Intraskeletal variability in stable isotope ratios of C and N among pinnipeds and cetaceans

Establishing patterns of movement of wild animals is crucial for our understanding of their ecology, life history and behavior, and is a prerequisite for their effective conservation. Advances in the use of stable isotope markers make it possible to track a diversity of animal species in a variety of habitats. This approach is revolutionizing the way in which we make connections between phases of the annual cycle of migratory animals. However, researchers must exercise care in their application of isotopic methods. Here, we review stable isotope patterns in nature and discuss recent tracking applications in a range of taxa. To aid in the interpretation and design of effective and insightful isotope movement studies, we discuss a series of key issues and assumptions. This exciting field will advance rapidly if researchers consider these aspects of study design and interpretation carefully.

We have measured the (14)C content of human femoral mid-shaft collagen to determine the dynamics of adult collagen turnover, using the sudden doubling and subsequent slow relaxation of global atmospheric (14)C content due to nuclear bomb testing in the 1960s and 1970s as a tracer. (14)C measurements were made on bone collagen from 67 individuals of both sexes who died in Australia in 1990-1993, spanning a range of ages at death from 40 to 97, and these measurements were compared with values predicted by an age-dependent turnover model. We found that the dataset could constrain models of collagen turnover, with the following outcomes: 1) Collagen turnover rate of females decreases, on average, from 4%/yr to 3%/yr from 20 to 80 years. Male collagen turnover rates average 1.5-3%/yr over the same period. 2) For both sexes the collagen turnover rate during adolescent growth is much higher (5-15%/yr at age 10-15 years), with males having a significantly higher turnover rate than have females, by up to a factor of 2. 3) Much of the variation in residual bomb (14)C in a person's bone can be attributed to individual variation in turnover rate, but of no more than about 30% of the average values for adults. 4) Human femoral bone collagen isotopically reflects an individual's diet over a much longer period of time than 10 years, including a substantial portion of collagen synthesised during adolescence.