Coupled dynamics of body mass and population growth in response to environmental change


Environmental change has altered the phenology, morphological traits and population dynamics of many species1,2. However, the links underlying these joint responses remain largely unknown owing to a paucity of long-term data and the lack of an appropriate analytical framework3. Here we investigate the link between phenotypic and demographic responses to environmental change using a new methodology and a long-term (1976–2008) data set from a hibernating mammal (the yellow-bellied marmot) inhabiting a dynamic subalpine habitat. We demonstrate how earlier emergence from hibernation and earlier weaning of young has led to a longer growing season and larger body masses before hibernation. The resulting shift in both the phenotype and the relationship between phenotype and fitness components led to a decline in adult mortality, which in turn triggered an abrupt increase in population size in recent years. Direct and trait-mediated effects of environmental change made comparable contributions to the observed marked increase in population growth. Our results help explain how a shift in phenology can cause simultaneous phenotypic and demographic changes, and highlight the need for a theory integrating ecological and evolutionary dynamics in stochastic environments4,5.

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Figure 1: Trends in the phenology, mean phenotypic trait and demography for females of the yellow-bellied marmot population.
Figure 2: The relationship between body mass and demographic and trait transition rates.
Figure 3: Trait-based analysis of the population dynamics.
Figure 4: Contributions of the changes in mean mass ( Z 1 to Z 2) and mass-survival relationship ( S 1 to S 2) to the increase in mean survival from <2000 to ≥2000.


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We thank the ‘marmoteers’ who participated in collecting the long-term data, Rocky Mountain Biological Laboratory for providing the field facilities, B. Barr and D. Inouye for providing additional information on climate and plant phenology, and L. M. Chevin, J. A. Hostetler, D. Inouye, N. J. Singh and I. M. Smallegange for comments. This work was funded by NERC, the Wellcome Trust, NSF, NIH and NIA.

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K.B.A. and D.T.B. led the long-term study; K.B.A., D.T.B., L.E.O. and A.O. collected data; A.O. and T.C. conceived the ideas for the paper and its structure; A.O., D.Z.C., T.C., M.K.O. and S.T. designed the analyses; A.O. and D.Z.C. conducted the analyses; A.O. wrote the manuscript; all authors discussed the results and commented on the manuscript.

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Correspondence to Arpat Ozgul.

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The authors declare no competing financial interests.

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Ozgul, A., Childs, D., Oli, M. et al. Coupled dynamics of body mass and population growth in response to environmental change. Nature 466, 482–485 (2010).

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