Dear MARMAM colleagues,
We are pleased to share our new article published in /Ecology and
Evolution/:
Planque Y, Spitz J, Authier M, Guillou G, Vincent C, Caurant F. Trophic
niche overlap between sympatric harbour seals (/Phoca vitulina/) and
grey seals (/Halichoerus grypus/) at the southern limit of their
European range (Eastern English Channel). Ecol Evol. 2021;00:1– 22.
(/Abstract below/)
The article is freely available online from
https://doi.org/10.1002/ece3.7739 <https://doi.org/10.1002/ece3.7739>
(Open Access).
For people interested by the analyses used in this study, all materials
(data and R scripts) are publicly accessible from these links:
*→*scat contents data (https://doi.org/10.17882/76780
<https://doi.org/10.17882/76780>) used for diet analysis (diet clusters
and overlap) (https://github.com/YannPlanque/Diet_Cluster_and_Overlap
<https://github.com/YannPlanque/Diet_Cluster_and_Overlap>)
*→*stable isotopes data (https://doi.org/10.17882/76528
<https://doi.org/10.17882/76528>) used to identify isotopic niches witha
novel hierarchical Bayesian model considering both intra- and
interindividual variability
(https://github.com/YannPlanque/Isotopic_Niche_Overlap
<https://github.com/YannPlanque/Isotopic_Niche_Overlap>)
*→*dive data from telemetry tracking (https://doi.org/10.17882/80016
<https://doi.org/10.17882/80016>) used to identify foraging areas
(https://github.com/YannPlanque/Foraging_Areas_with_Dive_Data
<https://github.com/YannPlanque/Foraging_Areas_with_Dive_Data>)
All the best,
Yann Planque and co-authors
*_Abstract_*: Sympatric harbour (/Phoca vitulina/) and grey seals
(/Halichoerus grypus/) are increasingly considered potential
competitors, especially since recent local declines in harbour seal
numbers while grey seal numbers remained stable or increased at their
European core distributions. A better understanding of the interactions
between these species is critical for conservation efforts. This study
aimed to identify the trophic niche overlap between harbour and grey
seals at the southern limit of their European range, in the Baie de
Somme (BDS, Eastern English Channel, France), where numbers of resident
harbour seals and visiting grey seals are increasing exponentially.
Dietary overlap was identified from scat contents using hierarchical
clustering. Isotopic niche overlap was quantified using δ^13 C and δ^15
N isotopic values from whiskers of 18 individuals, by estimating
isotopic standard ellipses with a novel hierarchical model developed in
a Bayesian framework to consider both intraindividual variability and
interindividual variability. Foraging areas of these individuals were
identified from telemetry data. The three independent approaches
provided converging results, revealing a high trophic niche overlap due
to consumption of benthic flatfish. Two diet clusters were dominated by
either small or large benthic flatfish; these comprised 85.5% [CI95%:
80.3%–90.2%] of harbour seal scats and 46.8% [35.1%–58.4%] of grey seal
scats. The narrower isotopic niche of harbour seals was nested within
that of grey seals (58.2% [22.7%–100%] overlap). Grey seals with
isotopic values similar to harbour seals foraged in coastal waters close
to the BDS alike harbour seals did, suggesting the niche overlap may be
due to individual grey seal strategies. Our findings therefore provide
the basis for potential competition between both species (foraging on
benthic flatfish close to the BDS). We suggest that a continued increase
in seal numbers and/or a decrease in flatfish supply in this area could
cause/amplify competitive interactions and have deleterious effects on
harbour seal colonies.
--
Yann Planque
Doctorant / PhD student
*La Rochelle Université*
Centre d'Etudes Biologiques de Chizé (CEBC, UMR 7372 CNRS/ULR)
Centre Commun d'Analyses
5 allée de l'Océan, 17 000 La Rochelle, France
Tel: +33 (0)5 46 50 76 42
www.cebc.cnrs.fr <http://www.cebc.cnrs.fr>
www.univ-larochelle.fr <http://www.univ-larochelle.fr>
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