From video recordings to whisker stable isotopes: a critical evaluation of timescale in assessing individual foraging specialisation in Australian fur seals
- 641 Downloads
Estimating the degree of individual specialisation is likely to be sensitive to the methods used, as they record individuals’ resource use over different time-periods. We combined animal-borne video cameras, GPS/TDR loggers and stable isotope values of plasma, red cells and sub-sampled whiskers to investigate individual foraging specialisation in female Australian fur seals (Arctocephalus pusillus doriferus) over various timescales. Combining these methods enabled us to (1) provide quantitative information on individuals’ diet, allowing the identification of prey, (2) infer the temporal consistency of individual specialisation, and (3) assess how different methods and timescales affect our estimation of the degree of specialisation. Short-term inter-individual variation in diet was observed in the video data (mean pairwise overlap = 0.60), with the sampled population being composed of both generalist and specialist individuals (nested network). However, the brevity of the temporal window is likely to artificially increase the level of specialisation by not recording the entire diet of seals. Indeed, the correlation in isotopic values was tighter between the red cells and whiskers (mid- to long-term foraging ecology) than between plasma and red cells (short- to mid-term) (R 2 = 0.93–0.73 vs. 0.55–0.41). δ13C and δ15N values of whiskers confirmed the temporal consistency of individual specialisation. Variation in isotopic niche was consistent across seasons and years, indicating long-term habitat (WIC/TNW = 0.28) and dietary (WIC/TNW = 0.39) specialisation. The results also highlight time-averaging issues (under-estimation of the degree of specialisation) when calculating individual specialisation indices over long time-periods, so that no single timescale may provide a complete and accurate picture, emphasising the benefits of using complementary methods.
KeywordsArctocephalus pusillus Diet Nested network Time aggregating Vibrissae
The assistance of the many field workers involved in this study is gratefully acknowledged. The authors thank Bernard Cazelles for his precious contribution in the wavelet analysis, Gaël Guillou for running the isotopic analyses and Gaël Caro for his help in the analyses. The logistical support of Parks Victoria, in particular the Rangers from the Foster and Tidal River offices was crucial for the success of the study as was the skill and experience of the boat charter operator (Geoff Boyd). The research was financially supported by the Australian Research Council (DP110102065), Holsworth Wildlife Research Endowment and the Office of Naval Research (Marine Mammals and Biological Oceanography Program Award N00014-10-1-0385). All procedures were conducted under Deakin University Animal Ethics Committee Approval (A16/2008) and Department of Sustainability and Environment (Victoria) Wildlife Research Permits (10005362, 10005848) and all applicable institutional and/or national guidelines for the care and use of animals were followed.
Author contribution statements
LK and JPYA conceived the study design with meaningful input from YC. KA and GJM designed, developed and programmed for deployment the animal-borne video cameras and MAH and JS provided essential logistic support. JPYA and AJH collected the field data and samples. ND, DI and AB processed the video recordings and LK completed the laboratory work and performed the statistical analyses of the video and isotopic data. LK wrote the manuscript with significant editorial inputs from JPYA.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Franco-Trecu V, Aurioles-Gamboa D, Inchausti P (2013) Individual trophic specialisation and niche segregation explain the contrasting population trends of two sympatric otariids. Mar Biol 70:609–618Google Scholar
- Froese R, Pauly D (2014) FishBase, vol. 2014Google Scholar
- Furlani D, Gales R, Pemberton D (2007) Otoliths of common Australian temperate fish: a photographic guide. CSIRO, VictoriaGoogle Scholar
- Harris G, Griffiths F, Clementson L, Lyne V, Van der Doe H (1991) Seasonal and interannual variability in physical processes, nutrient cycling and the structure of the food chain in Tasmanian shelf waters. J Plankton Res 13:109–131Google Scholar
- Kleiber M (1961) The fire of life: an introduction to animal energetics. Wiley, New YorkGoogle Scholar
- Kuiter RH, Kuiter RH (1996) Guide to sea fishes of Australia. New Holland, SydneyGoogle Scholar
- Passlow V, O’Hara T, Daniell J, Beaman R (2004) Sediments and benthic biota of Bass Strait: an approach to benthic habitat mapping. Geoscience. Australia Record 23Google Scholar
- Ridgway K (2007) Long-term trend and decadal variability of the southward penetration of the East Australian current. Geophys Res Lett 34:L13613Google Scholar
- Svanbäck R, Bolnick DI (2005) Intraspecific competition affects the strength of individual specialization: an optimal diet theory method. Evol Ecol Res 7:993–1012Google Scholar