Individual trophic specialisation and niche segregation explain the contrasting population trends of two sympatric otariids

Franco‐Trecu, Valentina; Aurioles‐Gamboa, David; Inchausti, Pablo

doi:10.1007/s00227-013-2363-9

Cited by 60 publications

(54 citation statements)

References 65 publications

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“…However, the isotopic niche of South American fur seals from the Río de la Plata and the adjacent Atlantic coast progressively converged to that of the South American sea lion niche during the period 1991–2012 (Fig. ), although without actually overlapping it (Franco‐Trecu, Aurioles‐Gamboa & Inchausti ; this study). This progressive convergence of the isotopic niche was concurrent with the increasing trend of the South American fur seal population and the decreasing trend of the South American sea lion population in Uruguay (Franco‐Trecu ), as well as the reduction in the average size of striped weakfish (Villwock de Miranda & Haimovici ).…”

Section: Discussionmentioning

confidence: 50%

“…South American fur seals currently have a more pelagic diet than South American sea lions in the southwestern part of the South Atlantic (Franco‐Trecu, Aurioles‐Gamboa & Inchausti ; Saporiti et al . ), and stable isotope ratios of zooarchaeological bone material suggest that the same was also true during the second half of the Holocene (Saporiti et al .…”

Section: Introductionmentioning

confidence: 99%

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Isotopic niche partitioning between two apex predators over time

Drago

Cardona

Franco‐Trecu

et al. 2017

Journal of Animal Ecology

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Stable isotope analyses have become an important tool in reconstructing diets, analysing resource use patterns, elucidating trophic relations among predators and understanding the structure of food webs. Here, we use stable carbon and nitrogen isotope ratios in bone collagen to reconstruct and compare the isotopic niches of adult South American fur seals (Arctocephalus australis; n = 86) and sea lions (Otaria flavescens; n = 49) - two otariid species with marked morphological differences - in the Río de la Plata estuary (Argentina - Uruguay) and the adjacent Atlantic Ocean during the second half of the 20th century and the beginning of the 21st century. Samples from the middle Holocene (n = 7 fur seals and n = 5 sea lions) are also included in order to provide a reference point for characterizing resource partitioning before major anthropogenic modifications of the environment. We found that the South American fur seals and South American sea lions had distinct isotopic niches during the middle Holocene. Isotopic niche segregation was similar at the beginning of the second half of the 20th century, but has diminished over time. The progressive convergence of the isotopic niches of these two otariids during the second half of the 20th century and the beginning of the 21st century is most likely due to the increased reliance of South American fur seals on demersal prey. This recent dietary change in South American fur seals can be explained by at least two non-mutually exclusive mechanisms: (i) the decrease in the abundance of sympatric South American sea lions as a consequence of small colony size and high pup mortality resulting from commercial sealing; and (ii) the decrease in the average size of demersal fishes due to intense fishing of the larger class sizes, which may have increased their accessibility to those eared seals with a smaller mouth gape, that is, South American fur seals of both sexes and female South American sea lions.

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Section: Discussionmentioning

confidence: 50%

Section: Introductionmentioning

confidence: 99%

Isotopic niche partitioning between two apex predators over time

Drago

Cardona

Franco‐Trecu

et al. 2017

Journal of Animal Ecology

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“…), and South American fur seals ( Arctocephalus australis ) (Franco‐Trecu et al . ) that reported no differences in δ 13 C and δ 15 N values between the sexes. Our results show that subadult and adult males, however, had a larger isotopic niche width than females.…”

Section: Discussionmentioning

confidence: 89%

“…This is consistent with other isotope‐based studies of SASL in Uruguay (Franco‐Trecu et al . ), California sea lions ( Zalophus californianus ) in southern California (Orr et al . ), and South American fur seals ( Arctocephalus australis ) (Franco‐Trecu et al .…”

Section: Discussionmentioning

confidence: 99%

Spatial, temporal, age, and sex related variation in the diet of South American sea lions in southern Chile

Sepúlveda

Pavez

Santos‐Carvallo

et al. 2016

Marine Mammal Science

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We analyzed spatial, temporal, and age/sex variation in the diet of the South American sea lions (SASL, Otaria byronia) in southern Chile via δ13C and δ15N isotope analysis, with emphasis on exotic farmed and feral salmonids as a source of prey for this generalist predator. Isotope mixing models show that the primary prey consumed by SASL were demersal and benthopelagic fishes. Individuals sampled in summer and in the outer coast had higher δ15N values than those from winter or from the inner coast due to consumption of high trophic level demersal fish. We also found evidence of an ontogenetic shift in isotopic niche width as measured by δ13C and δ15N standard ellipse areas, with juveniles showing a restricted isotopic niche width (1.0‰2) in comparison to subadult (2.2‰2) and adult males (1.9‰2). The proportion of salmonids in the diet of the SASL was negligible and lower than reported in previous studies, which may be related to a recent drop in the production of salmon aquaculture in the region. Our study suggests that the SASL are able to adapt to shifts in spatiotemporal variations in the abundance of potential prey, including feral and farmed salmonids.

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“…Franco-Trecu, Aurioles-Gamboa, & Inchausti, 2014;Newsome et al, 2009); and (3) simultaneous sampling of different tissues (i.e. vibrissae, hair, otoliths, baleen, scutes), representing sequential archives over long periods of time (e.g.…”

Section: Introductionmentioning

confidence: 99%

An unbiased method to estimate individual specialisation from multi‐tissue isotopic data

Naya

Franco‐Trecu

2019

Freshwater Biology

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Individual specialisation could affect several ecological and evolutionary processes. Assessing isotopic data from different tissues of a single individual (multi‐tissue approach) represents a common method to estimate individual trophic specialisation (ITS). However, a neglected problem with this approach is that isotopic values of two tissues from a single individual are not statistically independent, and hence, an underestimation of the within‐individual component of variance should be theoretically expected. In this study, we evaluate this potential problem by comparing ITS estimations as currently calculated (uncorrected ITS) against ITS estimations based on a new method that considers the non‐independence problem (corrected ITS). We used unpublished δ15N and δ13C data for nine fish species, together with previously published δ15N and δ13C data for eight other vertebrate species, to estimate (and compare) components of variance and ITS values, using uncorrected and corrected isotopic data. In addition, for each species, we used a Monte Carlo resampling routine to test the null hypothesis that all individuals sample equally from the population diet distribution. We found that the use of uncorrected δ15N values provided an average ITS estimation which is, depending on the overlap among tissues turnover rates, 14%–35% (fish dataset) and 17%–40% (all species dataset) lower than estimations based on corrected values. Similarly, the use of uncorrected δ13C values provided an average ITS estimation which is 12%–29% (fish dataset) and 21%–45% (all species dataset) lower than corrected estimations. The implications of these results in an ecological context are of great significance. For instance, the fish dataset showed that while uncorrected estimations indicate that three (δ13C) or four (δ15N) species are trophic specialists at the individual level, a moderate correction in isotopic values indicate that none (δ13C) or only one (δ15N) species is a trophic specialist at that level. Noticeably, this last result is much more congruent with dietary data obtained from stomach content analysis. Given the several pros of the multi‐tissue approach, such as its reduced operative costs, we suggest not to abandon this method, but to cope with the non‐independence problem by using the correction proposed here or, at least, by selecting body tissues with a minimal overlap in their turnover rates.

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Individual trophic specialisation and niche segregation explain the contrasting population trends of two sympatric otariids

Cited by 60 publications

References 65 publications

Isotopic niche partitioning between two apex predators over time

Isotopic niche partitioning between two apex predators over time

Spatial, temporal, age, and sex related variation in the diet of South American sea lions in southern Chile

An unbiased method to estimate individual specialisation from multi‐tissue isotopic data

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