Intrinsic and extrinsic forcing in life histories: patterns of growth and stable isotopes in male Antarctic fur seal teeth

Hanson, N.N., Wurster, C.M., Bird, M.I., and Boyd, I.L. (2009) Intrinsic and extrinsic forcing in life histories: patterns of growth and stable isotopes in male Antarctic fur seal teeth. Marine Ecology Progress Series, 388. pp. 263-272.

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Life-time records of the trophic sources of carbon, nitrogen and of growth rate can be generated from biogenic structures that show accretionary growth, including fish scales, whale baleen and the teeth of some animals. Records generated from individual teeth can also be combined to provide longer time series elucidating changes in environmental conditions encountered by a population. Both intrinsic (i.e. ontogenetic) and extrinsic (i.e. environmental) factors are important in modulating variation in growth and the apparent dietary sources of C and N. We used the canine teeth of a large marine predator, the male Antarctic fur seal Arctocephalus gazella from South Georgia, to investigate both intrinsic and extrinsic sources of variation. Substantial ontogenetic shifts occurred in both δ13C and δ15N values in individual teeth, indicating a change in the trophic sources of C and N as individual animals age. Over the 40 yr period from 1964 to 2005, and after statistical reduction of ontogenetic variation, we also detected long-term declines in δ13C and δ15N values, indicating that the population has become more dependent on energy from a lower trophic level. A concurrent decline in annular tooth growth may be a consequence of rapid population growth during this period. The time series of δ13C values was also inversely correlated with sea surface temperatures in the region, although isolating a causal relationship remains elusive. Our analyses suggest that both intrinsic and extrinsic sources of variation, and their interaction, must be considered from such time series data; failure to do so could result in a biased interpretation.

Item ID: 10867
Item Type: Article (Research - C1)
ISSN: 1616-1599
Keywords: annulus; dietary reconstruction; stable isotope; time series analysis; Southern Ocean
Date Deposited: 25 May 2010 23:43
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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