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Advisor(s)
Abstract(s)
Compensatory growth (CG, accelerated growth that may occur when an
organism that has grown at a reduced rate as a result of suboptimal environmental
conditions is exposed to better conditions) is considered an adaptation to variable en vironments. Although documented thoroughly under captive conditions, CG has rarely
been studied in wild populations. In their first years of life, oceanic-stage loggerhead
sea turtles (Caretta caretta) have relatively little control over their geographic position
or movements and thus have an extremely stochastic lifestyle with great variation in
food availability and temperature. This environmental variation results in variable
growth rates. We evaluate somatic growth functions of oceanic-stage loggerheads from
the eastern Atlantic based on skeletochronology that allowed us to assign age and cohort
to each individual. We demonstrate CG in these turtles based on three different analytical
approaches: changes in coefficients of variation in size-at-age, generalized additive
model regression analyses of somatic growth, and linear regression of age-specific
growth rates. As a result of CG, variation in size-at-age in these juvenile loggerheads
is substantially reduced. Thus, size is a better predictor of age than expected based on
variation in growth rates. CG decreases with age, apparently as loggerheads gain greater
control over their movements. In addition, we have evaluated for the first time in wild
sea turtles the time-dependent nature of somatic growth by distinguishing among age,
year, and cohort effects using a mixed longitudinal sampling design with assigned-age
individuals. Age and year had significant effects on growth rates, but there was no
significant cohort effect. Our results address critical gaps in knowledge of the demog raphy of this endangered species.
Description
Keywords
Age–year–cohort effects Caretta caretta Compensatory growth Demography Marine turtle Skeletochronology Somatic growth Time-varying parameters . Faculdade de Ciências da Vida
Citation
Bjorndal, K. A., Bolten, A. B., Dellinger, T., Delgado, C., & Martins, H. R. (2003). Compensatory growth in oceanic loggerhead sea turtles: response to a stochastic environment. Ecology, 84(5), 1237-1249.
Publisher
Ecological Society of America