogenic land use, exhibited a larger niche breadth than those from stream D, 100% anthropogenic land use. The expansion of the isotopic niche reflects a less specialized diet, indicating functional instability that may compromise the trophic integrity of stream communities. The second hypothesis was rejected, as allochthonous sources particularly C3 riparian vegetation were the main contributors to consumer biomass in all streams, even in highly impacted environments. These results highlight a promising methodology that can be applied to other stream systems, reinforcing the importance of connectivity between terrestrial and aquatic ecosystems and underscoring the value of this type of approach in future research.