Research ArticleECOLOGY

Unexpected fish diversity gradients in the Amazon basin

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Science Advances  11 Sep 2019:
Vol. 5, no. 9, eaav8681
DOI: 10.1126/sciadv.aav8681
  • Fig. 1 Sampling sites, species richness, and endemism patterns.

    (A) Fish occurrence records available in the AmazonFish database for each subdrainage basin. Gradients in total species richness (B) and endemism (C) across the 97 subdrainage basins of the Amazon basin. The Amazon basin is flowing West-East to the Atlantic Ocean.

  • Fig. 2 Partial correlation plot (i.e., Pearson residuals) of the distance from river mouth on subdrainage basins total fish species richness after controlling for all other predictors considered in our richness model.

    The overall decrease in sub-basins species richness from upriver to downriver is statistically significant (solid line, table S3) (Pearson’s r = 0.24, P = 0.020, n = 97). Note that removing the outlier sub-basin (red point on top of the graph) from the model changes neither the significance nor the trend of the relationship (Pearson’s r = 0.21, P = 0.040, n = 96). The atypical richness pattern (i.e., a decreasing trend in species richness from upriver to downriver) is depicted for the Amazon main channel (black) and subdrainage basins located north (red) or south (green) of this mainstem and is marginally significant for basins located within the mainstem (Pearson’s r = 0.51, P = 0.089, n = 12) or north (Pearson’s r = 0.36, P = 0.098, n = 22) of the mainstem (red and black dashed lines), but not significant for sub-basins located south of the mainstem (Pearson’s r = 0.13, P = 0.320, n = 63).

  • Fig. 3 Composition of freshwater fishes for the 97 Amazonian subdrainage basins inferred from nonmetric multidimensional scaling ordination using a dissimilarity matrix based on the Simpson's dissimilarity index (βsim), a measure of spatial turnover of species composition without the influence of richness gradients.

    Colors on the map reflect the corresponding point position along both nonmetric multidimensional scaling (NMDS) axes. The analysis depicts stronger dissimilarities in fauna’s composition for the most southeastern part (yellow shades) of the Amazon and the most westerly Andean end (purple and pink shades) compared to the rest of the Basin. The most southeastern part is mainly represented by the Xingu and Tapajós rivers, both hosting a relatively high number of highland endemic species, i.e., 27 endemic species having a geographical distribution restricted above the 300-m elevation. The most westerly Andean end is mainly represented by the Ucayali and Marañón rivers in Peruvian Amazonia and hosts, as for the most southeastern part of the basin, a high number of highland endemic species, i.e., 28 endemic species having a geographical distribution restricted above the 300-m elevation. The red line in the figure at the right indicates the delimitation of the Purus Arch. According to our data, sub-basins located upstream of the Purus Arch (i.e., belonging to the historical Pebas system; fig. S3) currently cover 64% of the total surface area of the entire Amazon basin and host 86% of its total richness (with two families, 72 genera, and 709 species found exclusively in this area), while sub-basins located downstream of the Arch cover only 36% of the total surface and host 68% of the total richness of the basin (with two families, 46 genera, and 313 species found exclusively in this area).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaav8681/DC1

    Fig. S1. Names, sampling effort, and longitudinal position of the 97 sub-basins.

    Fig. S2. Principal water quality of major subdrainages within the Amazon basin.

    Fig. S3. Delimitation of the Pebas lake ∼23 to 10 Ma ago and Purus Arch.

    Fig. S4. Surfaces of the current Amazon basin covered by seawater under 25- and 100-m sea-level rises.

    Table S1. Environmental predictors used to explain fish diversity and endemism in the Amazon basin.

    Table S2. Correlation coefficients among input variables and components for each of the PCAs performed.

    Table S3. Coefficients and SEs from the GLMs performed for total and endemic richness.

    Table S4. Coefficients and SEs (log link scale) from the GLMs for the richness of each of the 15 most abundant families (raw data).

    Table S5. Coefficients and SEs (log link scale) from the GLMs for species richness estimated from SDMs of each of the 15 most abundant families.

    Table S6. Families, genera, and number of species found exclusively west and east of the Purus Arch.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Names, sampling effort, and longitudinal position of the 97 sub-basins.
    • Fig. S2. Principal water quality of major subdrainages within the Amazon basin.
    • Fig. S3. Delimitation of the Pebas lake ∼23 to 10 Ma ago and Purus Arch.
    • Fig. S4. Surfaces of the current Amazon basin covered by seawater under 25- and 100-m sea-level rises.
    • Table S1. Environmental predictors used to explain fish diversity and endemism in the Amazon basin.
    • Table S2. Correlation coefficients among input variables and components for each of the PCAs performed.
    • Table S3. Coefficients and SEs from the GLMs performed for total and endemic richness.
    • Table S4. Coefficients and SEs (log link scale) from the GLMs for the richness of each of the 15 most abundant families (raw data).
    • Table S5. Coefficients and SEs (log link scale) from the GLMs for species richness estimated from SDMs of each of the 15 most abundant families.
    • Table S6. Families, genera, and number of species found exclusively west and east of the Purus Arch.

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