The Comparative - Phylogenetic Method of Reconstructing Evolutionary History
Ackerly, David D. .
Ecological diversity of angiosperms: why do major clades differ?
THE development of large-scale trait databases, combined with advances in seed plant phylogenetics, have opened new windows on the evolutionary history of plant ecological attributes. Many of these traits, such as seed size and wood density, are inherently quantitative and require appropriate evolutionary models for ancestral reconstruction and other historical inferences. One of the persistent and surprising results of these analyses is the observation of small but significant differences in mean trait values among major clades, relative to all angiosperms. For example, the eurosids and Ericales have large seeds, while the euasterids have small seeds. The Myrtales and Ericales have low leaf nitrogen concentrations and/or specific leaf area (thick or dense leaves), while euasterids and eurosid 1 have high values for both traits. Woodiness occurs at high frequency in magnoliids, rosids, and Ericales, and at low frequency in monocots and euasterids. In this talk I will explore three hypotheses for these patterns: 1) they reflect contingent historical patterns: small divergences early in angiosperm diversification persist to the present, as predicted based on Markovian processes such as Brownian Motion; 2) trait evolution reflects underlying historical biogeography and limitations on dispersal, causing major clades to predominantly occupy different geographic regions, and hence different adaptive environments; 3) these and other ecological traits predispose lineages to occupy certain environments, leading to stabilizing selection and maintenance of ecological differences among major groups. The latter two processes are difficult to disentangle, but fundamentally differ in their emphasis on dispersal limitation vs. ecological sorting processes, respectively. Several lines of evidence support the third hypothesis, suggesting that sorting processes and stabilizing selection may exert subtle but persistent influences on trait evolution at very large spatial and temporal scales.
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1 - University of California, Berkeley, Department of Integrative Biology, 3060 Valley Life Sciences Bldg #3140, Berkeley, California, 94720, USA
Presentation Type: Symposium or Colloquium Presentation
Location: 314/Bell Memorial Union
Date: Wednesday, August 2nd, 2006
Time: 4:00 PM