Foraging behaviour of mammals, namely the change in distribution and trophic levels from juvenile stage to adulthood, can be investigated by measuring δ 13 C and δ 15 N stable isotopes for layers deposited in a growing tooth. For the first time, we describe geographic differences in the ontogeny of foraging strategies and in the niche partitioning process according to sex and age of a highly sexually dimorphic species: the southern elephant seal Mirounga leonina. Canines from 8 males and 6 females were analysed for δ 13 C and δ 15 N stable isotope signatures. To assess intra-individual variability, instead of analysing collagen we analysed the bulk dentine within each of the 4 growth layers deposited annually. The δ 13 C signature revealed that, in individuals of 1 to 4 yr of age, teeth of both males and females exhibited large intra-individual variation in δ 13 C, suggesting that juveniles were foraging over a broad range of marine habitats encompassing both sub-Antarctic and Antarctic waters. Four out of the 6 teeth taken from females were collected on individuals younger than 4 yr, preventing investigation of longer-term changes. A δ 13 C pattern emerged for males older than 4 yr: individuals became resident to either a subAntarctic (-17 ‰) or an Antarctic (-20 ‰, both values reported as deviations from the Vienna PeeDee Belemnite standard) foraging habitat, with a decrease in intra-individual variability. Up to the age of 4 yr, juvenile males were at a slightly higher trophic level than juvenile females, but by the age of 4 yr, while their δ 13 C signature revealed that they were faithful to their foraging habitat, males exhibited a significant increase in their trophic levels, as shown by their δ Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 439: [295][296][297][298][299][300][301][302][303][304][305] 2011 techniques of stomach lavaging or faecal analysis may provide high-resolution species-specific data directly related to digestion transit rate, and over a relatively short period. Stable isotopes, while lacking in high-resolution species-specific data over a short timeframe, can reveal surprising ecological features of a species by summarizing trophic information over a broader time and space window as compared to traditional dietary studies. Stable isotopic carbon and nitrogen analysis is now increasingly used to investigate the feeding habits of major consumers (Newsome et al. 2007a, Newsome et al. 2010). The δ 15 N measurements serve as indicators of consumer trophic position, as consumer tissues are typically enriched in 15 N relative to their food (DeNiro & Epstein 1981, McCutchan et al. 2003, with an average increase of 3.3 ± 0.26 ‰ between trophic levels (McCutchan et al. 2003). In contrast, δ 13C values vary little between trophic levels but are often used to indi cate the geographic source of prey items due to well documented variation in δ 13C with different photo synthetic processes (Hobson 1999). In the marine environment, δ C...

Summary1. Stable isotopes are increasingly used in ecology to investigate ontogenetic shifts in foraging habitat (via d 2. In a Bayesian framework, we used a Cholesky decomposition for estimating a moderately-sized covariance matrix, thereby directly estimating correlations between parameters describing time-series of isotopic measurements. We offer guidelines on how to select the covariance structure. 3. The approach is illustrated with a hierarchical change-point (or broken stick) model applied to a data set collected on Southern Elephant Seals, Mirounga leonina. Ontogenetic shifts in foraging habitat, following a juvenile and variable stage, were detected and interpreted as fidelity to a foraging strategy; while ontogenetic shifts in trophic level were more likely the result of complete independence from maternal resources followed by a gradual increase in trophic level as seals aged. 4. Specifying both an appropriate covariance and mean structure enabled us to draw strong inferences on the ecology of an elusive marine predator, and has wide applicability for isotopic ecology provided repeated isotopic measurements are available.

Data concerning driftwood is of value to researchers in fields as diverse as oceanography, geomorphology, and human occupation. Yet studies on the subject in the Canadian Arctic have only recently been carried out, and the present study is the first in Nunavik (northeastern Canada). This paper documents the composition, characteristics, and origin of modern driftwood pieces on the beaches of the eastern coast of Hudson Bay. A total of 1057 samples from Ivujivik, Akulivik, Inukjuak, and Umiujaq were identified as belonging to four coniferous species (Picea sp., Larix sp., Abies sp. likely balsamea, and Thuja sp. likely occidentalis) and four deciduous species (Salix sp., Populus sp., Alnus sp., and Betula sp., likely papyrifera). Spruce largely predominate; white birch, white cedar, and fir are rare. The presence of the latter species proves that some of the wood originated from south-southeast of James Bay. Driftwood found in the southern area (Umiujaq) are more numerous, larger, and less degraded than driftwood in the north (Ivujivik). However, many large coniferous samples were found as far north as Akulivik, indicating that they likely traveled a great distance, unlike the smaller wood specimens (especially deciduous samples). All of the wood that we analyzed died relatively young, with an average age of 63 years for conifers and 23 years for deciduous. Measurements of ring widths and the cross-dating of samples with existing reference chronologies of living trees along Hudson Bay and James Bay revealed several possible correlations and origins for wood found in same areas.