Abstract
Due to the existence of terrestrial barriers to freshwater fish dispersion, it is believed that its distribution is strongly associated with historical factors related to the formation of the habitats they occupy. By the other hand, some studies reveal the influence of abiotic conditions (such as size of water bodies, pH, conductivity) on the composition of fish fauna occurring in small streams. This study aimed to investigate whether drainage basins, because catchment boundaries are potential barriers to fish dispersion, or the physical structure and physico-chemical characteristics of water have a greater influence on fish community structure in small streams. We sampled 22 streams belonging to five drainage basins in the Madeira-Purus interfluve. Fish were caught with dip nets and a small trawl, and data were simultaneously obtained on structural characteristics of the streams and physico-chemical characteristics of the water. Community composition was analyzed using Non-Metric Multidimensional Scaling (NMDS), and variables related to structural and physico-chemical characteristics were summarized by Principal Component Analysis (PCA). Two explanatory models relating faunal composition to environmental factors were constructed: the first using only continuous variables and the second including the drainage basin as a categorical variable. The Akaike Information Criterion (AIC) and AIC weight were used to select the best model. Although structural and physico-chemical variables significantly contributed to explaining faunal composition, the model including the drainage basin was clearly the better of the two models (more than 90% support in the data). The importance of drainage basins in structuring fish communities in streams may have significant consequences for conservation planning in these environments.
Highlights
The Neotropical region presents a high diversity of freshwater fish, with nearly 4,500 described species and more than 1,550 species still awaiting scientific description (Reis et al, 2003)
This study aims to investigate the effects of level 4 basins from the Plano Nacional de Recursos Hídricos (2003) and the structural and physico-chemical variables of the water on fish community structure in streams of the Madeira-Purus interfluve of the Brazilian Amazon
Our aim is to test which are the most influential factors in structuring the ichthyofauna composition in streams of the MadeiraPurus interfluve: the physical and physico-chemical or the isolation represented by drainage basins
Summary
The Neotropical region presents a high diversity of freshwater fish, with nearly 4,500 described species and more than 1,550 species still awaiting scientific description (Reis et al, 2003). Some studies have shown that the composition of fish communities is distinct in adjacent basins isolated by watershed divisions (Mendonça et al, 2005; Ingenito and Buckup, 2007). In such cases, the watershed acts as a barrier to the dispersal of species between basins. Physical characteristics, such as stream size (Angermeier and Karr, 1984), water velocity (Mendonça et al, 2005), depth (Angermeier and Karr, 1984; Martin-Smith, 1998), and habitat diversity (Gorman and Karr 1978; Angermeier and Schlosser, 1989), or physico-chemical properties, such as electrical conductivity (Taylor et al, 1993; Mérigoux et al, 1998) and pH (Townsend et al, 1983), have been considered to be factors that govern the occurrence and distribution of fish species
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