Abstract
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.
Highlights
Stable isotope analysis (SIA) has become the most common biochemical method used to study aquatic mammal trophic ecology (see[5])
In order to apply stable isotope analysis (SIA) to the study of the trophic and spatial ecology of marine predators, the patterns of baseline isotopic values along geographical gradients must be considered. These basal values are commonly used to generate maps of isotopic values which in turn provide a powerful approach to understanding the habitat use, foraging ecology and movements of p redators[20] as these baseline differences cascade up, with modifications associated with trophic transfer, to the top of the food webs
Excluding Sgui_AE from the analysis, a pattern of decreasing δ13C values was observed from inshore (i.e., S. bredanensis, T. truncatus) to offshore
Summary
Stable isotope analysis (SIA) has become the most common biochemical method used to study aquatic mammal trophic ecology (see[5]). The δ-space formed by the axis δ13C and δ15N, can be comparable to these scenopoetic and bionomic dimensions of the ecological niche, as isotopic values in a predator’s tissues represent both the prey it consumes (bionomic) and the habitat where it forages (scenopoetic)[13,14,16] This “isotopic niche” and its dimensions have been recently applied as an approach to study the trophic ecology and resource partitioning of several marine predators, such as baleen whales[17], toothed cetaceans[2,3,18], and sharks[19]. A better understanding of the trophic and spatial ecology of these aquatic mammals is needed to fill this knowledge gap
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