10 results on '"Araújo, Francisco Gerson"'
Search Results
2. Cannibalism facilitates and sustains the invasion of top‐predator fish (Cichlidae: Cichla) in human‐modified ecosystems.
- Author
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Guedes, Gustavo Henrique Soares, Franco, Ana Clara Sampaio, dos Santos, Luciano Neves, dos Santos, Alejandra Filippo Gonzalez Neves, and Araújo, Francisco Gerson
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PREDATION ,CANNIBALISM ,PREY availability ,CICHLIDS ,TEMPORAL databases ,TOP predators ,INTRODUCED species - Abstract
The strategies that allow invasive alien species to perpetuate themselves in the long term are still poorly understood in invasion science. Considering top predators, a key issue is how they overcome the prey decline which they have caused during the invasion process. We investigate factors related to the persistence, impacts and long‐term success of the emerging peacock bass (Cichlidae: Cichla) invasion, a fish native to the Amazon biome that has been introduced globally.We analysed a robust temporal database that includes comparisons (1994–2002 vs. 2015–2017) on the diet of Cichla ocellaris, the abundance of this invader, its prey and competitors in a human‐modified ecosystem. In addition, we compare the frequency of cannibalism (presence or absence) between native versus non‐native populations, and between natural versus human‐modified ecosystems in the American continent. Four hypotheses were tested: (i) prey and competitor populations decrease through time as a result of predation impacts; (ii) cannibalism is size‐ and density‐dependent, and increases after native prey decline; (iii) cannibalism is more frequent in non‐native populations; and (iv) the abundance of invader decreases over time because of reduced resources and increased cannibalism.Our results revealed that the impacts of introducing this predator into communities are temporally cumulative and continue to evolve even after 70 years since its introduction. These impacts have led to dramatic reductions in prey availability, resulting in widespread cannibalism. Adult individuals preying on juveniles in areas with higher abundances of peacock bass indicated that cannibalism is size‐ and density‐dependent. Cannibalism was more frequent in non‐native populations and in human‐modified ecosystems. A complex feedback process (reproduce and cannibalise frequently) may be responsible for overcoming long‐term resource scarcity, and the cannibalism may not be a regulatory force strong enough to surpass the reproductive success of the population.Our findings at the local and continental scale converge to confirm the cannibalism as an adaptive invasiveness strategy that facilitates the invasion process and makes populations self‐sustainable in the long term, which may jeopardise the efficacy of management actions for these top predators introduced globally. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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3. Resource partitioning among freshwater congeneric fishes (Loricariidae: Hypostomus): trophic, spatial, and temporal dimensions.
- Author
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de Paiva Ferreira, Débora Lisandra, Guedes, Gustavo Henriques Soares, da Silva, Luana Giacoia, and Araújo, Francisco Gerson
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FRESHWATER fishes ,COEXISTENCE of species ,SPECIES distribution ,CATFISHES - Abstract
Resource partitioning is essential for coexistence of phylogenetically related species in altered environments, where changes in biotopes can limit resources and change ecological strategies. We investigated resource partitioning between two congeneric catfishes (Hypostomus affinis and H. luetkeni) in three niche dimensions (trophic, spatial, and temporal) in a Neotropical reservoir. We tested the hypothesis that the use of different mesohabitats (spatial dimension) is more relevant for the coexistence of species, and that morphological differences between the species confer different advantages in the mesohabitats occupation. We evaluated species morphology, diet composition and abundance along a spatial-temporal gradient. A high dietary overlap and a low temporal variability in species abundance were found, indicating that these two dimensions play a minor role in the species distribution. However, a strong spatial segregation modulated apparently by morphological differences was observed. Hypostomus luetkeni has a larger oral disk area, and a flatter body that confer advantages in the occupation of lotics habitats, whereas H. affinis has relatively larger fins that provide more efficient displacements in lentic habitats. Spatial partitioning was the main driver modulating mechanism for the coexistence of these species and differences in the occupation of the mesohabitats probably have been amplified in this altered environment. [ABSTRACT FROM AUTHOR]
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- 2023
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4. Can fish gill anomalies be used to assess water quality in freshwater Neotropical systems?
- Author
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Gomes, Iracema David, Nascimento, Aparecida A., Sales, Armando, and Araújo, Francisco Gerson
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- 2012
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5. Artificial flow regime promotes abiotic and biotic gradients: Testing the concept of longitudinal zonation in an off-river reservoir.
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Guedes, Gustavo Henrique Soares, Mattos, Tailan Moretti, Camilo, Geysa da Silva, Uehara, Wagner, Ferreira, Débora Lisandra de Paiva, and Araújo, Francisco Gerson
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BODIES of water ,FRESHWATER fishes ,FISH diversity ,GEOGRAPHICAL distribution of fishes ,SPECIES diversity ,RESERVOIRS - Abstract
Fragmentation and interconnection of water bodies cause severe changes in the natural flow regime of continental water systems. However, assessments of these impacts on the freshwater fish distribution are still scarce. We investigated whether an artificial flow regime generated by discharges from an aqueduct would promote a longitudinal environmental gradient in an off-river reservoir. We tested the hypothesis that the incoming water from aqueduct discharges promotes environmental gradient between lotic and lentic conditions. We expect that environmental changes and the artificial flow regime promote the structuring of fish assemblage and that the lotic-lentic transition areas present the highest fish species richness. A longitudinal gradient in environmental characteristics with differing fish assemblage structure was found. Temporal changes in the fish assemblages occurred only in areas near the discharge of the aqueduct. The highest fish richness and diversity were recorded in the transition zone during the wet season, associated with the greater environmental heterogeneity of this ecotone, whereas the lowest was found in the lotic zone, probably associated with the altered flow regime. The greatest abundance was recorded in the upper lentic zone in the wet season, whereas the lowest was found in the lower lentic zone in both seasons. Our results corroborate the hypothesis that the artificial flow regime, modulated by the seasonality of discharges and the influence of environmental variables, promotes longitudinal gradients in reservoirs when rivers are not present. The findings are relevant in a scenario where ever more interconnections of aquatic bodies have been diffused around the world. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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6. Influence of season, environment and feeding habits on the enzymatic activity of peptidase and β-glucosidase in the gastrointestinal tract of two Siluriformes fishes (Teleostei)
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Duarte, Silvana, Paiva, Marco A. R., Lara, Camila C., Bemquerer, Marcelo P., and Araújo, Francisco Gerson
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Enzymatic activity ,peptidases ,β-glucosidase ,physiology ,lcsh:Zoology ,reservoirs ,lcsh:QL1-991 ,fishes ,Siluriformes - Abstract
The enzymatic activities involved in the digestion of proteins and carbohydrates were compared among three organs of the digestive track of two Siluriformes fish species, and between two areas: a reservoir, and an area downriver of it. Our aim was to test the hypothesis that the digestive organs of species with varied feeding habits have different enzymatic activities, and that the enzymatic activity differs among seasons and environmental conditions. The iliophagous/herbivorous species Hypostomus auroguttatus Kner, 1854 had higher trypsin-like, chymotrypsin-like peptidase and β-glucosidase activity in the intestine when compared with the omnivorous species Pimelodus maculatus Lacepède, 1803, whereas the latter had more hepatic trypsin-like activity than the former. The peak of activity of the three enzymes in H. auroguttatus was recorded in the winter and spring. On the other hand, P. maculatus tended to have the more prominent peptidase and β-glucosidase activity in the summer, and the smallest in the winter. The intestine of H. auroguttatus had higher enzymatic (trypsin, chymotrypsin and β-glucosidase) activity than the stomach and the liver. For P. maculatus, the highest β-glucosidase activity was found in the liver. The enzymatic activity of H. aurogutattus did not differ between lotic and lentic systems, whereas P. maculatus had comparatively higher stomach and hepatic trypsin levels and hepatic chymotrypsin-like activities in the reservoir than down in the river. These findings indicate that, in H. auroguttatus, most digestive activity occurs in the intestine, which is long and adapted for the digestion of bottom-river vegetable matter and detritus. The seasons and the type of the system (lentic vs. lotic) seem to affect the enzymatic activity for these two species differently, a likely consequence of their different lifestyles.
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- 2013
7. Seasonal changes and spatial variation in the water quality of a eutrophic tropical reservoir determined by the inflowing river.
- Author
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Araújo, Francisco Gerson, Costa de Azevedo, Márcia Cristina, and Lima Ferreira, Maria das Neves
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SPATIAL variation ,WATER quality ,LAKES ,RESERVOIRS ,EUTROPHICATION ,WATERSHED management ,MANAGEMENT - Abstract
The water quality of a eutrophic tropical reservoir was studied over a 5-year period (2000–2004), with quarterly sampling (Jan, Apr, Jul, and Oct) carried out at 3 sampling stations with one station in each of 3 zones (fluvial, transitional, and lacustrine). During the wet season, large amounts of phosphorus were introduced into the reservoir by the increased inflow of the river. Dissolved oxygen, pH, and chlorophyll a levels peaked in the wet season; pH, chlorophyll a, and total phosphorus in several cases were recorded above the recommended Brazilian guidelines. Dissolved oxygen was lower than acceptable levels in the euphotic layer and reached very low levels in the hypolimnion, indicating thermal stratification. Efficient reservoir management is necessary to restore environmental quality, and our results indicate that selective withdrawal may be an effective means of improving the quality of water in Funil Reservoir. [ABSTRACT FROM PUBLISHER]
- Published
- 2011
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8. A preliminary fish assemblage index for a transitional river–reservoir system in southeastern Brazil
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Terra, Bianca de Freitas and Araújo, Francisco Gerson
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RESERVOIRS , *RIVERS , *BIOTIC communities , *AQUATIC animals , *ANIMAL classification , *WATER quality biological assessment , *CHARACIFORMES - Abstract
Abstract: Large river–reservoir systems are some of the most difficult aquatic ecosystems to assess because: (1) they typically lack minimally disturbed reference sites; (2) the reservoirs are not natural systems to begin with; and (3) reservoirs with high exchange rates are transitional systems between rivers and lakes. These features are further complicated in Brazil where fish species taxonomy is incomplete (let alone fully described ecologically), where waters naturally have high organic and thermal loadings, and where dams and reservoirs provide most of the nation''s electricity and water supplies. As a first step towards generating a biological tool for assessing the effects of reservoirs on rivers, we developed a preliminary River–Reservoir Fish Assemblage Index (RRFAI) in a transitional river–reservoir system in southeastern Brazil. To do so, we gill-netted fish monthly between October 2006 and September 2007 (excluding May and July 2007) immediately upriver of the reservoir, in the upper reservoir, in the lower reservoir, and immediately downriver of the reservoir. In developing our RRFAI we sought fish assemblage metrics to represent ecological characteristics including richness, habitat, trophic, tolerance, and resilience guilds. Despite clear differences in fish assemblage composition between river and reservoir sites, we found 9 metrics common to both systems that were nonredundant and had low sampling variability (number of native species, number of characiform species, number of siluriform species, % omnivorous individuals, % invertivorous individuals, % non-native carnivorous individuals, % intolerant individuals, % tolerant individuals, number of tolerant species). Fish assemblage condition was significantly and consistently lower in the lower reservoir. There was no significant difference between the dry and wet season in RRFAI scores, suggesting that a single season sample should usually suffice. Further research is needed along distinct disturbance gradients in multiple river–reservoir systems in Brazil to confirm the sensitivity of our preliminary RRFAI for assessing the physical and chemical habitat disturbances common to such systems. [Copyright &y& Elsevier]
- Published
- 2011
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9. Digestive tract morphology of the Neotropical piscivorous fish Cichla kelberi (Perciformes: Cichlidae) introduced into an oligotrophic Brazilian reservoir.
- Author
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Dos Santos, Alejandra Filippo Gonzalez Neves, Dos Santos, Luciano Neves, and Araújo, Francisco Gerson
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PISCIVOROUS fishes , *ALIMENTARY canal , *FISH morphology , *PERCIFORMES , *CICHLIDS , *RESERVOIRS - Abstract
Despite being one of the most well-known cichlid fish of importance to artisanal and sport fishing, and among the largest fishes in the Neotropics, data on digestive tract anatomy of peacock basses (Cichla spp.) are largely lacking, especially for non-native populations. In this paper, we describe for the first time the digestive tract morphology of Cichla kelberi, a voracious piscivore that was introduced in the 1950s into an oligotrophic and physically low-complex impoundment in Brazil. Peacock basses were collected between 1994 and 2002 in Lajes Reservoir, through gillnets (25 to 55mm mesh; 20-50x2m), seines (10x2.5m; 8.0mm mesh), cast nets and angling. All the fishes were kept on ice in the field and then transferred to the laboratory, where they were identified, measured, weighed and dissected for digestive tract analyses. The index of Relative importance-IRI was calculated for diet characterization while linear and non-linear regressions were performed to assess growth patterns of four morphological characters related to feeding (e.g. mouth width, mouth height, stomach length and intestine length) and the number of gill rakers during the C. kelberi ontogeny. Most digestive tract structures were directly related to the piscivorous diet of C. kelberi, indicating that peacock bass is a diurnal, bathypelagic and gape-size limited predator that feeds largely on shallow-water prey species within the littoral zone. Mouth width and height grew allometrically (b>1) with the size of peacock bass, broadening the size range in which prey can be eaten, but especially for predators smaller than ~400mm of total length. Differently, stomach and intestine lengths increased isometrically (b=1), which could constrain prey consumption for adult C. kelberi, especially those at advanced stages of gonadal maturation. The presence of longer-drawn, sharp and furcated gill rakers in C. kelberi may be related to increased prey retention in the resource-limited Lajes Reservoir, but further studies are necessary whether such features are randomly triggered by genetic or phenotypic anomalies, or effectively bring ecological advantages to the predator. In addition to contribute to improve the current biological knowledge on peacock basses, our results can be also useful to further comparisons on whether those morphological features related to feeding will change with transitions on prey consumption by C. kelberi and/or with the particular conditions of the invaded ecosystem. Rev. Biol. Trop. 59 (3): 1245-1255. Epub 2011 September 01. [ABSTRACT FROM AUTHOR]
- Published
- 2011
10. Size-related and seasonal changes in the diet of the non-native Cichla kelberi Kullander & Ferreira, 2006 in a lowland reservoir in the southeastern Brazil.
- Author
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Mendonça, Helaine Silva, Santos, Alexandre Clistenes Alcântara, Martins, Mariana Marques, and Araújo, Francisco Gerson
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CICHLA , *FISH feeds , *RESERVOIRS - Abstract
We examined size-related and seasonal changes in the diet of the peacock bass Cichla kelberi in a tropical lowland reservoir in southeastern Brazil over three hydro-climatic seasons: summer (high rainfall and temperature), winter (low rainfall and temperature), and late spring (increasing rainfall and temperature) during two years (2006-2007). The tested hypothesis is that this non-native predator fish changes diet during the subadult and adult phases and among seasons to adapt in new colonized environment. Fishes of the families Clupeidae (Platanichthys platana), Characidae (Astyanax spp.) and Cichlidae (Cichla kelberi) were the most important food items, followed by insects of the order Odonata. Cannibalism was also recorded for the largest individuals. A significant size-related change in diet was found with the smallest individuals (Total Length, TL < 20 cm) preying mainly on fishes, whereas the larger individuals (TL > 30 cm) preyed mainly on Odonata. The niche breadth increased during growth, with the largest individuals having a diet more evenly distributed among the available resources. No significant seasonal differences in diet composition were found, but stomachs with higher degree of volume occupied by food were more frequent in late spring than in summer. Conversely, the highest niche breadth was found during the summer compared to the other seasons. Together, these observations suggest an efficient use of the available resources by this top predator in this new colonized system. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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