Effects of the non-native Arapaima gigas on native fish species in Amazonian oxbow lakes (Bolivia)

Abstract

The introduction of non-native fish species into new environments has raised global concerns due to potential ecological impacts on recipient ecosystems. A previous study focusing on the introduced fish species Arapaima gigas in Bolivian Amazon waters showed that its isotopic niche significantly overlapped with most co-occurring native fish species, suggesting potential competition. To evaluate this hypothesis, we extended here the investigation by comparing the trophic position and isotopic niche width of eleven abundant native fish species inhabiting both colonized and non-colonized floodplain lakes. We found lower trophic positions in colonized versus non-colonized lakes only for native piscivores, mostly driven by a shift towards increased dietary proportion of detritivorous fishes. Conversely, results showed that the isotopic niche width of most fish species analyzed (i.e. 10 over 11 species) did not significantly decrease in colonized compared to non-colonized lakes. Our overall results suggest potentially low competitive interactions between A. gigas and native fishes, with the notable exception of piscivorous species. We attribute our findings to the high abundance of available resources in Amazon oxbow lakes.

Fig 1. Study area.

Location of the lakes studied (black filled) in the floodplain of Madre de Dios and Mamoré rivers in Bolivia, South America. The black arrow shows the direction of colonization of Arapaima gigas. Redrawn from OpenStreetMap data (© OpenStreetMap contributors, licensed under ODbL) and partially adapted from Rejas et al. 2023 [16] © 2023 Published by John Wiley & Sons Ltd. under the terms of the Creative Commons Attribution License CC BY 4.0.

Fig 2. Isotopic niche of seven native fish species (detritivorous, herbivorous and invertivorous) in Arapaima gigas colonized and non-colonized lakes.

Isotopic niche estimated from δ¹³C_corr and TP values for native detritivorous (a, b), herbivorous (c, d, e, f) and invertivorous (g) fish species. Each symbol (circles and triangles) represents an individual fish, while the ellipses denote the 95% credible interval. Circles and solid lines represent fish from the non-colonized lake (Mamoré River), and triangles and dashed lines represent fish from colonized lakes (Madre de Dios River).

Fig 3. Isotopic niche of four native fish species (piscivorous) in Arapaima gigas colonized and non-colonized lakes.

Isotopic niche estimated from δ¹³C_corr and TP values for native piscivorous fish species. Each symbol (circles and triangles) represents an individual fish, while the ellipses denote the 95% credible interval. Circles and solid lines represent fish from the non-colonized lake (Mamoré River), and triangles with dashed lines represent fish from colonized lakes (Madre de Dios River).

Fig 4. Estimated niche width for 11 native fish species in Arapaima gigas colonized and non-colonized lakes.

Boxplots of the Bayesian posterior estimates of Bayesian Standard Ellipse Area (SEAb) native fish species in A. gigas colonized (C) and non-colonized (NC) lakes. Black dotes represent the mode, shaded boxes represent the 50%, 75% and 95% credible intervals from dark to light grey. P is the probability that SEAb in the colonized lakes is smaller than in the non-colonized one. A p-value ≤ 0.05 indicates a significantly smaller SEAb within the colonized lakes compared to the non-colonized one. P-values > 0.05 and < 0.95 indicate no significant difference in SEAb, while p-values ≥ 0.95 indicate a significantly smaller SEAb in the non-colonized site. Figures a (P. altamazonica) and b (P. latior) represent detritivorous species; figures c (C. macropomum), d (M. duriventre), e (P. brachipomus) and f (P. nigricans) represent herbivorous species; figure g (T. albus) represents invertivorous species; and figures h (H. malabaricus), i (P. fasciatum), j (S. spilopleura) and k (P. squamosissimus) represent piscivorous species.