Made available in DSpace on 2016-08-17T15:00:42Z (GMT). No. of bitstreams: 1 Gildevan Nolasco Lopes.pdf: 963789 bytes, checksum: d73e668c2731927697f98bf14d6ea427 (MD5) Previous issue date: 2009-03-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study compared the morphological variation among different populations of Cnemidophorus ocellifer in areas of restinga, and investigated the pattern of sexual dimorphism for this species in this region. Therefore, 130 specimens were collected from four independent areas of restinga in Maranhão Island (Panaquatira, Raposa, Araçagy, and São Marcos Beaches), and measured in the laboratory. Significant morphological differences occurred both for populations and sexes. The populations differed in both body size and shape. The lizards from Raposa showed larger sizes. And the lizards from Panaquatira had more morphological variation, showing shorter limbs and longer trunks. The males of C. ocellifer showed larger body and head, while females had more elongation of the body. The morphological differences were attributed to ecological processes suffered by different groups. / Este estudo comparou a variação morfológica entre populações de Cnemidophorus ocellifer presentes em áreas de restinga, e investigou o padrão de dimorfismo sexual para esta espécie nesta região. Para isso foram coletados 130 espécimes em quatro áreas independentes de restinga na Ilha do Maranhão (Praias de Panaquatira, Raposa, Araçagy e São Marcos) e mensurados em laboratório. Diferenças morfológicas significantes ocorreram tanto para as populações quanto para os sexos. As populações divergiram tanto no tamanho do corpo quanto na forma. Os lagartos da Raposa apresentaram maiores tamanhos. E os lagartos de Panaquatira tiveram maior variação morfológica, apresentando menor comprimento dos membros locomotores e maior alongamento do meio do corpo. Os machos de C. ocellifer apresentaram maior tamanho do corpo e da cabeça, enquanto que as fêmeas apresentaram maior alongamento do corpo. As divergências morfológicas encontradas foram atribuídas a processos ecológicos diferenciados sofridos pelos grupos.

Orientador: Prof. Dr. Charles Morphy D. Santos / Coorientadora: Profa. Dra. Mirian Liza Alves Foranceli Pacheco / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Evolução e Diversidade, Santo André, 2018. / A presente tese teve por objetivo contribuir para o conhecimento a respeito da megafauna do Cenozóico do continente Americano. O foco do trabalho foi o estudo da megafauna pleistocênica da América do Sul, para correlações paleobiogeográficas e paleoecológicas, e da superordem Xenarthra, para considerações sobre ecomorfologia. Para as análises ecomorfológicas, foi considerado um contexto geocronológico e geográfico mais amplo, incluindo nas análises espécimes tanto do Neógeno quanto do Quaternário da América do Sul e do Norte. Foram descritas novas ocorrências de fósseis de mamíferos de grande porte ¿ tais como preguiças gigantes, gliptodontes, gonfotérios, tigres-dente-de-sabre e ursídeos ¿ para o estado do Mato Grosso do Sul. As considerações paleobiogeográficas consitiram em uma tentativa de correlação da paleofauna do Pleistoceno da Serra da Bodoquena com outras regiões da América do Sul. Além disso, uma nova ocorrência de filhote fossilizado de Nothrotherium maquinense é reportada para o estado de São Paulo com posterior datação radiométrica e análise de isótopos de carbono. O segundo ponto abordado nesta tese incluiu estudos ecomorfológicos em Xenarthra fósseis e atuais com base no formato do úmero. Para este fim, foi aplicado o método de morfometria geométrica bidimensional e tridimensional. Os resultados obtidos mostram que a Serra da Bodoquena apresenta maior similaridade taxonômica com a Região Intertropical Brasileira, devendo, portanto, ser incluída neste contexto paleobiogeográfico. Também verificou-se a ocorrência de um segundo táxon de Nothrotheriinae e de Ursidae em território brasileiro, além de um terceiro táxon de Scelidotheriinae. Os resultados sobre N. maquinense no estado de São Paulo indicam que a espécie estava presente na região por volta dos 13 mil anos antes do presente, e que se alimentava de plantas C3, indicando a possibilidade da presença de ambientes mais úmidos na região. Do ponto de visto ecomorfológico, foi verificado que o úmero de Xenarthra é funcionalmente informativo, sendo possível distinguir indivíduos adaptados para modos de vida arborícolas, semiarborícolas, ambulatoriais e escavadores. Adicionalmente, foi contastado a influência do tamanho sobre o formato do úmero. / The present thesis aimed to contribute to the knowledge about the Cenozoic Megafauna from the American continent. The focus was on both the Pleistocene Megafauna from South America, regarding paleobiogeographical correlations, and on the superorder Xenarthra, regarding considerations on ecomorphology. A broader geochronological and geographic context was considered to the ecomorphological analyses, including both Neogene and Quaternary specimens from South America and North America. The paleobiogeographical considerations were an attempt to correlate the Pleistocene paleofauna from Serra da Bodoquena to other South American regions. In addition, new occurrences of large mammal fossils ¿ such as giant sloths, glyptodonts, gomphotheres, felines and ursines ¿ were described for the state of the Mato Grosso do Sul. Additionally, a new occurrence of fossil cub identified as Nothrotherium maquinense was reported to the state of São Paulo. Dating and stable isotopes analyses were conduced. The second point addressed in this thesis includes ecomorphological studies on extant and extinct Xenarthrans based on the humerus shape. For this purpose, the bidimensional and tridimensional geometric morphometrics method were applied. The results showed that the Serra da Bodoquena presents greater taxonomic similarity to Brazilian Intertropical Region. Therefore, Mato Grosso do Sul should be included in this paleobiogeographical context. Additionally, the occurrence of a second Nothrotheriinae and Ursidae taxa, and a third Scelidotheriinae taxa was reported to Brazilian territory. The results on N. maquinense point out that such species was present in the region around 13 kya and it fed on C3 plants. This fact indicates the possibility of the presence of wetter environments in that region during late Pleistocene. From the ecomorphological point of view, it was verified that the Xenarthra humerus is functionally informative, being possible to distinguish individuals adapted to arboreal, semiarboreal, ambulatory and digger habitus. The influence of size on the humerus shape has been verified as well.

A ecomorfologia apresenta diferentes ramos, sendo a ecomorfologia comparada o ramo proposto neste trabalho, qual segue a análise das estruturas convergentes dos representantes das famílias africana Pantodontidae e neotropical Gasteropelecidae. Para tal, são analisadas e discutidas as pressões seletivas exercidas pelos ambientes muito similares encontrados nos pequenos córregos e igarapés localizados no interior da Floresta do Congo e Floresta Amazônica, onde vivem respectivamente as espécies africanas e neotropicais. Assim, foi possível identificar uma forte convergência adaptativa na musculatura das nadadeiras peitorais, uma vez que são adaptações aos saltos de longo alcance para fora dágua, característicos de todas as espécies analisadas, tratadas em conjunto por peixes-borboleta de água doce (Weist, 1995; Saidel et al., 2003). / The ecomorphology studies present different fields. The Comparative Ecomorphology, the field suggested at this work, follows the analyses of convergent structures found among Pantodontidae african families and Gasteropelecidae neotropical families. Due to that, we evaluated the selective pressures from similar aquatic environments, such as streams and small rivers. The analyses of african and neotropical species were done in relation to the Congo and Amazon Forest areas, respectively. In this context, we identified strong adaptive convergence in the musculature associated to the pectoral fins. These adaptations are related, in both studied cases, to the ability to jump long distandes out of the water (Weist, 1995; Saidel et al., 2003).

No description available.

This research tested the ability of fish morphology to predict membership of fishes in habitat guilds, their swimming performance, and habitat preference. Further, it considered methods for choosing a surrogate species to identify habitat of target species. Morphological discriminant functions were developed using morphological traits of fishes from one river to identify membership in two habitat guild systems (mesohabitat and microhabitat). Functions were then used to test factors influencing classification success of holdout tests and validated using fishes of a second river. Morphology was only partly successful (50%) at predicting membership in habitat guilds. Morphology identified species by shape, i.e., classifying test species into guilds with members of their genus, but not habitat use, because morphology and habitat were not strongly linked through function. By improving guild definition, relationships between morphology and habitat (Froude number) were identified for all fish groups examined (darters, benthic minnows, pelagic minnows, and suckers). Relationships were not transferable among groups. Further, morphology of eight minnows was linked to swimming performance, a key task for using habitat, in lab measurements of critical swimming speeds. In turn, swimming performance was related to habitat (Froude number). Morphology will be most successful at predicting habitat use of fishes when (1) more, discrete guilds are used, (2) guilds are identified within families, (3) variation in lifestyles (benthic vs. pelagic) is considered, and (4) key tasks related to using habitat are strongly associated with morphology. Finally, I examined a phylogenetic approach to identifying useable habitat. Closely related surrogate species were not more accurate in identifying habitat of target species than surrogates chosen by other methods. When a target species used only one mesohabitat, the highest overlap in habitat use occurred with other fishes of the same family using that mesohabitat (within a physiographic province). For target species using several mesohabitat types, surrogates from the next highest taxonomic unit, e.g., genus or subgenus, provided the most accurate information. Ecomorphology offers a mechanistic and defensible method for identifying habitat preferences of fishes and should be more widely considered as a tool for establishing habitat relationships of stream fishes. / Ph. D.

Anfíbios anuros representam um grupo de vertebrados cujo plano corpóreo apresenta uma série de modificações associadas ao desempenho locomotor através de saltos, sendo estas especializações muito antigas e conservadas filogeneticamente. Embora estudos comparativos venham demonstrando associações entre desempenho de salto e diversidade de habitat e história de vida para esse grupo filogenético, as relações entre o desempenho locomotor e o comportamento antipredatório dentro do contexto da diversificação do uso do micro-habitat permanecem inexploradas. Primeiramente, nós testamos modelos adaptativos de evolução morfológica associados com a diversidade do uso do micro-habitat (aquático, arborícola, fossorial, reofílico e terrestre) em espécies de anuros e foi examinada a relação da distância máxima do salto como uma função dos componentes das variáveis morfológicas e do uso do micro-habitat. Nós também investigamos, tanto em nível intra quanto interespecífico a influência da complexidade do microambiente (arena vazia, arena com folhiços ou arena com folhiço e arbustos) e do tipo de estímulo (aproximação versus toque) na manifestação do comportamento antipredatório em anuros. Adicionalmente, nós investigamos o efeito do uso de diferentes tipos de refúgio pelos anuros quando sujeitos aos testes de simulação predatória no laboratório. Nossos resultados demostram a existência de múltiplos ótimos adaptativos para os comprimentos dos membros associados aos diferentes usos do micro-habitat, com uma tendência de aumento dos membros posteriores em espécies reofílicas, arborícolas e aquáticas quando comparadas com espécies terrestres e fossoriais, as quais evoluíram em direção ao ótimo adaptativo com membros posteriores mais curtos. Além disso, espécies reofílicas, arborícolas e aquáticas apresentaram maior desempenho para o salto e membros posteriores mais longos quando comparadas com espécies terrestres e fossoriais. Em seguida foi abordada a influencia da complexidade do ambiente no comportamento antipredatório e nossas análises intraspecíficas mostraram que o número de respostas ativas (salto) e passivas é fortemente dependente do tipo de estímulo e varia de acordo com a complexidade estrutural do ambiente. Simultaneamente, nossas análises comparativas interespecíficas mostraram que anuros modulam a distância saltada em resposta ao toque do predador de acordo com a complexidade ambiental, e nós ressaltamos uma variação interespecífica associada ao uso de micro-habitat. Por fim, foi investigado o uso de refúgios pelos anuros expostos a testes de simulação predatória. Nossos resultados mostram que os anuros usam a vegetação arbustiva, o folhiço e a água como areas de refúgio quando sujeitadas a simulação predatória. Além disso, ocorreu variação interespecífica na escolha de refúgios potencialmente associados à diversificação do uso de microhábitat / Anuran amphibians represent a group of vertebrates whose body plan presents a series of changes associated with jumping locomotor performance; these specializations are very old and phylogenetically conserved. Although comparative studies have shown associations among jumping performance, habitat diversity and life history for this phylogenetic group, the relationship between locomotor performance and antipredator behavior remains unexplored within the context of diversification of microhabitat use and habitat. First, we tested adaptive models of morphological evolution associated with the diversity of microhabitat use (aquatic, arboreal, fossorial, torrent and terrestrial) in species of anurans and examined the relation of the maximum distance jumped as a function of components of morphological variables and microhabitat use. We also investigated, both at intra and interspecific levels, the influence of the complexity of microenvironment (empty arena, with leaf litter or bushes) and stimulus type (approach versus touch) on the manifestation of antipredator behavior in anurans. In addition, we investigated the effect of the use of different types of refuges by anurans when subjected to simulated predator tests in the laboratory. Our results demonstrate the existence of multiple optima of limb lengths associated to different microhabitats, with a trend of increasing hindlimbs in torrent, arboreal, aquatic species whereas fossorial and terrestrial species evolve toward optima with shorter hindlimbs. Moreover, arboreal, aquatic and torrent anurans have higher jumping performance and longer hindlimbs, when compared to terrestrial and fossorial species. Then, was addressed the influence of the complexity of environment on antipredator behavior and our intraspecific analyzes showed that the number of active responses (jump) and passive responses is strongly dependent on stimulus type and varies according to the structural complexity of the environment. At the same time, our interspecific comparative analyzes showed that anurans modulate the distance jumped in response to the predator\'s touch according to environmental complexity, and we highlight an interspecific variation associated with the use of microhabitat. Lastly, was investigated the use of refuges by anurans exposed to simulated predation events. Our results show that anurans use bushes, leaf litter and water as refuge areas when subjected to simulated predator. Moreover, there is interspecific variation in the choice of refuges potentially associated to diversification of microhabitat use

Made available in DSpace on 2017-07-10T14:38:34Z (GMT). No. of bitstreams: 1 Liege.pdf: 1528273 bytes, checksum: 24802d187b49fbdd9ae41bc256da6f08 (MD5) Previous issue date: 2012-08-24 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Predict how biological characteristics of the species fit the peculiarities of habitats is a key issue in ecology. Morphology assists in understanding this process, which is important for evaluating the effects of the habitat disturbances in the aquatic community, while reservoirs are complex ecosystems with ideal spatial gradients to examine the habitat s effect on species distribution. Thus, the hypothesis evaluated is that the species which share similar characteristics to form groups occupy similar habitats. Samples of fish were performed in longitudinal and transverse gradients for 3 years and selected 14-18 adults of each species were selected for morphometry. Mantel s and Partial Mantel s Tests identified relationships between spatial distribution, ecomorphological index and the phylogenetic distances. By non-metric multidimensional scaling and permutational multivariate analysis of variance it was identified that both, longitudinal and transversal gradients, had influence on species distribution, but the transversal gradient was the most influential on the abundance of species. From common species, according to Indicator Species Analysis (INDVAL), six were indicators of the littoral zone, three were indicators of deep zone, and two were indicators of the pelagic zone end four species occurred in more than one. Canonical Discriminate analysis was used to identify ecomorphological index that contributed to groups of species formed at INDVAL. Index related to head and mouth separate the species of the deep zone from littoral and pelagic ones, while body form and eye separated the pelagic from littoral zone. The morphology helped to define groups of species according to transversal gradient. The littoral zone had the greatest number of indicator species and greater morphological diversity than the pelagic and deep zones of Salto Santiago Reservoir, representing the importance of this habitat for species. Among the pelagic zone and deep, the morphology of the species is more specialized in locomotion and foraging, demonstrating the close relationship between habitat and morphology / Prever como características biológicas das espécies se ajustam às peculiaridades dos habitats é uma questão-chave na Ecologia. A morfologia auxilia na compreensão desse processo, o qual é importante para avaliar os efeitos das perturbações do habitat sobre as comunidades aquáticas, enquanto que reservatórios são ecossistemas complexos que formam gradientes espaciais ideais para inferir efeitos de habitats na distribuição das espécies. Deste modo, a hipótese testada foi que espécies que partilham características similares formam grupos que ocupam habitats semelhantes dentro do reservatório. Amostragens de peixes foram realizadas nos gradientes longitudinal e transversal durante três anos e selecionados de 14 a 18 adultos de cada espécie para morfometria. Os testes de Mantel e Mantel parcial identificaram interdependências entre distribuição espacial, índices ecomorfológicos e filogenia das espécies. Através da técnica de escalonamento multidimensional não-métrico e da análise multivariada de variância permutacional foi identificado que ambos os gradientes longitudinal e transversal influenciaram na distribuição das espécies, porém o gradiente transversal foi o mais influente. Das espécies mais abundantes, a Análise de Espécies Indicadoras (INDVAL) identificou 6 espécies com preferência à zona litorânea; três à zona profunda; duas à zona pelágica e 4 espécies ocorreram em mais de uma zona. A Análise de Discriminante Canônico foi utilizada para identificar os índices ecomorfológicos que mais contribuem para distinção entre os grupos de espécies indicadoras formadas na INDVAL. Índices relacionados à cabeça e boca separam espécies da zona profunda das zonas litorânea e pelágica, enquanto forma do corpo e olho separou espécies da zona pelágica da litorânea. Assim, a morfologia contribuiu para a formação dos grupos de espécies de acordo com o gradiente transversal. A zona litorânea apresentou maior número de espécies indicadoras e maior diversidade morfológica que as zonas pelágica e profunda do reservatório de Salto Santiago, indicando a importância desse habitat para as espécies. Entre as zonas pelágica e profunda, a morfologia das espécies foi mais especializada na locomoção e forrageio, demonstrando a intima relação entre habitat e morfologia

<p>In this thesis, the shape of the distal humerus trochlea is analysed using landmark-based morphometrics and multivariate methods, with the aim of exploring locomotor evolution in carnivorans. Elbow joint morphology is used together with body size and craniodental morphology to characterize past and present carnivorans. Evolutionary implications are studied at the ordinal, familial, and species levels, testing specific hypotheses about scaling, morphological constraints, evolutionary trajectories, and potential for social pack-hunting behaviour. The circumference of the distal humerus trochlea is found to be highly correlated with body mass, and appears to scale similarly throughout the order Carnivora. A general predictive model for carnivoran bodymass is presented (a=0.601; b= 2.552; r2=0.952, SEE=0.136, p<0001, n=92), which removes the need for the investigator to actively choose between the diverging estimates that different predictors and their equations often produce. At the elbow joint, manual manipulation and locomotion appear to be conflicting functions, thus suggesting mutually exclusive lifestyles involving either forelimb grappling or pursuit. At large body sizes, carnivorans are distributed over a strongly dichotomised pattern (grappling or locomotion), a pattern coinciding with the postulated threshold in predator-prey size ratio at 21.5-25 kg. This pattern is compared to that of two carnivoran faunas from the Tertiary. In the Oligocene (33.7-23.8 Myr BP), the overall pattern is remarkably similar to that observed for extant Carnivora. In the Miocene (23.8-11.2 Myr BP) carnivores show a similarly dichotomised pattern as the Oligocene and Recent, although the whole pattern is shifted towards larger body sizes. This difference is suggested to be a reflection of the extraordinary species richness of browsing ungulates in the early Miocene of North America. Such an increase in prey spectrum would create a unique situation, in which large carnivores need not commit to a cursorial habitus in order to fill their nutritional requirements. Finally, the elbow joints and craniodental morphology (14 measurements) of fossil canids were examined with the aim of assessing the potential for pack-hunting in fossil canids. It is clear that small and large members of the Recent Caninae share similar craniodental morphologies. However, this pattern is not present in Borophaginae and Hesperocyoninae. In the latter, large representatives are characterized by being short-faced, with reduced anterior premolars and enlarged posterior premolars, thus approaching a “pantherine-like” craniodental configuration. These traits are interpreted as an adaptation for killing prey with canine bites. It is similarly determined that, unlike recent Caninae, all analyzed species of borophagines and hesperocyonines have retained the ability to supinate their forearms. It is therefore likely that manual manipulation was part of their hunting behaviour, thus removing an essential part of the argument for social pack-hunting in these forms, as the benefits of such a strategy become less obvious.</p>

In this thesis, the shape of the distal humerus trochlea is analysed using landmark-based morphometrics and multivariate methods, with the aim of exploring locomotor evolution in carnivorans. Elbow joint morphology is used together with body size and craniodental morphology to characterize past and present carnivorans. Evolutionary implications are studied at the ordinal, familial, and species levels, testing specific hypotheses about scaling, morphological constraints, evolutionary trajectories, and potential for social pack-hunting behaviour. The circumference of the distal humerus trochlea is found to be highly correlated with body mass, and appears to scale similarly throughout the order Carnivora. A general predictive model for carnivoran bodymass is presented (a=0.601; b= 2.552; r2=0.952, SEE=0.136, p&lt;0001, n=92), which removes the need for the investigator to actively choose between the diverging estimates that different predictors and their equations often produce. At the elbow joint, manual manipulation and locomotion appear to be conflicting functions, thus suggesting mutually exclusive lifestyles involving either forelimb grappling or pursuit. At large body sizes, carnivorans are distributed over a strongly dichotomised pattern (grappling or locomotion), a pattern coinciding with the postulated threshold in predator-prey size ratio at 21.5-25 kg. This pattern is compared to that of two carnivoran faunas from the Tertiary. In the Oligocene (33.7-23.8 Myr BP), the overall pattern is remarkably similar to that observed for extant Carnivora. In the Miocene (23.8-11.2 Myr BP) carnivores show a similarly dichotomised pattern as the Oligocene and Recent, although the whole pattern is shifted towards larger body sizes. This difference is suggested to be a reflection of the extraordinary species richness of browsing ungulates in the early Miocene of North America. Such an increase in prey spectrum would create a unique situation, in which large carnivores need not commit to a cursorial habitus in order to fill their nutritional requirements. Finally, the elbow joints and craniodental morphology (14 measurements) of fossil canids were examined with the aim of assessing the potential for pack-hunting in fossil canids. It is clear that small and large members of the Recent Caninae share similar craniodental morphologies. However, this pattern is not present in Borophaginae and Hesperocyoninae. In the latter, large representatives are characterized by being short-faced, with reduced anterior premolars and enlarged posterior premolars, thus approaching a “pantherine-like” craniodental configuration. These traits are interpreted as an adaptation for killing prey with canine bites. It is similarly determined that, unlike recent Caninae, all analyzed species of borophagines and hesperocyonines have retained the ability to supinate their forearms. It is therefore likely that manual manipulation was part of their hunting behaviour, thus removing an essential part of the argument for social pack-hunting in these forms, as the benefits of such a strategy become less obvious.

Made available in DSpace on 2016-06-02T19:31:59Z (GMT). No. of bitstreams: 1 4017.pdf: 3689983 bytes, checksum: f15b289ba85e2141d06ae104015f2757 (MD5) Previous issue date: 2011-06-07 / The trophic ecology is one of the most important aspects to understand the role of a species in the community and in the ecosystem functioning. Studies regarding the feeding of fishes coupled to the ecomorphology of a species become important tools in understanding their ecological role and position in the environment. The present study aimed to analyze the types and amount of food consumed by eleven species of fishes collected in six streams of Alcântara, Maranhão state, and assess their possible interspecific interactions. The specimens were collected in the rainy season, in January, and in the dry season, in November 2008. The analysis of morphology of the fish species was performed by measuring 17 characteristics and calculating 16 ecomorphological attributes. Analysis of the contents of the digestive tract was performed quantitatively and qualitatively. In order to determine the feeding habits of each species the frequency of occurrence, volume and alimentary index of each food item consumed were calculated. The majority of individuals analyzed was collected in the streams Igarapé do Camarajó and Igarapé do Brito. The trophic structure of fish assemblages of these two streams was diversified in both, rainy and dry seasons. The habit of the benthivore species Micropoecilia cf. parae and Apistogramma cf. piauienses was corroborated by their morphology. In the rainy season, there was a higher niche overlap in the diet of insectivorous species in the stream Igarapé do Camarajó, but the morphology of these species showed distinct spatial occupation of the habitat, thus allowing their coexistence. In the dry season most species had food overlap due to the consumption of organic detritus in the Igarapé do Camarajó stream and due to the consumption of chironomid larvae in the Igarapé do Brito stream. Fishes of Camarajó and Brito streams were more likely to feeding specialization in the rainy season and increased diversification of the items consumed during the dry season, indicated, respectively, by larger and smaller niche breadth. The changes in the trophic structure, in the niche overlap and in the niche breadth of fish community in the six streams studied indicate that fluctuations on the hydrological cycle in these streams are an important factor in the throphic dynamics of these fish communities. / Um dos aspectos mais relevantes no entendimento do papel de uma espécie na comunidade à qual pertence e no funcionamento nos ecossistemas refere-se à sua ecologia trófica. Estudos sobre a alimentação de peixes atrelados à ecomorfologia das espécies são ferramentas importantes no entendimento do papel ecológico das espécies e de sua ocupação do meio. O presente estudo teve como objetivos estudar as características da alimentação e da ecomorfologia da ictiofauna amostrada em seis igarapés maranhenses e avaliar suas possíveis interações interespecíficas. Os exemplares analisados foram coletados na estação chuvosa, em janeiro, e na estação seca, em novembro, de 2008. Para análise da ecomorfologia destas espécies foram obtidas 17 medidas e com elas calculados 16 atributos ecomorfológicos. A análise do conteúdo do tubo digestório foi realizada quali e quantitativamente. Para a determinação do hábito alimentar de cada espécie foram calculados a frequência de ocorrência, o volume e o índice alimentar de cada item consumido. A maioria dos indivíduos analisados foi coletada nos igarapés do Camarajó e do Brito. A estrutura trófica da assembléia de peixes destes dois igarapés foi diversificada em ambas estações, chuvosa e seca. O hábito bentófago das espécies Micropoecilia cf. parae e Apistogramma cf. piauiensis foi corroborada por suas morfologias. Na estação chuvosa, observou-se maior sobreposição de nicho na dieta dos insetívoros no igarapé do Camarajó, porém, os atributos ecomofológicos destas espécies indicaram distinta ocupação de nicho espacial entre elas, permitindo, assim, a coexistência. Já na estação seca, no igarapé do Camarajó, a maioria das espécies teve sobreposição alimentar devido ao consumo de detritos orgânicos e no igarapé do Brito pelo consumo de quironomídeos. Os peixes dos igarapés do Camarajó e do Brito apresentaram maior tendência à especialização alimentar na estação chuvosa e maior diversificação dos itens consumidos na estação seca, ambas indicadas pela maior e menor amplitude de nicho, respectivamente. As mudanças na estrutura trófica, na sobreposição e no espectro alimentar da ictiofauna dos seis igarapés maranhenses estudados, indicam que as flutuações decorrentes do ciclo hidrológico constituem, nestes igarapés, um fator importante na dinâmica destas comunidades de peixes.