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Global climatic drivers of leaf size

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Science  01 Sep 2017:
Vol. 357, Issue 6354, pp. 917-921
DOI: 10.1126/science.aal4760

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  • RE: Global climatic drivers of leaf size
    • Timothy E. Moore, Graduate Student, University of Connecticut, Dept. of Ecology and Evolutionary Biology
    • Other Contributors:
      • James G. Mickley, Postdoctoral Research Associate, University of Connecticut, Dept. of Ecology and Evolutionary Biology
      • Cynthia S. Jones, Professor, University of Connecticut, Dept. of Ecology and Evolutionary Biology
      • Carl D. Schlichting, Professor, University of Connecticut, Dept. of Ecology and Evolutionary Biology

    The identification of the drivers of geographic variation in leaf shape has been a goal of ecology for centuries. In a significant step towards that goal, Wright et al. (1) use a large dataset of leaf size to investigate global patterns of leaf size variation in response to climate, and build energy balance models to predict the global upper limits of leaf size. They find that latitude and its associated climatic gradients capture considerable amounts of variation in leaf size (R-squared between 0.12 and 0.28). However, using the same modelling framework as Wright et al, we find that a model with family alone as a random effect captures nearly twice as much variation in Leaf Size (R-squared = 0.48), and has lower AIC, than any model that just includes individual climate variables as fixed effects. We find that a combination of site, species (both included in the Wright et al. models), and plant family captures substantially more of the variation in global leaf size than any of the climate variables they analyzed (with values of R-squared > 0.94). In fact, the ‘best’ models (based on AIC) include climate variables as fixed effects, and also site and taxonomic information as random effects (2). In this instance, non-climatic factors capture more of the variation in global leaf size. Global patterns of leaf size variation represent an amalgamation of disparate patterns among broadly and narrowly distributed plant families (2), some that range widely in leaf size and other...

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    Competing Interests: None declared.
  • RE: What Controls Maximum Leaf Size?
    • Adam J. Benfield, Graduate Student, Lehigh University; Dept. of Earth and Environmental Sciences
    • Other Contributors:
      • Dork Sahagian, Professor, Lehigh University; Dept. of Earth and Environmental Sciences
      • Stepehen C. Peters, Professor, Lehigh University; Dept. of Earth and Environmental Sciences

    In a remarkable paper relating biota to environment, Wright and colleagues (1) have produced a systematic, global analysis of variations in leaf size as a function of climatic drivers: growing season temperature, annual precipitation, annual moisture index, and annual daily irradiance. Their results are thought-provoking and lead us to suggest that there is an additional point of inquiry could further clarify the dependence of leaf size on local and regional environmental conditions. Here we suggest an aspect of climate that was not discussed by Wright et al.(1) and could potentially have stronger explanatory power for the determination of leaf size than shown in their figures 1B – 1E.
    Wright et al.’s energy balance model results (ref 1; Fig. 2) largely show a strong resemblance to global mean annual precipitation (MAP) distributions. However some notable areas of the world diverge from model results. Many tropical or sub-tropical areas experience large seasonal variations in precipitation amounts (2) due to monsoonal precipitation and the annual migration of the intertropical convergence zone (ITCZ). In those areas, many leaves begin their growth during the dry season (3), and are subject to drought stress during the early growing season. The Indian sub-continent, Southeast Asia, and sub-Saharan Africa all show far smaller leaf size than predicted on the basis of MAP alone.
    We suggest that in those areas, maximum leaf sizes could be limited by the length and...

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    Competing Interests: None declared.

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