Isotopic niche of two coastal dolphins in a tropical marine area: specific and age class comparisons

Abstract

Niche differentiation is the process by which species evolve different forms of resource use, and is used to explain the co-occurrence in a variety of habitats. The Bayesian framework of isotopic niche through quantitative niche metrics was applied to estimate and compare the niche breadth of two sympatric coastal dolphins Pontoporia blainvillei and Sotalia guianensis in a tropical marine area. The standard ellipse areas (SEAs) based on species were quite similar, but the SEAs based on age class showed that the matures’ niche space is larger than the immatures’ for both dolphins. A probabilistic comparison of SEAs indicated that specific differences are negligible compared with age class differences. Trophic level measures (δ15N range) indicated that the dolphins are comparable as top predators, and that immature specimens have a lower range of trophic levels than mature ones. In terms of variability of food sources (δ13C range), S. guianensis showed a larger value than P. blainvillei and mature specimens had larger δ13C range than immatures for both species. In general, P. blainvillei and S. guianensis were similar in the niche metrics, with SEAs overlap of 52.1 and 39.7%. The immature specimens showed reduced isotopic niche overlap between species (<3%). In conclusion, Pontoporia blainvillei and S. guianensis specimens have similar isotopic niches, but pronounced differences between immature and mature specimens, both intraspecific and interspecific. Isotopic niche and quantitative metrics along with previous data on stomach contents provide a strong representation of species niche and their relationships.

Trophic dynamics in two South American estuaries encompassing industrial development and a biodiversity hotspot

“…The ratios δ 13 C and δ 15 N values among species groups observed here were similar to those in previous studies along the Brazilian coast, including for crustaceans (Bisi et al, 2012;Corbisier et al, 2006;Di Beneditto, et al, 2013), polychaetes, molluscs , cephalopods (Bisi et al,2012;Corbisier et al, 2006;Di Beneditto et al, 2012;Kehrig et al, 2013;, teleosts (S. rastrifer, P. brasileinsis and I. parvipinnis; Di Beneditto et al, 2012) and marine mammals (S. guianensis and P. blainvillei) (Baptista et al, 2016;Bisi et al, 2012;Di Beneditto & Monteiro, 2016;Kehrig et al, 2013). However, unlike some earlier studies in other Brazilian estuaries (e.g.…”

“…guianensis (Di Beneditto & Monteiro, 2016;Hardt et al, 2013;Lopes et al, 2012), sampling for teleosts was concentrated among their preferred prey of sciaenids, including rake stardrum,…”

“…Finer-scale assessment of ecological dependencies can be made by discussing speciesspecific values of δ 13 C and δ 15 N. Specifically, δ 13 C values are directly related to the spatialoccurrence patterns of each species (Cherel & Hobson, 2007;Di Beneditto & Monteiro, 2016).…”

“…More specifically, most delphinids have long life spans, feed at high trophic levels and are sensitive to environmental changes evoked through anthropogenic pressures (Moore, 2008;O'shea & Odell, 2008). Recognition of these traits means dolphins have long been used as ecological sentinels and for investigating contaminant transfer in many areas, including the south-western Atlantic Ocean (Bisi et al, 2012;Di Beneditto, Bittar, Camargo, Rezende, & Kehrig, 2012;Di Beneditto & Monteiro, 2016;Kehrig, Hauser-Davis, Seixas, Pinheiro, & Di Beneditto, 2016;Kehrig, Seixas, Malm, Di Beneditto, & Rezende, 2013). Exploring the trophic relationships of dolphins (or other marine mammals) via SI analyses is a coherent approach for elucidating broader potential threats to other species (Das et al, 2003;Smith et al, 1996).…”

“…Very few studies have assessed the trophic relationships of S. guianensis and P. blainvillei in southern Brazil, and these are restricted to the states of Rio de Janeiro (Bisi et al, 2013;Di Beneditto & Monteiro, 2016) and Santa Catarina (Hardt et al, 2013). Only one study has investigated δ 13 C and δ 15 N relationships in the CIELS, but this work focused on teleosts and…”