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

Danny Rejas, Monika Winder, Reinaldo Cholima, Thierry Oberdorff

► To cite this version:

Danny Rejas, Monika Winder, Reinaldo Cholima, Thierry Oberdorff. Effects of the non-native Arapaima gigas on native fish species in Amazonian oxbow lakes (Bolivia). PLoS ONE, 2025, 20, 10.1371/journal.pone.0314359. [https://doi.org/10.1371/journal.pone.0314359](https://doi.org/10.1371/journal.pone.0314359). This is an open access article distributed under a Creative Commons Attribution 4.0 International License.

HAL Id: hal-04864905

https://hal.science/hal-04864905v1

Submitted on 5 Jan 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

RESEARCH ARTICLE

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

Danny Rejas¹,²*, Monika Winder¹, Reinaldo Cholima³, Thierry Oberdorff⁴

1 Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden,

2 Unidad de Limnología y Recursos Acuáticos, Universidad Mayor de San Simón, Cochabamba, Bolivia,

3 Centro de Investigación de Recursos Acuáticos, Universidad Autónoma del Beni, José Ballivián, Beni, Bolivia, 4 UMR CRBE (Center for Research on Biodiversity and Environment), CNRS5300, IRD, INP, UPS, Université Paul Sabatier, Toulouse, France

* Danny.Rejas@su.se, Dannyrejas.a@fcyt.umss.edu.bo

## 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.

## Introduction

Introduction of non-native fish species into new environments has become a growing global concern due to their potential ecological effects on recipient ecosystems (see [1] for a review). While these effects may often be subtle, many introductions also exert significant impacts that may range from food webs re-structuring to extirpation of local faunas [2]. *Arapaima gigas*, one of the largest fish in the Amazon Basin, is a prime example of a species introduced outside its natural range primarily for aquaculture, spurred by its significant economic value [3,4]. Originally confined to the floodplains of the Solimões-Amazon, Tocantins-Araguaia and Essequibo Rivers [5,6], *A. gigas* has established populations outside its natural distribution range in

<figure><img src="image_3.png" /></figure>

### OPEN ACCESS

**Citation:** Rejas D, Winder M, Cholima R, Oberdorff T (2025) Effects of the non-native *Arapaima gigas* on native fish species in Amazonian oxbow lakes (Bolivia). PLoS ONE 20(1): e0314359. https://doi.org/10.1371/journal.pone.0314359

**Editor:** Nickson E. Otieno, National Museums of Kenya, KENYA

**Received:** June 25, 2024

**Accepted:** November 8, 2024

**Published:** January 2, 2025

**Copyright:** © 2025 Rejas et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

**Data Availability Statement:** All relevant data are within the manuscript and its Supporting Information files.

**Funding:** This study was funded by the agreement between the Swedish International Development Cooperation Agency (SIDA) (https://www.sida.se/en) and Universidad Mayor de San Simón (UMSS), Project C-26 "Impacto del pez invasor Paiche (Arapaima gigas) sobre peces nativos de la Amazonia boliviana". Preparation of this paper was facilitated by a post-doctoral Grant (GFOv2020-0004) from Wenner-Gren Stiftelserna (Sweden:
https://www.swgc.org/) to D.R. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

**Competing interests:** The authors have declared that no competing interests exist.

Brazil, Perú and Bolivia, where it is claimed to be invasive threatening native fish populations and local ecosystems [3].

The Colonization of Bolivian waters by *A. gigas* originated in the upper Madre de Dios River in Peru, following its introduction on different occasions in several lakes between the mid-1960s and early 1980s with subsequent colonization processes towards the Bolivian territory during flood events. Multiple secondary introductions from aquaculture reinforced this process [7–10]. At present, *A. gigas* has been reported virtually in all the Bolivian tributaries of the Madre de Dios and Orthon Rivers and in the lower reaches of the Beni, Mamoré and Iténez Rivers [10]. The expansion of the colonization into the Mamoré River basin appears to have been dampened by rapids near Guayaramerín. Nonetheless, the colonization of the upper reaches of Mamoré River seems imminent, fueled by unregulated trade and the proliferation of aquaculture activities throughout the region [11].

Although *A. gigas* is often considered an apex predator [10,12,13] due to its large body size and piscivorous habits [14,15], recent studies in both colonized [16] and natural habitats [17,18] reveal that it exhibits high trophic plasticity, acting more as an omnivore with piscivorous tendencies. Moreover, it has been shown that the isotopic niches (a proxy for trophic niche [19–21] of *A. gigas* and of the native fish species inhabiting two recently colonized oxbow lakes of the Madre de Dios River overlapped substantially, suggesting a potential for competition [16]). Yet, niche overlap in itself does not necessarily result in competition when resources are sufficiently abundant [22,23]. To go a step further, here, we compare the TP and isotopic niche width of eleven most abundant native species of diverse trophic levels in two colonized and one currently non-colonized floodplain lakes of the Bolivian Amazon. Given that the broad isotopic niche of *A. gigas* overlaps with the one of most native fish species [16], we hypothesize that *A. gigas* presence may i) decrease TPs of native fishes by forcing them to feed lower on the food chain (i.e. reducing their δ¹⁵N-values [24] and/or ii) reduce their isotopic niche width [22,25] by shrinking their dietary range (i.e. narrowing their range in δ¹³C-values [26]).

## Materials and methods

ULRA/UMSS is an Authorized Scientific Institution (ICA) accredited by the Bolivian Dirección General de la Biodiversidad y Áreas Protegidas (DGBAP) to conduct biological scientific research within the Bolivian territory (Resolución administrativa BMABCC 026/09). Fishes were manipulated according to procedures permitted by the Viceministerio de Medio Ambiente. This study did not involve species classified as either endangered or protected according to the Bolivian red list.

We used stable isotope data of fishes inhabiting one oxbow lake located in the floodplain of Mamoré River and where *A. gigas* was absent. These stable isotope data were compared with recently published data from two oxbow lakes located in the floodplain of Madre de Dios River [16] where *A. gigas* is abundant and represents nearly 50% of the total commercial catches [11]. Samples in the Mamoré River were collected in November 2015 (Lake Tiuco) and samples in the Madre de Dios River were collected in October 2015 (Lake Mentiroso) and July 2017 (Lake Miraflores). Madre de Dios and Mamoré rivers are the main tributaries of the Madera River (Fig 1), both are white-water rivers characterized by turbid, ochre-colored waters with high loads of suspended sediments [27]. White-waters are known to be rich in resources diversity and availability (e.g., nutrients, zooplankton, aquatic insects, fishes) [28], thereby supposedly reducing the likelihood of competitive exclusion [22]. The three sampled lakes were located close to the main channel of the river (< 300 m). The same sampling and stable isotope analyses procedures were applied for the three lakes (described in [16]).
<figure><img src="image_4.png" /><figcaption>**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.</figcaption></figure>

https://doi.org/10.1371/journal.pone.0314359.g001

We collected samples during the low-water period, when floodplain lakes are isolated from the river. Fishes were captured by local fishermen, fishing with hook and lines and a set of gillnets with knot-to-knot distances from 30 to 100 mm. To minimize suffering, recommended humane euthanasia methods for fish were applied. Small and medium-sized specimens were immersed in an ice slurry [29], while large fish were euthanized by percussive stunning, performed by trained fishermen [30].

We collected samples of adult individuals only to avoid potential biases due to species onto-genetic dietary shifts [17]. Mean standard lengths are provided in S1 Table. In total, we captured 20 native fish species, 19 in the colonized lakes (Lakes Mentiroso and Miraflores) and 18 in the non-colonized lake (Lake Tiuco), with 17 species common to both types of lakes. We retained 11 fish species from which we captured sufficient individuals to perform analyses in both locations (≥ 4 individuals). Based on available literature data on gut content analyses [31–33] we further classified these 11 species into four trophic guilds: detritivores, herbivores, invertivores and piscivores to test for differences in TP between trophic guilds and between colonized and non-colonized lakes (Table 1).

For stable isotope analyses, a sample of ~10 g of muscle tissue was taken from the dorsal part of each fish individual. All samples were rinsed with deionized water and stored frozen in cryovials. Posteriorly samples were freeze-dried and ground to a fine powder using a mortar and a pestle. Approximately 1 mg of dry sample material was packed into tin capsules. In addition, we sampled basal carbon sources (C3 and C4 aquatic macrophytes, phytoplankton (as particulate organic matter) and terrestrial vegetation. C3 aquatic macrophytes were not
<table><caption>Table 1. Sample size (n) and mean (± SD) of δ¹³C, δ¹⁵N, δ¹³Ccorr, and trophic position (TP) values, and minimum and maximum δ¹³C and δ¹⁵N values for 11 native fish species from non-colonized (River Mamoré) and colonized (Madre de Dios River) lakes. Species were assigned to trophic guilds based on available literature.</caption><thead><tr><th></th><th>n</th><th>δ¹³C</th><th>δ¹³C<sub>min</sub></th><th>δ¹³C<sub>max</sub></th><th>δ¹³C<sub>corr</sub></th><th>δ¹⁵N</th><th>δ¹⁵N<sub>min</sub></th><th>δ¹⁵N<sub>max</sub></th><th>TP</th></tr></thead><tbody><tr><td colspan="10" style="text-align:center; font-weight:bold;">Non-colonized</td></tr><tr><td>Detritivores</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Potamorhina altamazonica</td><td>8</td><td>-34.0 ± 2.3</td><td>-38.4</td><td>-31.0</td><td>-0.2 ± 0.2</td><td>7.0 ± 0.9</td><td>5.7</td><td>8.6</td><td>2.2 ± 0.3</td></tr><tr><td>Potamorhina latior</td><td>10</td><td>-36.5 ± 1.8</td><td>-39.3</td><td>-33.5</td><td>-0.4 ± 0.1</td><td>7.0 ± 0.6</td><td>6.1</td><td>7.9</td><td>2.2 ± 0.2</td></tr><tr><td>Herbivores</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Colossoma macropomum</td><td>9</td><td>-31.0 ± 2.3</td><td>-35.0</td><td>-28.2</td><td>0.0 ± 0.2</td><td>7.6 ± 1.0</td><td>6.5</td><td>9.2</td><td>2.4 ± 0.4</td></tr><tr><td>Mylossoma duriventre</td><td>13</td><td>-27.9 ± 1.3</td><td>-29.9</td><td>-25.9</td><td>0.3 ± 0.1</td><td>6.9 ± 1.0</td><td>5.1</td><td>8.2</td><td>2.2 ± 0.4</td></tr><tr><td>Piaractus brachypomus</td><td>10</td><td>-30.1 ± 1.8</td><td>-32.0</td><td>-26.9</td><td>0.1 ± 0.1</td><td>6.4 ± 0.7</td><td>5.2</td><td>7.6</td><td>2.0 ± 0.3</td></tr><tr><td>Prochilodus nigricans</td><td>8</td><td>-31.9 ± 2.6</td><td>-35.7</td><td>-28.6</td><td>0.0 ± 0.2</td><td>8.1 ± 0.7</td><td>6.7</td><td>8.8</td><td>2.6 ± 0.3</td></tr><tr><td>Invertivores</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Triportheus albus</td><td>12</td><td>-28.3 ± 1.5</td><td>-32.0</td><td>-26.4</td><td>0.2 ± 0.1</td><td>8.4 ± 0.6</td><td>7.4</td><td>9.3</td><td>2.7 ± 0.2</td></tr><tr><td>Piscivores</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Hoplias malabaricus</td><td>9</td><td>-29.6 ± 1.9</td><td>-33.3</td><td>-27.6</td><td>0.2 ± 0.1</td><td>10.5 ± 0.6</td><td>9.5</td><td>11.4</td><td>3.5 ± 0.2</td></tr><tr><td>Pseudoplatystoma fasciatum</td><td>12</td><td>-29.0 ± 1.3</td><td>-30.8</td><td>-26.5</td><td>0.2 ± 0.1</td><td>10.3 ± 0.7</td><td>9.2</td><td>11.2</td><td>3.4 ± 0.2</td></tr><tr><td>Serrasalmus spilopleura</td><td>10</td><td>-27.1 ± 0.9</td><td>-27.9</td><td>-25.1</td><td>0.3 ± 0.1</td><td>10.3 ± 0.4</td><td>9.6</td><td>11.0</td><td>3.4 ± 0.2</td></tr><tr><td>Plagiscion squamosissimus</td><td>17</td><td>-30.2 ± 1.7</td><td>-33.4</td><td>-27.8</td><td>0.1 ± 0.1</td><td>10.8 ± 0.5</td><td>9.9</td><td>12.0</td><td>3.6 ± 0.2</td></tr><tr><td colspan="10" style="text-align:center; font-weight:bold;">Colonized</td></tr><tr><td>Detritivores</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Potamorhina altamazonica</td><td>10</td><td>-31.8 ± 0.7</td><td>-32.9</td><td>-31.0</td><td>-0.1 ± 0.1</td><td>6.0 ± 0.8</td><td>5.0</td><td>7.3</td><td>2.0 ± 0.3</td></tr><tr><td>Potamorhina latior</td><td>12</td><td>-32.0 ± 1.9</td><td>-34.3</td><td>-28.7</td><td>-0.2 ± 0.2</td><td>6.0 ± 0.9</td><td>4.9</td><td>7.5</td><td>2.0 ± 0.3</td></tr><tr><td>Herbivores</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Colossoma macropomum</td><td>12</td><td>-30.0 ± 1.4</td><td>-32.0</td><td>-28.2</td><td>0.1 ± 0.2</td><td>6.7 ± 0.9</td><td>5.4</td><td>7.8</td><td>2.2 ± 0.3</td></tr><tr><td>Mylossoma duriventre</td><td>13</td><td>-29.0 ± 1.9</td><td>-31.8</td><td>-26.0</td><td>0.2 ± 0.2</td><td>6.8 ± 0.7</td><td>5.8</td><td>7.9</td><td>2.3 ± 0.2</td></tr><tr><td>Piaractus brachypomus</td><td>4</td><td>-30.4 ± 0.5</td><td>-31.1</td><td>-30.0</td><td>0.0 ± 0.1</td><td>7.2 ± 0.5</td><td>6.5</td><td>7.9</td><td>2.4 ± 0.2</td></tr><tr><td>Prochilodus nigricans</td><td>8</td><td>-35.0 ± 1.5</td><td>-37.5</td><td>-32.9</td><td>-0.1 ± 0.1</td><td>8.3 ± 0.4</td><td>7.8</td><td>8.9</td><td>2.0 ± 0.1</td></tr><tr><td>Invertivores</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Triportheus albus</td><td>9</td><td>-31.3 ± 0.9</td><td>-32.7</td><td>-30.2</td><td>-0.1 ± 0.1</td><td>7.6 ± 1.1</td><td>5.2</td><td>9.4</td><td>2.6 ± 0.4</td></tr><tr><td>Piscivores</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Hoplias malabaricus</td><td>5</td><td>-31.8 ± 1.6</td><td>-33.3</td><td>-29.8</td><td>-0.1 ± 0.2</td><td>9.5 ± 0.5</td><td>9.0</td><td>10.1</td><td>3.2 ± 0.2</td></tr><tr><td>Pseudoplatystoma fasciatum</td><td>9</td><td>-33.1 ± 1.3</td><td>-34.7</td><td>-31.3</td><td>-0.3 ± 0.2</td><td>9.0 ± 0.5</td><td>8.2</td><td>9.7</td><td>3.0 ± 0.2</td></tr><tr><td>Serrasalmus spilopleura</td><td>6</td><td>-31.0 ± 1.7</td><td>-33.5</td><td>-29.5</td><td>-0.1 ± 0.2</td><td>8.5 ± 0.5</td><td>8.0</td><td>9.2</td><td>2.9 ± 0.2</td></tr><tr><td>Plagiscion squamosissimus</td><td>17</td><td>-33.7 ± 2.0</td><td>-38.4</td><td>-29.8</td><td>0.0 ± 0.2</td><td>11.6 ± 0.4</td><td>11.0</td><td>12.6</td><td>3.2 ± 0.2</td></tr></tbody></table>

https://doi.org/10.1371/journal.pone.0314359.t001

present in Lake Miraflores during the sampling period). δ¹³C and δ¹⁵N measurements were performed at the UC Davis Stable Isotope Facility laboratory (University of California, Davis, USA).

Stable isotope ratios are reported in parts per thousand (‰) relative to international standards: Pee Dee belemnite (PDB) and atmospheric N for carbon and nitrogen, respectively. Isotope ratios are defined as: δX = (R<sub>sample</sub>/R<sub>standard</sub> - 1) × 10³; where X represents either carbon or nitrogen [34]. When interpreting isotope data, positive δ values indicate a higher proportion of the heavy isotope compared to the standard, while negative δ values indicate a lower proportion [35]. The standard deviations for replicate measurements of standards were ≤0.13‰ and ≤0.10‰ for δ¹³C and δ¹⁵N, respectively.

We used two-way ANOVA to assess interaction effects of lake and basal carbon source on δ¹³C and δ¹⁵N values, using each individual sample as replicates. Since isotopic signatures of basal carbon sources showed spatial variations (see Results), we thus corrected δ¹⁵N and δ¹³C
data for these differences before calculating the isotopic niche width. To this end, we calculated standard ellipse areas (SEAs; [36] metrics using trophic position (TP) instead of δ¹⁵N, and δ¹³Ccorr instead of δ¹³C [37,38]. TP was calculated using the equation: TP = 2 + (δ¹⁵Nfish - δ¹⁵Nbase)/ Δ; where 2 is the TP of the organism used to estimate the baseline (a primary consumer) and Δ is the N isotopic fractionation (in ‰) that occurs between each trophic level [39]. Δ was set at 2.8 ‰ [40]. δ¹⁵Nbase was estimated using mean δ¹⁵N of the primary consumer fish species showing the lowest isotopic δ¹⁵N signal. δ¹³Ccorr was calculated using the equation: δ¹³Ccorr = δ¹³Cfish - δ¹³Cmpc / CRpc. Where δ¹³Cfish is the carbon isotope signal of the focal fish species; δ¹³Cmpc is the mean primary consumer carbon isotope signal and CRpc is the carbon range (δ¹³Cmax - δ¹³Cmin) for all herbivore and detritivore individuals sampled. We used primary consumers as baselines because they integrate spatial and temporal variations in the isotopic signatures of primary producers [39]. δ¹⁵Nbase, δ¹³Ccorr, δ¹³Cmpc, and CRpc were estimated for each individual lake. Lake had no significant effect (ANOVA, p > 0.05) on mean TP and δ¹³Ccorr when comparing colonized lakes (Mentiroso and Miraflores), thus, data from both colonized lakes were combined for posterior analyses. To estimate the relative contribution of detritivorous, herbivorous and invertivorous fishes to the dietary composition of piscivorous fishes in non-colonized and colonized environments, we fitted Bayesian isotope mixing models using the package “MixSIAR” [41]. Mean trophic discrimination factor (TDF) values were set to 1.3 (SD = 0.3) ‰ and 2.8 (SD = 0.4) ‰ for δ¹³C and δ¹⁵N, respectively [40]. Data are provided in S2 Table, data from the colonized Lake Miraflores were excluded from this analysis due to the lack of sample from all prey fish guilds.

We used two-way ANOVA to assess interaction effects of lake type (colonized / non-colonized) and trophic guilds on TP using each fish individual as replicates. We then tested for differences in TP between trophic guilds within each of the lake types using one-way ANOVAs followed by Tukey's HSD test. Before each ANOVA test performed, we verified data for normality using Shapiro-Wilk test. We calculated isotopic niche widths using the “Stable Isotope Bayesian Ellipses” in the R package SIBER [36]. The program calculates metrics describing the data in a δ¹³C - δ¹⁵N space for each lake fish populations: i.e., the total amount of isotopic niche area occupied (total area; TA), the SEA and the sample size-corrected SEA (SEAc). To test whether the isotopic niches of species from colonized and non-colonized lakes differed, Bayesian inference was used to generate a distribution of covariance matrices (based on 10,000 posterior draws) that describe the observed data, and to calculate the posterior Bayesian estimates of the SEA (SEAb). We calculated the probability that SEAb in colonized environments is smaller or larger than SEAb in the non-colonized environment by comparing each pair of posterior draws and determining which is smaller or larger. The proportion of draws that are smaller (or larger) is a direct proxy for the probability of one group's posterior distribution SEAb to be smaller (or larger) than the other [36,42,43]. All Data analyses were performed using R 4.2.2 [44].

## Results

A comparison of δ¹³C and δ¹⁵N values across the three lakes studied revealed that basal carbon sources tended to show lower δ¹³C values in Lake Miraflores, while Lake Tiuco showed higher δ¹⁵N values (S3 Table). Significant interaction effects between lakes and basal carbon sources were detected for both δ¹³C and δ¹⁵N isotopes (two-way ANOVA, p-values < 0.001) (S4 Table).

Primary consumers (i.e. herbivorous and detritivorous fish species) were at the bottom of the food chain with TPs varying from 2.0 to 2.6. The invertivorous fish *Triportheus albus* showed intermediate TP values from 2.6 to 2.7, and the piscivorous species showed the highest
<table><caption>**Table 2.** Proportional contribution (median [Mdn], standard deviation [SD], and 95% credible intervals [CI]) of prey groups to the diet of piscivorous fishes in *A. gigas* colonized and non-colonized lakes in the Bolivian Amazon basin.</caption><thead><tr><th rowspan="2"></th><th colspan="2">Non-colonized</th><th colspan="2">Colonized</th></tr><tr><th>n</th><th>Mdn (SD) [95% CI]</th><th>n</th><th>Mdn (SD) [95% CI]</th></tr></thead><tbody><tr><td>Detritivores</td><td>18</td><td>0.15 (0.16) [0.00–0.54]</td><td>22</td><td>1.00 (0.07) [0.80–1.00]</td></tr><tr><td>Herbivores</td><td>40</td><td>0.28 (0.33) [0.00–1.00]</td><td>29</td><td>0.00 (0.04) [0.00–0.08]</td></tr><tr><td>Invertivores</td><td>12</td><td>0.49 (0.28) [0.00–0.96]</td><td>9</td><td>0.00 (0.06) [0.00–0.16]</td></tr></tbody></table>

https://doi.org/10.1371/journal.pone.0314359.t002

TPs varying from 2.9 to 3.6 (Table 1). Significant interaction effects between trophic guilds and types of lake were identified for TP (two-way ANOVA, p < 0.05), showing that the effect of trophic guilds on TP values varied between types of lakes (S5 Table). Subsequent analyses were performed independently for each type of lake. Significant differences among fish trophic guilds were observed within colonized lakes, with detritivores exhibiting the lowest trophic level, followed by herbivores, invertivores, and finally piscivores (p-values < 0.05). This pattern remained similar in the non-colonized lake except that detritivores and herbivores TPs were not significantly different (p = 0.8) (S6 Table). Pairwise comparisons of TP in colonized and non-colonized lakes for each trophic guild showed no significant differences (p-values > 0.05) except for piscivorous fishes, the species belonging to this guild exhibiting significantly higher TPs in non-colonized compared to colonized lakes (p < 0.001; Tables 1 and S5). For piscivores from the non-colonized Lake Tiuco, median posterior estimates from isotope mixing models indicated that invertivorous prey-fish comprised the largest proportion of the diet (49%), followed by detritivorous and herbivorous prey-fish that contributed approximately 15% and 28%, respectively. In the colonized Lake Mentiroso, the diet of piscivorous fishes shifted towards a predominant consumption of detritivorous prey-fish that represented between 80% and 100% of the diet (Table 2).

SIBER analyses revealed that, irrespective of their trophic guild affiliation, the isotopic niche width of the majority of species did not exhibit significant differences between lakes colonized by *A. gigas* and the non-colonized lake (eight out of eleven species) (SEAb, 0.05 < p < 0.95). For two species, namely the detritivore *Potamorhina latior* and the piscivore *Serrasalmus spilopleura*, the isotopic niche width was significantly larger in the colonized environment (p-values < 0.05) and only one species, the herbivore *Piaractus brachipomus* (p = 0.97) showed a smaller isotopic niche width in the colonized environment compared to the non-colonized one (Table 3, Figs 2–4). However, concerning this last species, the smaller isotopic niche width noticed in the colonized environment compared to the non-colonized one is most probably the result of a niche width underestimation due to the small sample size (only 4 individuals sampled in the colonized lake), as SEA is strongly influenced by the number of individuals included in its calculation [45].

## Discussion

Here we investigated the potential influence of the non-native fish *Arapaima gigas* on TP and isotopic niche width of native fish species by comparing colonized (Madre de Dios River) and non-colonized lakes (Mamoré River). Our study reveals, regardless of the presence of *A. gigas*, a robust alignment between TP values and the trophic guilds determined *a priori* from literature, with primary consumers (detritivores and herbivores) showing the lowest values, invertivorous species intermediate values, and piscivorous species showing the highest values. However, significant lower TP values were noticed for piscivorous species inhabiting colonized lakes compared to the non-colonized lake. Our estimations of the relative contribution of the
<table><caption>Table 3. Isotopic niche area (‰²) estimates for native fish species from non-colonized (River Mamoré) and colonized (Madre de Dios River) lakes.</caption><thead><tr><th></th><th>TA</th><th>SEA</th><th>SEAc</th><th>SEAb</th><th>95% CI</th></tr></thead><tbody><tr><td colspan="6" style="text-align: center;">Non-colonized lakes</td></tr><tr><td>Detritivores</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Potamorhina altamazonica</em></td><td>0.21</td><td>0.13</td><td>0.16</td><td>0.14</td><td>0.06-0.29</td></tr><tr><td><em>Potamorhina latior</em></td><td>0.15</td><td>0.07</td><td>0.08</td><td>0.07</td><td>0.04-0.14</td></tr><tr><td>Herbivores</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Colossoma macropomum</em></td><td>0.25</td><td>0.15</td><td>0.17</td><td>0.14</td><td>0.08-0.31</td></tr><tr><td><em>Mylossoma duriventre</em></td><td>0.22</td><td>0.11</td><td>0.12</td><td>0.10</td><td>0.06-0.19</td></tr><tr><td><em>Piaractus brachypomus</em></td><td>0.20</td><td>0.11</td><td>0.12</td><td>0.10</td><td>0.06-0.21</td></tr><tr><td><em>Prochilodus nigricans</em></td><td>0.21</td><td>0.13</td><td>0.15</td><td>0.13</td><td>0.06-0.28</td></tr><tr><td>Invertivores</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Triportheus albus</em></td><td>0.16</td><td>0.07</td><td>0.08</td><td>0.07</td><td>0.04-0.12</td></tr><tr><td>Piscivores</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Hoplias malabaricus</em></td><td>0.20</td><td>0.11</td><td>0.13</td><td>0.10</td><td>0.05-0.21</td></tr><tr><td><em>Pseudoplatystoma fasciatum</em></td><td>0.14</td><td>0.07</td><td>0.08</td><td>0.06</td><td>0.04-0.12</td></tr><tr><td><em>Serrasalmus spilopleura</em></td><td>0.05</td><td>0.03</td><td>0.03</td><td>0.02</td><td>0.01-0.06</td></tr><tr><td><em>Plagioscion squamosissimus</em></td><td>0.18</td><td>0.07</td><td>0.08</td><td>0.07</td><td>0.04-0.12</td></tr><tr><td colspan="6" style="text-align: center;">Colonized lakes</td></tr><tr><td>Detritivores</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Potamorhina altamazonica</em></td><td>0.11</td><td>0.07</td><td>0.08</td><td>0.06</td><td>0.04-0.14</td></tr><tr><td><em>Potamorhina latior</em></td><td>0.38</td><td>0.20</td><td>0.22</td><td>0.19</td><td>0.11-0.35</td></tr><tr><td>Herbivores</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Colossoma macropomum</em></td><td>0.11</td><td>0.06</td><td>0.07</td><td>0.08</td><td>0.04-0.15</td></tr><tr><td><em>Mylossoma duriventre</em></td><td>0.37</td><td>0.18</td><td>0.20</td><td>0.17</td><td>0.10-0.31</td></tr><tr><td><em>Piaractus brachypomus</em></td><td>0.01</td><td>0.02</td><td>0.03</td><td>0.03</td><td>0.01-0.09</td></tr><tr><td><em>Prochilodus nigricans</em></td><td>0.10</td><td>0.06</td><td>0.07</td><td>0.06</td><td>0.03-0.13</td></tr><tr><td>Invertivores</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Triportheus albus</em></td><td>0.25</td><td>0.14</td><td>0.16</td><td>0.13</td><td>0.07-0.27</td></tr><tr><td>Piscivores</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Hoplias malabaricus</em></td><td>0.08</td><td>0.08</td><td>0.10</td><td>0.07</td><td>0.03-0.21</td></tr><tr><td><em>Pseudoplatystoma fasciatum</em></td><td>0.10</td><td>0.06</td><td>0.07</td><td>0.06</td><td>0.03-0.13</td></tr><tr><td><em>Serrasalmus spilopleura</em></td><td>0.11</td><td>0.09</td><td>0.12</td><td>0.08</td><td>0.04-0.22</td></tr><tr><td><em>Plagioscion squamosissimus</em></td><td>0.22</td><td>0.09</td><td>0.10</td><td>0.09</td><td>0.05-0.15</td></tr></tbody></table>

Estimates of isotopic niche area are given as total area (TA), standard ellipse area (SEA), sample size-corrected standard ellipse area (SEAc) and the mode of the Bayesian (posterior) standard ellipse area (SEAb) estimates. Upper and lower 95% credible intervals (CI) indicate the uncertainty in the SEAb estimates calculated from the posterior distributions of the fitted ellipses.

https://doi.org/10.1371/journal.pone.0314359.t003

different fish guilds to the diet of piscivorous fish showed that this decreasing tendency in TP values was caused by a shift in the diet of piscivorous species toward prey-fish located lower in the food chain, with detritivorous fishes representing the largest proportion of their diet in the colonized Lake Mentiroso. These findings align with previous research suggesting that introduced species can sometimes force native species to feed on lower trophic levels [24,46].

Such alterations in trophic dynamics may stem from non-exclusive mechanisms such as interference competition (i.e. *A. gigas*, as a territorial and dominant species, may force other piscivores to use poorer foraging areas) and/or induced scarcity of prey resources (i.e. fewer prey-fish individuals available in colonized lakes). The first mechanism described above probably acts in our case as we also observed a shift towards lower δ¹³Ccorr values for piscivorous
<figure><img src="image_5.png" /><figcaption>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 δ¹³Ccorr 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).</figcaption></figure>

https://doi.org/10.1371/journal.pone.0314359.g002
<figure><img src="image_6.png" /><figcaption>**Fig 3.** Isotopic niche of four native fish species (piscivorous) in *Arapaima gigas* colonized and non-colonized lakes. Isotopic niche estimated from δ¹³Ccorr 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).</figcaption></figure>

https://doi.org/10.1371/journal.pone.0314359.g003

species in colonized compared to the non-colonized lakes (see Fig 3), suggesting a displacement of these species to different and potentially sub-optimal feeding habitats. The fact that lower TPs were found for piscivorous species but not for species belonging to the remaining trophic guilds is consistent with *A. gigas* feeding habits (a generalist species with piscivorous tendencies [16,18,47]) as resources are supposed to be sufficiently abundant in the three lakes to reduce the likelihood of direct competition.

Conversely, the isotopic niche width did not differ significantly between species occurring in *A. gigas* colonized and non-colonized environments. These findings contrast with our original hypothesis predicting a reduction in the isotopic niche width of native species due to potential competition and resource constraints imposed by *A. gigas* in the colonized lakes [24,26]. Even if the absence of a significant reduction in isotopic niche widths despite high niche overlaps between native fish species and *A. gigas* [16] cannot formally be interpreted as an absence of competitive interaction between *A. gigas* and native fish assemblages, this absence of niche width reduction allows at least to conclude that trophic niche space of native fishes is resistant to change from colonization by *A. gigas*. Due to the historical presence and diversity of piscivores in the native fish assemblages [32,48,49], prey-fish may have developed effective antipredator strategies prior to colonization, potentially reducing the impact of this new predator [50,51].
<figure><img src="image_7.png" /><figcaption>**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 dots 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.</figcaption></figure>

https://doi.org/10.1371/journal.pone.0314359.g004

While we acknowledge that our study suffers limitation concerning sample size (i.e. number of lakes and species analyzed, number of individuals sampled) and that the isotopic niche needs to be interpreted with caution as it does not fully reflect the true trophic niche of species [21], our results based on species TP and isotopic niche width suggest that the ecological
impact of *A. gigas* on native fish in the two colonized lakes is rather weak for most native species. However, there is a notable exception for piscivores, which exhibit a significant decline in TP following *A. gigas* establishment. Further analyses on potential indirect effects, such as changes in community and/or food web structure following *A. gigas* colonization may provide valuable insights into other potential ecological impacts that this introduced species may generate in Bolivian waters.

**Supporting information**

S1 Table. Number of individuals (n), standard length (SL) and standard deviation (SD) of fish captured in lakes colonized and non-colonized by *Arapaima gigas*, located in the floodplains of rivers Mamore and Madre de Dios, respectively.

(DOCX)

S2 Table. Number of individuals (n), mean, median (Mdn), standard deviation (SD) and confidence intervals (CI) for fish trophic guilds sampled in lakes colonized and non-colonized by *Arapaima gigas*, located in the floodplains of rivers Mamore and Madre de Dios, respectively.

(DOCX)

S3 Table. Sample size (n) and mean δ¹³C and δ¹⁵N values (± SD) for the carbon sources from non-colonized (Lake Tiuco) and *Arapaima gigas* colonized lakes (Lakes Mentiroso and Miraflores), located in the floodplains of rivers Mamore and Madre de Dios, respectively.

(DOCX)

S4 Table. Results of two-way ANOVA, testing the effect of basal carbon source (C4-macrophytes, C3-macrophytes, POM, and terrestrial vegetation) and lake on δ¹³C and δ¹⁵N values. Significant differences for: *P*<0.05; **P*<0.01; ***P*<0.001.

(DOCX)

S5 Table. Results of two-way ANOVA, testing the effect of ‘trophic guild’ (detritivores, herbivores, invertivores and piscivores) and ‘Type of lake’ (colonized and non-colonized by *Arapaima gigas*) on trophic position (TP); and post hoc Tukey’s HSD tests pairwise comparisons of trophic guilds in colonized and non-colonized lakes. Significant differences for: *P*<0.05; **P*<0.01; ***P*<0.001; NS: no significant differences for P>0.05.

(DOCX)

S6 Table. Results of one-way ANOVAs and post hoc Tukey's HSD test, testing for the effect of “trophic guild” on TP in lakes colonized and non-colonized by *Arapaima gigas*. Significant differences for: *P*<0.05; **P*<0.01; ***P*<0.001; N.S.: no significant differences for P>0.05.

(DOCX)

**Acknowledgments**

We would like to thank the Fishermen from Trinidad for their valuable help in the field. We thank Pablo Prado for editing the map.

**Author Contributions**

Conceptualization: Danny Rejas.
**Data curation:** Danny Rejas.

**Formal analysis:** Danny Rejas, Monika Winder.

**Funding acquisition:** Danny Rejas.

**Investigation:** Danny Rejas, Reinaldo Cholima, Thierry Oberdorff.

**Methodology:** Danny Rejas, Thierry Oberdorff.

**Project administration:** Danny Rejas.

**Software:** Danny Rejas.

**Supervision:** Monika Winder, Thierry Oberdorff.

**Validation:** Reinaldo Cholima, Thierry Oberdorff.

**Visualization:** Monika Winder, Thierry Oberdorff.

**Writing – original draft:** Danny Rejas.

**Writing – review & editing:** Danny Rejas, Monika Winder, Reinaldo Cholima, Thierry Oberdorff.

## References

1. Bernery C, Bellard C, Courchamp F, Brosse S, Gozlan RE, Jaric IJ, et al. Freshwater fish invasions: A comprehensive review. Annual Review of Ecology, Evolution, and Systematics. 2022; 53: 427–456. https://doi.org/10.1146/annurev-ecolsys-032522

2. Cucherousset J, Olden JD. Ecological impacts of non-native freshwater fishes. Fisheries (Bethesda). 2011; 36: 15–30.

3. Pereira LS, Barbosa JM, Souza RGC. The Amazonian *Arapaima* changes its status from threatened species to an invader of earth's freshwater ecosystems. Acta of Fisheries and Aquatic Resources. 2022; 10: 97–107. https://doi.org/10.46732/actafish.2022.10.2.97–107

4. Hrbek T, Crossa M, Farias I. Conservation strategies for Arapaima gigas (Schninz, 1822) and the Amazonian várzea ecosystem. Braz J Biol. 2007; 67: 909–917. https://doi.org/10.1590/s1519-69842007000500015 PMID: 18278359

5. Castello L, Stewart DJ. Assessing CITES non-detriment findings procedures for *Arapaima* in Brazil. Journal of Applied Ichthyology. 2010; 26: 49–56.

6. Dubos N, Lenormand M, Castello L, Oberdorff T, Guisan A, Luque S. Protection gaps in Amazon flood-plains will increase with climate change: Insight from the world's largest scaled freshwater fish. Aquat Conserv. 2022; 32: 1830–1841. https://doi.org/10.1002/aqc.3877

7. Carvajal-Vallejos F, Van Damme P, Cordova L, Coca C. La introducción de *Arapaima gigas* (Paiche) en la Amazonía Boliviana. Los peces y delfines de la Amazonía boliviana: hábitats, potencialidades y amenazas. 2011. pp. 367–396.

8. Miranda-Chumacero G, Wallace R, Calderón H, Calderón G, Willink P, Guerrero M, et al. Distribution of arapaima (*Arapaima gigas*) (Pisces: Arapaimatidae) in Bolivia: implications in the control and management of a non-native population. 2012; 1: 129–138.

9. Farias IP, Willis S, Leão A, Verba JT, Crossa M, Foresti F, et al. The largest fish in the world's biggest river: Genetic connectivity and conservation of *Arapaima gigas* in the Amazon and Araguaia-Tocantins drainages. PLoS One. 2019; 14: e0220882–. Available: https://doi.org/10.1371/journal.pone.0220882

10. Catâneo DTB dos S, Ximenes AM, Garcia-Davila CR, Van Damme PA, Pagotto R de C, Vitule JRS, et al. Elucidating a history of invasion: population genetics of pirarucu (*Arapaima gigas*, Actinopterygii, Arapaimidae) in the Madeira River. Hydrobiologia. 2022; 849: 3617–3632. https://doi.org/10.1007/s10750-022-04977-8

11. Van Damme PA, Méndez CC, Zapata M, Carvajal-Vallejos FM, Carolsfeld J, Olden JD. The expansion of Arapaima cf. gigas (osteoglossiformes: Arapaimidae) in the Bolivian Amazon as informed by citizen and formal science. Management of Biological Invasions. 2015; 6: 375–383. https://doi.org/10.3391/mbi.2015.6.4.06
12. Doria CR da C, Catâneo DTBDS, Torrente-Vilara G, Vitule JRS. Is there a future for artisanal fishing in the amazon? The case of *Arapaima gigas*. Management of Biological Invasions. 2020; 11: 1–8. https://doi.org/10.3391/mbi.2020.11.1.01

13. Campos-Silva JV, Peres CA. Community-based management induces rapid recovery of a high-value tropical freshwater fishery. Sci Rep. 2016; 6. https://doi.org/10.1038/srep34745 PMID: 27731319

14. Lüling KH. Zur biologie und ökologie von *Arapaima gigas* (Pisces, Osteoglossidae). Zeitschrift für Morphologie und Ökologie der Tiere. 1964; 54: 436–530.

15. Romero JS. El paiche, aspectos de su historia natural, ecología y aprovechamiento. Inf. Servicio Pesquerías y Caza Ministerio de Agricultura Lima-Perú. 1960; 63.

16. Rejas D, Oberdorff T, Declerck SAJ, Winder M. The introduced *Arapaima gigas* in the Bolivian Amazon: Trophic position and isotopic niche overlap with native species. Ecol Freshw Fish. 2023; 32: 926–937. https://doi.org/10.1111/eff.12734

17. Carvalho F, Power M, Forsberg BR, Castello L, Martins EG, Freitas CEC. Trophic Ecology of *Arapaima* sp. in a ria lake—river–floodplain transition zone of the Amazon. Ecol Freshw Fish. 2018; 27: 237–246. https://doi.org/10.1111/eff.12341

18. Watson LC, Stewart DJ, Teece MA. Trophic ecology of *Arapaima* in Guyana: giant omnivores in Neotropical floodplains. Neotropical Ichthyology. 2013; 11: 341–349.

19. Pagani-Núñez E, Renom M, Furquet C, Rodríguez J, Llimona F, Senar JC. Isotopic niche overlap between the invasive leiothrix and potential native competitors. Anim Biodivers Conserv. 2018; 41: 427–434. https://doi.org/10.32800/abc.2018.41.0427

20. Jackson MC, Donohue I, Jackson AL, Britton JR, Harper DM, Grey J. Population-level metrics of trophic structure based on stable isotopes and their application to invasion ecology. PLoS One. 2012; 7. https://doi.org/10.1371/journal.pone.0031757 PMID: 22363724

21. Karlson AML, Gorokhova E, Elmgren R. Do deposit-feeders compete? Isotopic niche analysis of an invasion in a species-poor system. Sci Rep. 2015; 5. https://doi.org/10.1038/srep09715 PMID: 25988260

22. Alley TR. Competition theory, evolution, and the concept of an ecological niche. Acta Biotheor. 1982; 31: 165–179. https://doi.org/10.1007/BF01857239 PMID: 6815945

23. Pianka ER. Niche Overlap and Diffuse Competition. Proceedings of the National Academy of Sciences. 1974; 71: 2141–2145. https://doi.org/10.1073/pnas.71.5.2141 PMID: 4525324

24. Marks JC, Haden GA, O'Neill M, Pace C. Effects of Flow Restoration and Exotic Species Removal on Recovery of Native Fish: Lessons from a Dam Decommissioning. Restor Ecol. 2010; 18: 934–943. https://doi.org/10.1111/j.1526-100X.2009.00574.x

25. Christiansen FB, Fenchel TM. Theories of populations in biological communities. Theories of Populations in Biological Communities. Heidelberg: Springer Verlag; 1977.

26. Pilger TJ, Gido KB, Propst DL. Diet and trophic niche overlap of native and nonnative fishes in the Gila River, USA: Implications for native fish conservation. Ecol Freshw Fish. 2010; 19: 300–321. https://doi.org/10.1111/j.1600-0633.2010.00415.x

27. Sioli H. The Amazon: limnology and landscape ecology of a mighty tropical river and its basin. Dorrecht, NL: Junk Publishers; 1984.

28. Fernandes CC, Podos J, Lundberg JG. Amazonian ecology: tributaries enhance the diversity of electric fishes. Science. 2004; 305: 1960–1962. https://doi.org/10.1126/science.1101240 PMID: 15448270

29. Blessing JJ, Marshall JC, Balcombe SR. Humane killing of fishes for scientific research: a comparison of two methods. J Fish Biol. 2010; 76: 2571–2577. https://doi.org/10.1111/j.1095-8649.2010.02633.x PMID: 20557609

30. Sundell E, Brijs J, Gräns A. The quest for a humane protocol for stunning and killing Nile tilapia (Oreochromis niloticus). Aquaculture. 2024; 593: 741317.

31. De Mérona B, Rankin-de-Mérona J. Food resource partitioning in a fish community of central Amazon floodplain. Neotropical Ichthyology. 2004; 2: 75–84.

32. Pouilly M, Yunoki T, Rosales C, Torres L. Trophic structure of fish assemblages from Mamoré River floodplain lakes (Bolivia). Ecol Freshw Fish. 2004; 13: 245–257. Available: http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0633.2004.00055.x/full.

33. Sarmiento J, Bigorne R, Carvajal-Vallejos FM, Maldonado M, Leciak E, Oberdorff T. Peces de Bolivia/ Bolivian fishes. 2014. IRD Éditions.

34. Fry B. Stable isotope ecology. New York: Springer; 2006.

35. Jepsen DB, Winemiller KO. Structure of tropical river food webs revealed by stable isotope ratios. Oikos. 2002; 96: 46–55. https://doi.org/10.1034/j.1600-0706.2002.960105.x
36. Jackson AL, Inger R, Parnell AC, Bearhop S. Comparing isotopic niche widths among and within communities: SIBER—Stable Isotope Bayesian Ellipses in R. Journal of Animal Ecology. 2011; 80: 595–602. https://doi.org/10.1111/j.1365-2656.2011.01806.x PMID: 21401589

37. Olsson K, Stenroth P, Nyström P, Granéli W. Invasions and niche width: Does niche width of an introduced crayfish differ from a native crayfish? Freshw Biol. 2009; 54: 1731–1740. https://doi.org/10.1111/j.1365-2427.2009.02221.x

38. Richoux NB, Ndhlovu RT. Temporal variability in the isotopic niches of rocky shore grazers and suspension-feeders. Marine Ecology. 2015; 36: 1045–1059. https://doi.org/10.1111/maec.12200

39. Post DM. Using stable isotopes to estimate trophic position: models, methods, and assumptions. Ecology. 2002; 83: 703–718. https://doi.org/10.2307/3071875

40. McCutchan JH Jr, Lewis WM Jr, Kendall C, McGrath CC. Variation in trophic shift for stable isotope ratios of carbon, nitrogen, and sulfur. Oikos. 2003; 2: 378–390.

41. Stock BC, Jackson AL, Ward EJ, Parnell AC, Phillips DL, Semmens BX. Analyzing mixing systems using a new generation of Bayesian tracer mixing models. PeerJ. 2018; 2018. https://doi.org/10.7717/peerj.5096 PMID: 29942712

42. Ferreira RL, Ceia FR, Borges TC, Ramos JA, Bolten AB. Foraging niche segregation between juvenile and adult hawksbill turtles (Eretmochelys imbricata) at Príncipe island, West Africa. J Exp Mar Biol Ecol. 2018; 498: 1–7. https://doi.org/10.1016/j.jembe.2017.10.005

43. Young H, Nigro K, McCauley DJ, Ballance LT, Oleson EM, Baumann-Pickering S. Limited trophic partitioning among sympatric delphinids off a tropical oceanic atoll. PLoS One. 2017; 12: e0181526. https://doi.org/10.1371/journal.pone.0181526 PMID: 28767677

44. R Core Team. R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2022. Available: http://www.r-project.org/.

45. Syväranta J, Lensu A, Marjomäki TJ, Oksanen S, Jones RI. An empirical evaluation of the utility of convex hull and standard ellipse areas for assessing population niche widths from stable isotope data. PLoS One. 2013; 8: e56094. https://doi.org/10.1371/journal.pone.0056094 PMID: 23405254

46. Vander Zanden MJ, Casselman JM, Rasmussen JB. Stable isotope evidence for the food web consequences of species invasions in lakes. Nature. 1999; 401: 464–467.

47. Villafan S, Aguilar F, Barrozo D, Argote A, Lizarro Dennis, Maldonado M, et al. Dieta y posición trófica del Paiche (*Arapaima gigas*) en lagunas meándricas de la Amazonia boliviana. Hidrobiología Neotropical y Conservación Acuática. 2020; 1: 42–58.

48. Rejas D. Trophic structure of a floodplain fish assemblage in the upper Amazon basin, Bolivia. Rev Biol Trop. 2018; 66: 1258–1271. https://doi.org/10.15517/rbt.v66i3.30693

49. Rejas D, Maldonado M. Variaciones espacio-temporales de la composición de la comunidad de peces de una laguna de la várzea del río Ichilo (Cochabamba, Bolivia). Revista Boliviana de Ecología y Conservación. 2000; 7: 37–46.

50. Levine JM. Biological invasions. Current Biology. 2008; 18: R57–R60. https://doi.org/10.1016/j.cub.2007.11.030 PMID: 18211837

51. Sih A, Bolnick DI, Luttbeg B, Orrock JL, Peacor SD, Pintor LM, et al. Predator-prey naïveté, antipredator behavior, and the ecology of predator invasions. Oikos. 2010; 119: 610–621. https://doi.org/10.1111/j.l