Abstract
We investigated the niche breadth and overlap of the fish species occurring in four environments affected by the Coaracy Nunes reservoir, in the Amapá Brazilian State. Seasonal samples of fishes were taken using a standard configuration of gillnets, as well as dragnets, lines, and cast-nets. Five hundred and forty stomach contents, representing 47 fish species were analyzed and quantified. Niche breadth and overlap were estimated using indexes of Levins and Pianka, respectively, while interspecific competition was evaluated using a null model (RA3). ANOVA and the Kruskal-Wallis test were used, respectively, to evaluate differences in niche breadth and overlap between areas. The data indicate that the majority of the fish species belong to the piscivore, omnivore, and detritivore guilds. These species have likely colonized the environments due to the availability of suitable feeding resources, and the favorable physical conditions created by the river damming. Overall, few species have ample niches, but most of them are highly specialized. Resources seasonal variation had little effect on the feeding behavior of most species in the study areas. The null models indicated that competition was not a factor determining on community structure.
Highlights
Understanding the ecological mechanisms that support the coexistence of species in a given community and their partitioning of resources is one of the fundamental objectives of the ecological investigation of Neotropical fish assemblages (Cassemiro et al 2008)
Niche breadth is an important parameter for the evaluation of the level of dietary specialization
Four areas influenced by the Coaracy Nunes reservoir (Fig. 1) were discriminated: 1 - Downriver Area (DWN): located downstream from the dam, this area presents lotic characteristics with the flow of water being influenced by the control of the dam’s flood gates and the discharge of the turbines in the hydro-electric power station, which it could create areas with reduced flow; 2 - Reservoir (RES): main body of the reservoir, with semi-lotic characteristics intermediate between those of a river and a lake; 3 - Lacustrine (LAK): an area adjacent to the reservoir, with extremely lentic characteristics; 4 - Upriver Area (UPR): area upstream from the reservoir with lotic conditions
Summary
Understanding the ecological mechanisms that support the coexistence of species in a given community and their partitioning of resources is one of the fundamental objectives of the ecological investigation of Neotropical fish assemblages (Cassemiro et al 2008). Niche breadth is an important parameter for the evaluation of the level of dietary specialization. The analysis of niche overlap provides an important approach for the evaluation of the structuring of communities in terms of the feeding niches of the different species that compose them (Corrêa et al 2011). The degree of specialization for the exploitation of specific types of resources could be used to classify groups of species in feeding guilds (Winemiller and Pianka 1990)
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