Trophic Resource Partitioning Research Articles

Hydro-morphological features and functional structure of fish assemblages mediate species isotopic niches in estuaries

Despite the popularity of stable isotope analysis (Carbon and Nitrogen), the drivers of species isotopic niches and their consequences on food web functioning remained poorly described, especially in estuaries. Here, we hypothesised that species niche characteristics are influenced by ecosystem hydro-morphological features and the functional structure of fish assemblages. The trophic niches of four fish species (Dicentrarchus labrax, Pomatoschistus minutus, Sprattus and Platichthys flesus) and overlap between them were compared during two consecutive autumns in eight estuarine ecosystems of the northeast Atlantic Ocean. Our findings demonstrated a relative steadiness of trophic positions of fish in estuaries, despite a high level of interspecific variability. The seabass generally occupied the higher trophic position, followed by the sand goby, while the flounder and sprat were at the lowest position in the food web. Species isotopic niches and overlap were mediated by some estuarine features, including estuary size and intertidal extent, but also by biotic interactions at the intra- and inter-specific levels, as reflected by the influence of fish abundance and functional diversity metrics. Our results support the statement that the intertidal area is a pivotal factor in regulating trophic interactions, by promoting niche partitioning and diversification of trophic resources between species. Moreover, niche size and dietary divergence of species decreased with increasing regularity of trophic strategies within assemblages, suggesting that species occupied more restricted trophic niches when they were less subjected to competition for the same food resources. These findings emphasize the importance of local conditions and the functional composition of assemblages in modulating the trophic resources consumed by fish in estuarine environments.

Trophic ecology of small to large hylids from an Amazonia-Cerrado transitional zone in Brazil

The diet of an organism is related to its intrinsic characteristics, such as morphology, physiology, and behavior, and those of the prey it consumes. For species occurring in sympatry, the knowledge of the mechanisms that favor the co-occurrence of morphologically and ecologically similar species may be important to understand the resource partition in the assemblage. In this study, we analyze the diet of small to large hylids (i.e., Scinax fuscomarginatus, Dendropsophus anataliasiasi, Boana caiapo, and B. raniceps) in an Amazonia-Cerrado transitional zone, verifying if the diet of species with different body sizes is similar and if species diet is explained by the availability of prey in the environment. We found that the dietary patterns of the studied hylids were not driven by prey availability in the environment, with species feeding preys in an opportunistic way. In addition, the diet composition was similar among species, however, the volume of consumed prey varied according to the body size, with large species feeding more prey volume than the small ones. This pattern is predicted by the optimal foraging theory, in which larger predators tend to maximize their energy intake by consuming large prey. Altogether, the segregation depending on the body size can play a key role in trophic resource partitioning, with small species feeding small prey and larger species consuming small to large prey, but preferring the larger ones when there is an option, avoiding interspecific competition.

Probing for depth‐gradient diversification in the riverine‐spawning Dolly Varden: Insights from a recently discovered ecomorph assemblage

AbstractThe interplay of species could affect the pathways of adaptive diversification in lacustrine fishes. For instance, sockeye salmon is highly effective in transporting biomass from the ocean to the lakes providing abundant food supply for resident dwellers. The largest Asian population of sockeye salmon (>1.5 million spawners annually) reproduces in Lake Kurile (Russia). Here we investigate the possibility of the rapid in‐lake diversification of the tributary‐spawning charr (genusSalvelinus, Salmonidae) that colonised the Lake Kurile habitats >100 m depth and gained access to decomposing sockeye carcasses and eggs. The results confirm the trifurcation of the Lake Kurile charr along with the depth gradient into three reproductively isolated morphs: anadromous Dolly Varden utilising littoral and tributary resources, the resident slope charr and the profundal charr. No feeding specialisation among the morphs was found as the lake is rich in sockeye remains irrespective of depth. Thus, the in‐depth specialisation of the charrs did not result in the archetypical tropho‐morphological adaptations described for the majority of the deep‐water species of fishes. Only the size reduction and some paedomorphic peculiarities characterise the charr permanently dwelling in the 100–300 m depth zone. The lack of morphological differences among the morphs could be explained by the short period of evolutionary diversification. The divergence event is estimated to have occurred after the close of the glacial period in the middle of Holocene, which corresponds to the time of the lake formation. A bottleneck and subsequent rapid expansion can be traced in the demographic history of the profundal morph, suggesting the possibility of modern sympatric diversification in fish without a trophic resource partitioning.

Trophic Diversification Out of Ancestral Specialization: An Example from a Radiating African Cyprinid Fish (Genus Garra)

Trophic resource partitioning is one of the main ecological mechanisms of adaptive radiation. The Garra is a highly specialized periphyton feeder that has widened jaws equipped with a horny cutting scraper. In a river located in the Ethiopian Highlands in East Africa, a diversification of Garra composed of six sympatric ecomorphs which were strikingly diverse in trophic morphology was revealed. A hypothesis on trophic resource partitioning was tested using data on diet composition, gut length, and stable isotopes. The obtained results confirmed the trophic diversification of Garra ecomorphs. Three feeding modes were revealed: (i) periphytonophagy, (ii) mixed periphytonophagy and zoophagy, and (iii) zoophagy. The periphyton feeders had a long gut and were enriched in δ13C values compared to the shorter gut and lowered δ13C values in the zoophagous ecomorphs. Therefore, Garra could respecialize out of its ancestral specialization. This finding does not support the generalists-to-specialists hypothesis on the origin of specializations, and suggests that Liem’s paradox is a more common phenomenon. In the case of specialists, we assume that new ecological opportunities can be ‘visible’ to specialists if they are preceded by relaxed selection constrains that lead to the widening of the ecological/morphological plasticity to jump out of a canalized mode of ancestral specialization.

Trophic ecology of four species of emperor fish (Lethrinus) in the Gulf of Mannar along the Indian southeast coast

This study presents the trophic ecology and resource partitioning among four species of emperor fishes (Lethrinus lentjan, L.microdon, L. nebulosus and L.olivaceus) in the Gulf of Mannar, based on a year-round study conducted in 2019. All of them are demersal feeders with strong jaws, having certain differences in their body shape and dentition. The diet content analyses revealed that slow-moving benthic invertebrates such as molluscs, crustaceans, and echinoderms were the major diet components of L.lentjan and L. nebulosus, whereas, L.microdon and L.olivaceus predominantly consumed fast-moving prey that included nektons and other invertebrate taxa. The dominant prey components in the diet of smaller fishes are highly contrary to the adults, as larger fishes cover wider feeding grounds and choose among a broader category of prey, which is significant for greater nutritional input. The slender body shape, jaw structure, and foraging behaviour enable larger fish to consume a far greater proportion of nekton. The index of relative importance (IRI %) showed that bivalves, brachyurans, and carideans were the most prevalent food items in the diets of all size classes. TROPH values estimated by species and size groups indicate that L.microdon (3.71) occupies the highest trophic position, followed by L.olivaceus (3.68), L.lentjan (3.45), and L. nebulosus (3.37). The variety and frequency of prey components in L.microdon and L.olivaceus substantiate the distinctive feeding nature of piscivory with an ontogenic diet shift. The observed trophic partitioning among the four Lethrinus species in the Gulf of Mannar can be attributed to vertical habitat partitioning and their distinctive morphological characteristics.

Trophic Ecology and Resource Partitioning of Common Snook and Mexican Snook in the Usumacinta River Delta

AbstractCoexisting species often develop resource‐partitioning mechanisms to reduce their direct competition and optimize energy harvesting. Common Snook Centropomus undecimalis and Mexican Snook C. poeyi are carnivorous fish that coexist in estuaries of the Usumacinta River delta, in the southern Gulf of Mexico, and play an important role for fisheries and economy in this region. We analyzed spatial, temporal, and ontogenetic variability in trophic dynamics and distribution of Common and Mexican snooks. To identify patterns of trophic resource partitioning, we analyzed stomach content and stable isotopes (δ13C, δ15N) of the two species. Fifty‐one prey items were identified, with fish remains being the most abundant component (>35%). The two snook species appeared to be specialized carnivores of the third or fourth trophic level. Diet comparison indicated significant differences among species: Common Snook presented a higher proportion of fish from the families Engraulidae, Clupeidae, and Elopidae, while Mexican Snook consumed a higher fraction of fish from the families Cichlidae, Poeciliidae, and Loricariidae. The diet also presented significant variations between size‐classes. Small‐sized (<350 mm SL) Common Snook showed significantly higher reliance on invertebrates than large‐sized fish (>500 mm SL). Medium‐sized (351–499 mm SL) Mexican Snook consumed a higher proportion of Poeciliidae fish than small‐sized or large‐sized fish. The diet of the two snook species also presented important differences among seasons and sites. Trophic niche overlap between Common and Mexican snooks varied among systems, with higher overlap in the Pom−Atasta system than in the Palizada River. This study indicates that Common Snook and Mexican Snook have developed strategies for spatial partitioning of resources that favor their coexistence in the Usumacinta River delta.

Trophic ecology and resource partitioning of Haemulidae species along the Northeastern Brazilian continental shelf

Abstract In the Southeastern Tropical Atlantic, Haemulidae family play an important role both environmentally, acting as a link between lower and higher trophic levels, and socioeconomically, being widely caught by artisanal fleets. This study aimed to describe the trophic ecology of three grunt species (Haemulon aurolineatum, H. plumierii and H. squamipinna) considering spatial, temporal and ontogenetic aspects, integrating stomach content and stable isotopes analysis. Sampling occurred in 26 stations along the Northeast of Brazil (04°– 09°S), in August 2015 and April 2017, using bottom trawling net. There was greater feeding intensity at night, at latitudes below 08°S and in the inner continental shelf. Higher values of δ¹⁵N were reported for H. aurolineatum and H. plumierii collected near coastline. The isotopic niche breadth indicated that H. aurolineatum has a narrower diet thanH. plumierii. For the three species, the trophic level ranged between three and four. Considering stomach content and isotopic niche, diet was similar comparing species. This trophic ecology pattern reveals a likewise use of the habitat, which may be essential for identifying priority areas for conservation on an ecosystem basis, especially in rich reef zones that are subject to several increasing pressures, such as those in Northeast Brazil.

Annual precipitation predicts the phylogenetic signal in bat-fruit interaction networks across the Neotropics.

Closely related species tend to be more similar than randomly selected species from the same phylogenetic tree. This pattern, known as a phylogenetic signal, has been extensively studied for intrinsic (e.g. morphology), as well as extrinsic (e.g. climatic preferences), properties but less so for ecological interactions. Phylogenetic signals of species interactions (i.e. resource use) can vary across time and space, but the causes behind such variations across broader spatial extents remain elusive. Here, we evaluated how current and historical climates influence phylogenetic signals of bat-fruit interaction networks across the Neotropics. We performed a model selection relating the phylogenetic signals of each trophic level (bats and plants) with a set of current and historical climatic factors deemed ecologically important in shaping biotic interactions. Bat and plant phylogenetic signals in bat-fruit interaction networks varied little with climatic factors, although bat phylogenetic signals positively covaried with annual precipitation. These findings indicated that water availability could increase resource availability, favouring higher niche partitioning of trophic resources among bat species and hence bat phylogenetic signals across bat-fruit interaction networks. Overall, our study advances our understanding of the spatial dynamics of bat-fruit interactions by highlighting the association of current climatic factors with phylogenetic patterns of biotic interactions.

Fine-scale coexistence between Mediterranean mesocarnivores is mediated by spatial, temporal, and trophic resource partitioning.

The partition of the ecological niche can enhance the coexistence of predators due to differences in how they exploit three main resources: food, space, and time, the latter being an axis that often remains unexplored.We studied niche segregation in a Mediterranean mesocarnivore community composed by Vulpes vulpes, Genetta genetta, Meles meles, and Herpestes ichneumon, addressing simultaneously different niche axes: the temporal, trophic, and spatial axes.We assessed temporal segregation between mesopredators and prey and between potential competitors, using camera trap data between 2018 and 2020 in a Mediterranean landscape in Southern Spain. We deployed camera traps in 35 stations in three sites with varying vegetation cover within Doñana National Park. We further examined the spatial overlap in activity centers and trophic preferences between potential competitors using diet information from studies performed in the study area.We found an overall temporal segregation between trophic generalist species, with species showing higher temporal overlap differing in their trophic preferences and/or showing limited spatial overlap. Furthermore, we observed an overall high overlap between the activity patterns of predators and their major prey in the area (the common genet vs. small mammals and the red fox vs. European rabbit).Our study suggests that coexistence of the different species that compose the mesocarnivore assemblage in Mediterranean landscapes can be facilitated by subtle differences along the three main niche axes, with temporal segregation being a most pronounced mechanism. Our findings reinforce the idea that the coexistence mechanisms underlying community structure are multidimensional.

Trophic resource partitioning among four sympatric lutjanid species in the southern Mexican Caribbean Sea

ABSTRACT Snappers are marine fishes that inhabit reef ecosystems and have a wide distribution throughout tropical and subtropical waters of the Atlantic, Indian and Pacific Oceans. These species are resources of economic importance, there is a lack of biological and ecological knowledge about these species in the studied area, and their meat is highly valued for human consumption. To contribute to the ecological knowledge, this work reports on the feeding habits of four species of snapper: Lutjanus synagris, Lutjanus griseus, Lutjanus analis and Lutjanus apodus, through the identification of stomach contents and a similarity analysis for the diets. Results showed that the most important prey items were crustaceans. Differences were found in the consumption of specific prey: Portunus were mainly consumed by L. griseus; Cronius was consumed by L. apodus; and Pitho was consumed by L. analis and L. synagris. Identification of prey species to genus and species levels allowed the characterization of the feeding habits of these sympatric species and highlighted the need for research programmes focused on crustaceans that guarantee their availability and abundance in the ecosystem.

Unexpected Diversity of Feeding Modes among Chisel-Mouthed Ethiopian Labeobarbus (Cyprinidae)

Trophic resource partitioning is one of the main drivers of adaptive radiation. The evolutionary diversification of large African barbs, the genus Labeobarbus, seems to be related to mouth polymorphism. The chisel-mouthed or scraping phenotype has repeatedly evolved within Labeobarbus. At least five ecomorphs with a scraping mouth morphology were detected in the waters of the Ethiopian Highlands and can be provisionally classified into two groups: (i) “Varicorhinus”-like, and (ii) “Smiling”-like. Previously, all Labeobarbus with a scraping-mouth morphology were considered to be periphyton feeders. Using data on morphology, diet and stable isotope ratios (C and N), we addressed the question: does a scraping-mouth morphology predict feeding on periphyton? Our study revealed that five scraper ecomorphs exhibited three main feeding modes: (i) periphyton-eating, (ii) herbivory–detritivory, and (iii) insectivory. Two cases of the parallel divergence of sympatric ecomorphs with distinct feeding modes (herbivory–detritivory vs. insectivory) were revealed in two geographically isolated basins. A significant difference in δ15N values was detected among sympatric scraper ecomorphs. A periphytonophagous scraper was rich in δ15N values that are comparable with those in sympatric piscivorous fish. This data sheds light on the possibility of the utilization of periphyton as a protein-rich food by fishes.

Vector of Trophic Resource Partitioning in the Variability of Individuals of the Generalized form of the Large African Barbs of the Barbus (= Labeobarbus) Intermedius Complex, Ethiopia, Tana, Langano and Awasa Lakes

Analysis of the diversification of barbs of the generalized form of the Barbus (= Labeobarbus) intermedius complex in the monomorphic populations of Langano and Awasa lakes and in the polymorphic population of Lake Tana makes it possible to reveal parameters of the variability that is directed to trophic resource partitioning. The great similarity of the parameters revealed in the three studied water bodies shows that in monomorphic populations the structure of variability directed to trophic resource partitioning is identical to that in the polymorphic population. The concept of “vector of trophic resource partitioning” is introduced. In the polymorphic population, this vector makes the main contribution to the diversification of individuals, while its importance is secondary in monomorphic populations. It is concluded that the different evolutionary potential of polymorphic and monomorphic populations is determined by the specific weight of diversification caused by the vector of trophic resource partitioning. The original method of data analysis used in the study may be promising for studying similar situations in other systematic groups.

Trophic ecology of syntopic anurans of tropical stream communities

AbstractWe investigated trophic resource partitioning in seven syntopic anurans from low- and mid-elevation stream habitats of a tropical riparian ecosystem by utilising stomach content analysis (SCA) and stable isotope analysis (SIA). Our SCA data revealed dietary similarities, narrow trophic niche breadth, and low dietary niche overlap inAnsonia muelleri, Limnonectes magnus, Occidozyga laevis, Megophrys stejnegeri, Pulchrana grandocula, Sanguirana mearnsi, andStaurois natatorwhich could be attributed to these anurans’ selection of available local prey items. We confirmed ant-specialisation (myrmecophagy) of the Mindanao island endemic bufonidA. muelleribased on our temporal SCA dietary data. Our SIA estimates of assimilation of potential prey sources confirmed thatL. magnus,P. grandocula, andO. laevisare generalist predators, opportunistically feeding on locally abundant insect prey items. This study on trophic resource partitioning in syntopic anurans provides the first picture of trophic interactions, i.e., predation and competition in stream communities in tropical riparian zones of a watershed ecosystem in northeast Mindanao of the southern Philippines.

The effects of morphology, phylogeny and prey availability on trophic resource partitioning in an anuran community

Several factors influence the partitioning of trophic resources in ecological communities, such as morphology, evolutionary history, and resource availability. Although the effects of morphology, phylogeny, and resource availability on trophic ecology have long been explored by theoretical studies, little has been done to empirically test these relationships. Here, we tested whether phylogenetic and morphological distances correlate with trophic niche overlap using a path analysis of multiple partial regression of distance matrices. Also, we tested whether niche breadth is influenced by body size using Phylogenetic Generalized Least Squares analysis. Trophic niche overlap was better explained by morphology per se than by the phylogenetic distance. We also found that predator's body size influences niche breadth calculated considering prey traits and availability, but not when we do not include these availability data. Additionally, trophic niche breadth was usually smaller when we considered prey traits and availability, differently from niche overlap, whose values increased when we did not consider these data. Our findings show that the interpretation of trophic niche in communities changes if we consider availability data, affecting inferences about coexistence and trophic specialization. Our study contributes to understanding trophic specialization and emphasizes the importance of incorporating prey availability and their traits into diet analysis.

Isotopic niche partitioning between two small cetacean species

Commerson’s dolphin Cephalorhynchus commersonii and Peale’s dolphin Lagenorhynchus australis live in sympatry along the southwestern South Atlantic Ocean, suggesting the existence of some degree of habitat partitioning to reduce their competition for resources. Both species are usually associated with coastal environments, but information on their trophic ecology is scarce. Here we explored the existence of trophic resource partitioning between these 2 sympatric species using δ13C and δ15N. From 2007 to 2013, we analyzed a total of 14 Commerson’s dolphin and 34 Peale’s dolphin skin samples from a marine protected area in Argentina. Significant differences in δ13C values indicated intra- and interspecific spatial partitioning. Three different Peale’s dolphin feeding groups (FGs) were identified: FG1 exclusively exploited the pelagic habitat, FG2 occupied more pelagic/inshore habitats (similar to Commerson’s dolphins), and FG3 occupied more benthic/inshore habitats. Isotopic niche breadth varied between species and feeding groups, exhibiting less variation in prey selection among Commerson’s dolphins. According to Bayesian standard ellipse area analysis, isotopic niche overlap was found between FG2 and FG3 from 2007 to 2012, and between FG2 and Commerson’s dolphins. Mixing models suggest that FG3 has a diet mainly based in benthic fish, while FG2 and Commerson’s dolphins feed predominantly on pelagic fish. Overall, this study indicates segregation in the use of trophic resources between 2 sympatric dolphin species, showing different foraging strategies that promote coexistence and reduce intra- and interspecific competition. Furthermore, the presence of 3 Peale’s dolphin feeding groups segregated at a small geographic scale suggests a previously unknown ecological complexity.

Trophic resource partitioning drives fine-scale coexistence in cryptic bat species.

Understanding the processes that enable species coexistence has important implications for assessing how ecological systems will respond to global change. Morphology and functional similarity increase the potential for competition, and therefore, co‐occurring morphologically similar but genetically unique species are a good model system for testing coexistence mechanisms. We used DNA metabarcoding and high‐throughput sequencing to characterize for the first time the trophic ecology of two recently described cryptic bat species with parapatric ranges, Myotis escalerai and Myotis crypticus. We collected fecal samples from allopatric and sympatric regions and from syntopic and allotopic locations within the sympatric region to describe the diets both taxonomically and functionally and compare prey consumption with prey availability. The two bat species had highly similar diets characterized by high arthropod diversity, particularly Lepidoptera, Diptera and Araneae, and a high proportion of prey that is not volant at night, which points to extensive use of gleaning. Diet overlap at the prey item level was lower in syntopic populations, supporting trophic shift under fine‐scale co‐occurrence. Furthermore, the diet of M. escalerai had a marginally lower proportion of not nocturnally volant prey in syntopic populations, suggesting that the shift in diet may be driven by a change in foraging mode. Our findings suggest that fine‐scale coexistence mechanisms can have implications for maintaining broad‐scale diversity patterns. This study highlights the importance of including both allopatric and sympatric populations and choosing meaningful spatial scales for detecting ecological patterns. We conclude that a combination of high taxonomic resolution with a functional approach helps identify patterns of niche shift.

Trophic resource partitioning by sympatric ecomorphs of Schizopygopsis (Cyprinidae) in a young Pamir Mountain lake: preliminary results

Four sympatric ecomorphs – detritivorous, predator, benthivorous, and phytophagous – of the cyprinid fish Schizopygopsis stolickai were recorded in a young Pamir lake, Lake Yashilkul, located at > 3,700 m above sea level. Some ecomorphs are divergent in diet, gut length, and stable isotopes of δ13C and δ15N. The predator ecomorph has a shorter gut, and is the most enriched in δ15N (14.5‰), indicating its occupation of the highest trophic level. The lowest δ15N values (11.1‰) were detected in the detritivorous ecomorph. There was significant overlap in the diet of some individuals belonging to different ecomorphs, reflecting high trophic plasticity despite ongoing trophic specialization.

Fishing alters resource partitioning between colour morphs in a temperate coastal fish

Resource partitioning in polymorphic fish species is expected to be altered by human exploitation, as individual specialization is density dependent in many vertebrates. We tested this hypothesis using the ballan wrasseLabrus bergyltaas a model species. We compared the isotope niches of the plain and spotted morphs of the species in a marine protected area (MPA) and in adjoining areas open to fishing, both off Galicia (NW Spain). Underwater visual census confirmed a 3-fold increase in the biomass of ballan wrasse off the Cíes Islands compared to areas open to recreational fishing, thus demonstrating that populations outside MPAs are well below carrying capacity. The stable isotope ratio of C revealed differences in the resource use patterns of plain and spotted ballan wrasses both in areas open and closed to fishing, as plain wrasses were always depleted in13C compared to sympatric spotted ones. The stable isotope ratio of N showed that plain ballan wrasses foraged consistently at a higher trophic level than spotted ones in areas of high population density closed to recreational fishing, whereas differences did not exist or were reversed in areas open to fishing. These results demonstrate that the pattern of trophic resource partitioning between 2 morphs of the ballan wrasse is density dependent and that plain and spotted ballan wrasses likely had different ecological niches in pristine ecosystems.

Resource partitioning among stranded aquatic mammals from Amazon and Northeastern coast of Brazil revealed through Carbon and Nitrogen Stable Isotopes

Aquatic mammals play an important role in community structure. The present study applied stable isotope analysis (SIA) to evidence trophic relationships and resource partitioning among aquatic mammals inhabiting different environments in the Amazon estuarine complex and adjacent coastal zone (AE) and Northeastern coast (NC) of Brazil. In addition, isotopic niche partitioning among Sotalia guianensis, Inia spp. and Trichechus inunguis within the AE was also evaluated, and ecological S. guianensis stocks were characterized. Among marine delphinids, the carbon isotopic composition in offshore species mirrored that of nearshore species, contradicting the pattern of decreasing δ13C values characteristic of many areas around the world including areas in Southeastern and Southern Brazil. Isotopic niches were highly distinct, with no overlap among the assessed species inhabiting the AE. Inia spp. and T. inunguis occupied significantly larger isotopic niche spaces, suggesting high habitat plasticity. S. guianensis inhabited two coastal regions indicating an ecological distinction. Nitrogen values were similar between S. guianensis from the NC and AE, indicating comparable trophic positions. However, NC specimens presented more variable δ13C values compared to those from AE. SIA results also allowed for insights concerning habitat use and the trophic ecology of dolphin species inhabiting different oceanographic regions off Northern/Northeast Brazil. These findings provide novel data on the stable isotope composition for cetaceans and sirenians from this region, and aid in furthering knowledge on the trophic ecology and habitat use of the investigated species.

Trophic morphology features allow Astyanax endemic species coexistence in a Neotropical river system.

Resource partitioning has an essential role in interspecific relations, especially in congener species, which share many morphological traits. In some places, small characids coexist through resource partitioning, which may reduce their interspecific competition. Astyanax species (e.g., Astyanax minor, Astyanax gymnodontus and Astyanax bifasciatus), for example, coexist in different water bodies from the Iguaçu River basin. These species have high phenotypic plasticity and many morphologic specializations that allow them to live in different habitats. Based on evidences that these species modified their feeding habits because of changes in resource availability in Iguaçu River, this study tested two hypotheses: (a) there are differences in head morphology, number of teeth and number of gill rakers among the species of Astyanax; and (b) there are differences in gill arch and gill raker morphology among the species of Astyanax, which may favour their trophic resource partitioning in Iguaçu River. The head morphological traits and quantitative morphological characters were summarized in a principal coordinates analysis (PCoA), and the analysis of similarities (ANOSIM) showed significant differences among species. Gill morphological measurements were analysed through analysis of covariance (ANCOVA), and it also showed significant differences in gill arch and gill raker morphology among species. Therefore, the analysis of ecomorphological traits related to trophic habits revealed some differences that may suggest a tendency of reducing competition for trophic resources in the Iguaçu River basin.