TY - JOUR
T1 - Individual trophic specialisation and niche segregation explain the contrasting population trends of two sympatric otariids
AU - Franco-Trecu, Valentina
AU - Aurioles-Gamboa, David
AU - Inchausti, Pablo
N1 - Funding Information:
Acknowledgments We are very grateful with L. Olivera, N. Veiga, M. Casella, R. Frau, H. Katz, M. García and F. Riet for their assistance and logistical support during fieldwork. We also thank Lab. de Ecología de Pinnípedos B.J. Le Boeuf Staff (CICIMAR), especially to Ligia Rivera, for their help with laboratory work. We thank CSIC (Council for Scientific Research) of the Universidad de la República, Rufford Maurice Lain Foundation, ONG Yaqu-pacha and Heidelberg Zoo for funding this research. VFT was funded by a PhD scholarship by the ANII (National Agency for Research and Innovation, Uruguay) and received a travel award from PEDECIBA (Programme for the Development of Basic Sciences, Uruguay). We acknowledge DINARA (National Council for Aquatic Resources, Ministry of Livestock, Agriculture and Fishing, Uruguay) for allowing access to the field sites and facilities during 2009 and 2010 (permits 572/2008 and 1022/2010). The authors declare that they have no conflict of interest.
PY - 2014/3
Y1 - 2014/3
N2 - Individual specialisation is increasingly recognised to be an ecological and evolutionary process having important consequences for population dynamics of vertebrates. The South American fur seal (SAFS) and the South American sea lion (SASL) are two otariid species with similar ecology that coexist in sympatry in the Uruguayan coast. These two species have contrasting trends and widely different population sizes. The underlying reasons for these population trends, unique in their geographical ranges, remain unknown. We studied the foraging ecology of these otariid species over 2 years at the individual- and population levels using the isotopic ratios (δ13C-δ15N) in whiskers of both sexes. We compared the isotope ratios between species and sexes and used several metrics to characterise the degree of overlap and distinctiveness in the use of isotopic niche space at the individual- and population levels. Interspecific trophic niche overlap was minimal, thus ruling out interspecific competition as the cause for the contrasting population trends of both species. At the intraspecific level, both species had sexual segregation in their foraging areas, but each species had a large overlap in the isotopic niches between sexes. While SAFS had a wider niche and generalist individuals, SASL had the narrower niche with a higher degree of individual specialisation. Behavioural constraints during the breeding season, intraspecific competition and a major dependence on resources of the Uruguayan coastal shelf may explain why SASL had a higher trophic individual specialisation and a larger vulnerability in a heavily exploited habitat by fisheries and, by consequence, a locally declining population trend.
AB - Individual specialisation is increasingly recognised to be an ecological and evolutionary process having important consequences for population dynamics of vertebrates. The South American fur seal (SAFS) and the South American sea lion (SASL) are two otariid species with similar ecology that coexist in sympatry in the Uruguayan coast. These two species have contrasting trends and widely different population sizes. The underlying reasons for these population trends, unique in their geographical ranges, remain unknown. We studied the foraging ecology of these otariid species over 2 years at the individual- and population levels using the isotopic ratios (δ13C-δ15N) in whiskers of both sexes. We compared the isotope ratios between species and sexes and used several metrics to characterise the degree of overlap and distinctiveness in the use of isotopic niche space at the individual- and population levels. Interspecific trophic niche overlap was minimal, thus ruling out interspecific competition as the cause for the contrasting population trends of both species. At the intraspecific level, both species had sexual segregation in their foraging areas, but each species had a large overlap in the isotopic niches between sexes. While SAFS had a wider niche and generalist individuals, SASL had the narrower niche with a higher degree of individual specialisation. Behavioural constraints during the breeding season, intraspecific competition and a major dependence on resources of the Uruguayan coastal shelf may explain why SASL had a higher trophic individual specialisation and a larger vulnerability in a heavily exploited habitat by fisheries and, by consequence, a locally declining population trend.
UR - http://www.scopus.com/inward/record.url?scp=84897575059&partnerID=8YFLogxK
U2 - 10.1007/s00227-013-2363-9
DO - 10.1007/s00227-013-2363-9
M3 - Artículo
SN - 0025-3162
VL - 161
SP - 609
EP - 618
JO - Marine Biology
JF - Marine Biology
IS - 3
ER -