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

Carlos Eduardo Corrêa,Miriam Pilz Albrecht,Norma Segatti Hahn

doi:10.1590/s1679-62252011000300017

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.

Highlights

Patterns of resource utilization are a fundamental property of ecological systems (Winemiller & Pianka, 1990), aiming to assess the role of interspecific competition on the coexistence of a great number of species (Schoener, 1974)
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
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

Summary

Introduction

Patterns of resource utilization are a fundamental property of ecological systems (Winemiller & Pianka, 1990), aiming to assess the role of interspecific competition on the coexistence of a great number of species (Schoener, 1974). Coexisting species may reflect niche partitioning at variable spatial and temporal scales. Niche overlap measures determine the degree of resource segregation among species, but might provide a descriptive measure of assemblage organization. Low values of niche overlap indicate that species are more segregated in the environment. Food and space are recognized as the major resource axes for niche partitioning in vertebrates (Schoener, 1974), and in aquatic systems food is recognized as the main axis (Ross, 1986). Several studies carried out in aquatic systems (e.g., Prejs & Prejs, 1987; Hahn et al, 2004; Mérona & Rankin-deMérona, 2004; Pouilly et al, 2003, 2004, 2006; Novakowski et al, 2008) have demonstrated that the same food resource can be shared by several species, and that each species might explore many different resources

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