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.
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:
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.
Leaves and leaf litter
Stems and deadwood
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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
Roots
Trait databases
Our group has made its trait datasets available to others:
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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