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Patterns of niche breadth and feeding overlap of the fish fauna in the seasonal Brazilian Pantanal, Cuiabá River basin

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Author(s): Carlos Eduardo Corrêa | Miriam Pilz Albrecht | Norma Segatti Hahn

Journal: Neotropical Ichthyology
ISSN 1679-6225

Volume: 9;
Issue: 3;
Start page: 637;
Date: 2011;
Original page

Keywords: Coexistence | Diet | Fishes | Floodplain | Pantanal

ABSTRACT
Spatial and temporal variations in patterns of niche breadth and feeding overlap were investigated for the fish fauna in the Pantanal region, aiming to determine the factors that account for species coexistence. Samples were conducted in the Cuiabá River and Chacororé pond, in the upper Pantanal region, Mato Grosso State, Brazil, during one hydrological cycle (March 2000 to February 2001), (designed spatial-seasonal units). Mean niche breadth values were overall low for the fish assemblage (0.2-0.3). Differences between periods were not statistically significant. Feeding overlap values ranged between 0 and 0.4, whereas the mean was always inferior to 0.05 in all spatial-temporal units, and differences between periods were not statistically significant. The highest and lowest mean values were both observed in the pond; the former during the drought period and the latter during the flood period. All feeding overlap mean values were significantly higher than the values expected at random in the null model, using both "scrambled-zeros" (RA3) and "conserved-zeros" (RA4) algorithms. Thus, the foraging patterns show evidences of food sharing. The variance generated in the null model had a pattern similar to the niche overlap pattern: observed variance was higher than expected by chance in all spatial-temporal units, suggesting that the fish fauna is structured in trophic guilds. The patterns of food resource use and the different trophic guilds identified, suggest that species probably have different roles in this ecosystem. Our results suggest that food sharing allows coexistence of different fish species.Foram investigadas variações espaço-temporais nos padrões de amplitude de nicho e sobreposição alimentar da ictiofauna de uma região do Pantanal, com o objetivo de determinar os fatores responsáveis pela coexistência das espécies. Os peixes foram coletados no rio Cuiabá e na lagoa Chacororé, na região superior do Pantanal de Mato Grosso, Brasil, durante um ciclo hidrológico (março de 2000 a fevereiro de 2001) (designada unidade espaço-temporal). De modo geral, a ictiofauna apresentou baixos valores de amplitude de nicho trófico, sendo que as médias variaram entre 0,2 e 0,3 e não apresentaram diferenças significativas. Os valores de sobreposição alimentar foram igualmente baixos, entre 0 e 0,4 e as medianas em cada unidade espaço-temporal foram inferiores a 0,05, sendo que as diferenças não foram significativas. Os maiores e menores valores médios foram observados na lagoa, durante a seca e cheia, respectivamente, sendo essas diferenças significativas. Os valores médios de sobreposição alimentar foram significativamente maiores do que os esperados ao acaso no modelo nulo, usando tanto a opção de zeros embaralhados (RA3) quanto a de zeros retidos (RA4). Assim, os padrões de forrageamento das espécies mostraram evidência de compartilhamento de recursos alimentares. A variância acompanhou o mesmo padrão da sobreposição de nicho, sendo aquela observada sempre maior que a esperada ao acaso, indicando que a ictiofauna, de modo geral, é estruturada em guildas. Assim, os resultados desse estudo sugerem que o compartilhamento de recursos alimentares permite a coexistência das diferentes espécies.
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