November 30 2017

5:00 pm 1100 TLSB

EcoEvoPub Series

Graduate Student Presentations


Department of Ecology and Evolutionary Biology, UCLA

“The Several Ways to Build a Tree: a Look into the Diversity of Growth Strategies in an Amazon Forest”

Adult height is a fundamental trait in plant ecology as it reflects the vertical partitioning of light in forests, and yet we are far from understanding how this trait evolves. Evolution of adult height seems to be complex, with several lineages converging to become canopy trees, some lineages converting back into understory dwellers, while whole clades have conserved their short statures. Such patterns are compatible with the idea that some intrinsic factors are limiting the evolutionary increase in height in certain lineages, but what could be those constraints? It has been hypothesized that canopy trees, while saplings in the understory, tend to invest in vertical growth at the expenses of lateral crown expansion, which is prefered by most understory treelets. These contrasting growth strategies, however, are likely determined by crown architecture, which in turn depends on other phylogenetic conserved traits such as phyllotaxy and blade division. My purpose is to test these hypotheses using a set of > 1000 tree species found in a forest in Central Amazon, which encompasses most of the diversity in growth strategies and architectures found among plants.


Department of Geological Sciences, Stanford

“Competition for Epidermal Space in the Evolution of Leaves with High Physiological Rates”

Leaves with high photosynthetic capacity also have high transpiration capacities, so that hydraulic conductance, stomatal conductance, and assimilation capacities should all be positively correlated. This is potentially problematic since these traits all make independent demands on anatomical space, particularly due to the propensity for veins to have bundle sheath extensions that are expressed on the epidermis as fields of cells where stomata are excluded. We measured the density and area occupation of bundle sheath extensions, the density and size of stomata and their subsidiary cells, and venation density for a sample of extant canopy-reaching angiosperms. These measurements were complemented with similar measurements in both fossil and living vascular plants with laminate, multi-veined leaves. Conflicts and tradeoffs for occupation of epidermal space are indeed found to be important, even for low vein density plants. Whether vein density is high or low, even modest increases in vein density with the concomitant increases in stomatal conductance would require substantial reconfigurations of anatomy. This likely contributes to the stability in leaf characteristics—and ecophysiology—seen through time in different lineages and contributes to the uniqueness of angiosperms in achieving the highest vein densities, stomatal densities, and physiological rates. In particular, flowering plants are distinguished by their capacity for small cell sizes and for hierarchical vein networks that allow expression of bundle sheath extensions in some, but not all of their veins, as opposed to the all-or-nothing alternatives required with the non-hierarchical vein networks seen in most non-angiosperms.











































































































































































































































































































































































































































































































































































































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