|Alexander von Humboldt award lecture
DAVID TILMAN – University of Minnesota and University of California, Santa Barbara, USA
Biodiversity: From Evolutionary Origins to Ecosystem Functioning
Numerous lines of evidence support a “Universal Tradeoff Hypothesis,” which posits that the same interspecific tradeoffs that lead to speciation also lead to multi-species coexistence, and cause ecosystem functioning to be strongly dependent on biodiversity. For instance, fossil records for mollusks, mammals, trees, and other taxa show that, with rare exception, ecologically similar species have coexisted for a million years or more after interchange between formerly isolated realms. Because competition theory predicts that multispecies coexistence requires that species have traits that fall on the same interspecific trade-off surface, the observed coexistence after interchange suggests that during their speciation and subsequent evolution, all species have consistently been bound to the same interspecific trade-off surface despite different phylogenetic and geographic origins. Moreover, theories of multi-species competition also predict that higher diversity leads to greater ecosystem productivity and greater stability if the competing species can coexist because of interspecific tradeoffs.
The Universal Tradeoff Hypothesis thus has the potential to provide a single unifying explanation for the evolutionary origins of biodiversity, for mechanisms of multi-species coexistence, and for ecosystem processes. In so doing, it strengthens the logical basis for the assertion that the loss of biodiversity, whether from species extinctions, community simplification, or loss of genetic variation within populations, can have serious implications for global environmental sustainability.
|Honorary membership lecture
BASTOW WILSON – University of Otago, New Zealand
The four theories in vegetation science
Theories have never fared well in vegetation science. The Clements/Gleason theory (for their theories were almost identical) is the basis of three major ecological concepts: (1) Environmental filtering: its operation is, as Warming said, trivial, though it has always been documented and continues to be, with a few brave attempts to find deeper meanings. (2) Switches: they seem likely to be pervasive in natural communities, but evidence for them is sparse. (3) Assembly rules (present in Clements/Gleason theory only as a single aside by Clements): these are essentially micro-scale switches; evidence for them is easy to obtain, but valid evidence much less easy. The elephant in the room is C-S-R theory, testable but hardly tested.