Evaluating the influence of landscape, local habitat, and spatial distance on the structure of stream fish assemblages in two basins within the Western Amazon

Streams are essential aquatic ecosystems in the Amazon. The ichthyofauna inhabiting these environments benefits from the available conditions and resources, which act as environmental filters shaping species composition. This study aims to investigate the influence of landscape, local habitat, and spatial distance on the structure of fish communities in streams in the Western Amazon. Research was conducted in the Chico Mendes and Cazumbá-Iracema Extractive Reserves, located in the southwestern part of the State of Acre. A total of 25 streams were sampled, with 15 in the Chico Mendes Extractive Reserve and 10 in the Cazumbá-Iracema Extractive Reserve. To evaluate the effects of landscape variables, local habitat, and space on species richness, we used Generalized Linear Models. To assess the influence of predictor variables on species composition, we utilized Redundancy Analysis. In total, 101species were collected across the two reserves, with 49species in the Chico Mendes Extractive Reserve and 79species in the Cazumbá-Iracema Extractive Reserve. Species richness was influenced by the percentage of forest cover, which varied between reserves, while species composition was shaped by physical habitat variables. These results indicate that environmental variables at different spatial scales are crucial for the structuring of fish assemblages in Amazonian streams. Maintaining the integrity of these environments is essential for preserving habitat characteristics, which in turn support the conservation of these assemblages within and between watersheds.