Fossil leaf economics quantified

Calibration, Eocene case study, and implications

Dana L. Royer*, Lawren Sack, Peter Wilf, Christopher H. Lusk, Gregory J. Jordan, Ülo Niinemets, Ian J. Wright, Mark Westoby, Bárbara Cariglino, Phyllis D. Coley, Asher D. Cutter, Kirk R. Johnson, Conrad C. Labandeira, Angela T. Moles, Matthew B. Palmer, Fernando Valladares

*Corresponding author for this work

Research output: Contribution to journalArticle

80 Citations (Scopus)

Abstract

Leaf mass per area (MA) is a central ecological trait that is intercorrelated with leaf life span, photosynthetic rate, nutrient concentration, and palatability to herbivores. These coordinated variables form a globally convergent leaf economics spectrum, which represents a general continuum running from rapid resource acquisition to maximized resource retention. Leaf economics are little studied in ancient ecosystems because they cannot be directly measured from leaf fossils. Here we use a large extant data set (65 sites; 667 species-site pairs) to develop a new, easily measured scaling relationship between petiole width and leaf mass, normalized for leaf area; this enables MA estimation for fossil leaves from petiole width and leaf area, two variables that are commonly measurable in leaf compression floras. The calibration data are restricted to woody angiosperms exclusive of monocots, but a preliminary data set (25 species) suggests that broad-leaved gymnosperms exhibit a similar scaling. Application to two well-studied, classic Eocene floras demonstrates that MA can be quantified in fossil assemblages. First, our results are consistent with predictions from paleobotanical and paleoclimatic studies of these floras. We found exclusively low-MA species from Republic (Washington, U.S.A., 49 Ma), a humid, warm-temperate flora with a strong deciduous component among the angiosperms, and a wide MA range in a seasonally dry, warm-temperate flora from the Green River Formation at Bonanza (Utah, U.S.A, 47 Ma), presumed to comprise a mix of short and long leaf life spans. Second, reconstructed MA, in the fossil species is negatively correlated with levels of insect herbivory, whether measured as the proportion of leaves with insect damage, the proportion of leaf area removed by herbivores, or the diversity of insect-damage morphotypes. These correlations are consistent with herbivory observations in extant floras and they reflect fundamental trade-offs in plant-herbivore associations. Our results indicate that several key aspects of plant and plant-animal ecology can now be quantified in the fossil record and demonstrate that herbivory has helped shape the evolution of leaf structure for millions of years.

Original languageEnglish
Pages (from-to)574-589
Number of pages16
JournalPaleobiology
Volume33
Issue number4
DOIs
Publication statusPublished - Sep 2007

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    Royer, D. L., Sack, L., Wilf, P., Lusk, C. H., Jordan, G. J., Niinemets, Ü., ... Valladares, F. (2007). Fossil leaf economics quantified: Calibration, Eocene case study, and implications. Paleobiology, 33(4), 574-589. https://doi.org/10.1666/07001.1