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

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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.

At a glance


  1. Trends in the phenology, mean phenotypic trait and demography for females of the yellow-bellied marmot population.
    Figure 1: Trends in the phenology, mean phenotypic trait and demography for females of the yellow-bellied marmot population.

    ac, Time of weaning (−0.17 days per year, P<0.01) (a), mean 1 August mass ( ) (b), and abundance in each age class (c). The four age classes are juvenile (<1 yr), yearling (1 yr-old), subadult (2 yrs-old) and adult (≥3 yrs-old). Subadult and adult masses are combined (older) in b. Vertical dotted lines delineate different phases of population dynamics.

  2. The relationship between body mass and demographic and trait transition rates.
    Figure 2: The relationship between body mass and demographic and trait transition rates.

    ac, Effect of body mass on survival (a), juvenile growth (b) and adult reproduction (c) for pre-2000 (<2000) and post-2000(≥2000) years. Shaded areas indicate the 95% confidence intervals, and rugs below and above the graph represent the distribution of the body mass data for <2000 and≥2000, respectively.

  3. Trait-based analysis of the population dynamics.
    Figure 3: Trait-based analysis of the population dynamics.

    a, Stable August log-body-mass distributions (lines) for juveniles and older individuals for <2000 and≥2000. Vertical lines show the mean body masses. Bars indicate the actual observed distribution over the entire study period. b, c, Retrospective perturbation analysis of the integral projection model gives the relative contribution of each function to population growth (b) and to change in mean adult body mass (c) from the <2000 to the≥2000 period (G, growth; L, litter size; Q, offspring mass; R, reproduction probability; S, survival; numbers indicate the age classes).

  4. Contributions of the changes in mean mass (Z1 to Z2) and mass-survival relationship (S1 to S2) to the increase in mean survival from <2000 to[thinsp][ge]2000.
    Figure 4: Contributions of the changes in mean mass (Z1 to Z2) and mass-survival relationship (S1 to S2) to the increase in mean survival from <2000 to≥2000.

    The proximity of the triangle (S1(Z2)) to the circle (S1(Z1)) versus to the diamond (S2(Z2))] indicates the contributions of the change in mean mass versus the change in survival curve for each age class. Confidence intervals indicate the process variation estimated using the particular mass distribution and survival function.


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Author information


  1. Department of Life Sciences, Imperial College London, Ascot, Berkshire SL5 7PY, UK

    • Arpat Ozgul &
    • Tim Coulson
  2. Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK

    • Dylan Z. Childs
  3. Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, Florida 32611, USA

    • Madan K. Oli
  4. Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas 66045, USA

    • Kenneth B. Armitage
  5. Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095, USA

    • Daniel T. Blumstein &
    • Lucretia E. Olson
  6. Department of Biology, Stanford University, Stanford, California 94305, USA

    • Shripad Tuljapurkar


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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