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Linking functional traits to ecological processes

Biodiversity and ecosystem function

Understanding the relationships between biodiversity and ecosystem functioning remains an important issue in ecology, even after 20 years of intensive research. Recently, Maestre et al.(2012) provided the first global study of the relationship between plant species richness and a variety of ecosystem processes linked to nutrient cycling in the world's major dryland ecosystems. A positive relationship was found between biodiversity and ecosystem multifunctionality (B-EMf), but it was statistically weak (R2 = 0.03) and that made us curious. Tommaso Jucker from our group re-analysed the dryland dataset having first classified sites into low, medium and high "stress" categories. He found that the strength of the B-EMf relationship changed consistently along the "stress" gradients, becoming strongly positive in the most "stressed" habitats (R2 = 0.22). Science published our findings as a Technical Comment1, but our approach was criticised by Maestre et al. in a response article. These criticisms arose because Maestre et al. misunderstood the way we had transformed data prior to analysis, and didn't seek clarification from us before publication. For further details read here and see our online comment on the Science website.

  1. Jucker, T., & Coomes, D.A. (2012) Comment on "Plant species richness and ecosystem multifunctionality in global drylands". Science, 337(6091), 155. link

Trait hierarchies not phylogenetic similarity as determinants of competition

As molecular phylogenies become relatively straightforward constructs, a number of recent papers have attempted to use phylogenetic information to make inferences about the processes structuring plant communities. Using the vast French Forest Inventory, we determined 275 interaction coefficients among tree species in the alps. We showed that competitive interaction strengths between pairs of tree species are closely related to their positions in species' trait hierarchy and not to their phylogenetic similarity . It seems to be generating some interesting debate! See the original article here: DOI link

  1. Kunstler, G., Lavergne, S., Courbaud, B., Thuiller, W., Vieilledent, G., Zimmermann, N. E., Coomes, D.A. (2012) Competitive interactions between forest trees are driven by species' trait hierarchy, not phylogenetic or functional similarity: Implications for forest community assembly. Ecology Letters, 15(8), 831-840.

Functional significance of seeds size variation

When David Coomes showed Professor Grubb (at that time his PhD supervisor) around his field site in the Venezuelan rain forests, he pointed out that species growing on white-sand soils appeared to have smaller seeds than congeners on better soils nearby. Frenzied data collection during the brief visit confirmed these observations1. The smaller seed sizes were interpreted in terms of a major advantage of keeping up seed number outweighing the marginal advantages of larger seed size1. Another seed-size study involved providing wild British rodents with seeds of 12 species in a "cafeteria trial"; we found that seed predation was not controlled by seed size, as we had hypothesised, because the effects of toxicity and woodiness of the seed coat outweighed any selection there may have been for larger seeds3. A third piece of work on seed size variation arose from a Science paper by Moles et al. showing that the greatest divergences in seed size among the flowering plants have been associated overwhelmingly with the differentiation between (i) shorter and taller plants and (ii) temperate and tropical plants. We supported the general thrust of this paper, but disagreed with their interpretation that the association of greater seed size with greater plant height could be understood in terms of Charnov's life-history theory for mammals, according to which “offspring size is coordinated with size at adulthood, because larger offspring offset the low survivorship to adulthood that would otherwise be a consequence of longer juvenile periods”. If Charnov's idea were to be applicable to plants, we would expect to see a simple correlation between seed size and adult plant height (as is found for offspring size in mammals) rather than the “wedge-shaped relationship” commonly observed. To give just one example, the enormous strangling figs of tropical rainforests have tiny seeds. This worked linked closely with David Coomes' interest at the time in the competition-colonisation trade-off as a mechanism of coexistence. We also showed how seed size was constrained biomechanically, leading to close correlations among inflorescence size, twig diameter, and leaf area (i.e. “Corner's Rules”)3.

  1. Grubb, P.J. & Coomes, D.A. (1997) Seed mass and nutrient content in nutrient-starved tropical rainforest in Venezuela. Seed Science Research, 7, 269-280. click
  2. Kollmann, J., Coomes, D.A., & White, S.M. (1998) Consistencies in post-dispersal seed predation of temperate fleshy-fruited species among seasons, years and sites. Functional Ecology, 12, 683-690. click
  3. Grubb, P.J., Coomes, D.A. & Metcalfe, D.J.(2005) Comment on "A brief history of seed size". Science, 310, 783A-783A. click  

Leaves and leaf litter

  1. Wright, D.M., Jordan, G.J., Lee, W.G., Duncan, R.P., Forsyth, D.M., & Coomes, D.A. (2010) Do leaves of plants on phosphorus-impoverished soils contain high concentrations of phenolic defence compounds? Functional Ecology 24, 52-61. DOI link
  2. Hoorens, B, Coomes, D.A., Aerts, R. (2010) Neighbour identity hardly affects litter mixture effects on decomposition rates of New Zealand forest species. Oecologia 162, 479-89. DOI link
  3. Grubb,P.J., Jackson, R.V., Barberis, I.M., Bee, J.N., Coomes, D.A., Dominy, N.J., De La Fuente, M.A.S. Lucas, P.W., Metcalfe, D.J., Svenning, J.C., Turner, I.M. & Vargas O. (2008) Monocot leaves are eaten less than dicot leaves in tropical lowland rain forests: correlations with toughness and leaf presentation. Annals of Botany 101, 1379-1389 DOI link pdf (password needed)

Stems and deadwood

  1. Chave, J., Coomes,D.A, Jansen, S., Lewis, S., Swenson, N., Zanne, A. (2009) Towards a worldwide wood economics spectrum. Ecology Letters, 12, 351-366 DOI link pdf
  2. Russo S.E., Jenkins K.L., Wiser S.K., Uriarte M., Duncan R.P., Coomes D.A. (2010) Interspecific relationships among growth, mortality and xylem traits of woody species from New Zealand. Functional Ecology 24: 253-262.
  3. Weedon, J., Cornwell, W., Cornelissen, H., Zanne, A., Wirth, C., Coomes, D.A. (2008). Global meta-analysis of wood decomposition rates: a role for trait variation among tree species? Ecology Letters 12, 45-56.  DOI link
  4. Coomes, D.A. & Grubb, P.J. (1998) A comparison of 12 tree species of Amazonian caatinga using growth rates in gaps and understorey, and allometric relationships. Functional Ecology, 12, 426-435.  click

Roots

  1. Holdaway, R. J., Richardson, S. J., Dickie, I. A., Peltzer, D.A., & Coomes, D.A. (2011). Species- and community-level patterns in fine root traits along a 120000-year soil chronosequence in temperate rain forest. Journal of Ecology, 99(4), 954-963.1466. DOI link

Trait databases

Our group has made its trait datasets available to others:

  1. Kattge, J., Díaz, S., Lavorel, S., Prentice, I. C., Leadley, P., Bönisch, G.,…Coomes, D.A.… Wirth, C. (2011). TRY - a global database of plant traits. Global Change Biology, 17, 2905-2935.
  2. Global Wood Density Database Dryad link