Present address: Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University, Waurn Ponds Campus, Vic. 3217, Australia.
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Single-point isotope measurements in blood cells and plasma to estimate the time since diet switches
Article first published online: 18 FEB 2010
DOI: 10.1111/j.1365-2435.2010.01689.x
© 2010 The Authors. Journal compilation © 2010 British Ecological Society
Additional Information
How to Cite
Klaassen, M., Piersma, T., Korthals, H., Dekinga, A. and Dietz, M. W. (2010), Single-point isotope measurements in blood cells and plasma to estimate the time since diet switches. Functional Ecology, 24: 796–804. doi: 10.1111/j.1365-2435.2010.01689.x
Publication History
- Issue published online: 13 JUL 2010
- Article first published online: 18 FEB 2010
- Received 16 July 2009; accepted 12 January 2010 Handling Editor: Adam Kay
Keywords:
- isotopic clock;
- mathematical model;
- sensitivity analysis;
- stable carbon isotope;
- timing of events
Summary
1. Understanding ecological phenomena often requires an accurate assessment of the timing of events. To estimate the time since a diet shift in animals without knowledge on the isotope ratios of either the old or the new diet, isotope ratio measurements in two different tissues (e.g. blood plasma and blood cells) at a single point in time can be used. For this ‘isotopic-clock’ principle, we present here a mathematical model that yields an analytical and easily calculated outcome.
2. Compared with a previously published model, our model assumes the isotopic difference between the old and new diets to be constant if multiple measurements are taken on the same subject at different points in time. Furthermore, to estimate the time since diet switch, no knowledge of the isotopic signature of tissues under the old diet, but only under the new diet is required.
3. The two models are compared using three calibration data sets including a novel one based on a diet shift experiment in a shorebird (red knot Calidris canutus); sensitivity analyses were conducted. The two models behaved differently and each may prove rather unsatisfactory depending on the system under investigation. A single-tissue model, requiring knowledge of both the old and new diets, generally behaved quite reliably.
4. As blood (cells) and plasma are particularly useful tissues for isotopic-clock research, we trawled the literature on turnover rates in whole blood, cells and plasma. Unfortunately, turnover rate predictions using allometric relations are too unreliable to be used directly in isotopic-clock calculations.
5. We advocate that before applying the isotopic-clock methodology, the propagation of error in the ‘time-since-diet-shift’ estimation is carefully assessed for the system under scrutiny using a sensitivity analysis as proposed here.