Friday, August 11, 8:00-11:30 am
Symposium 23 - Species invasion and species saturation: reconciling patterns of change in biodiversity
Ballroom B, Ballroom Level, Cook Convention Center
Organized by: TJ Stohlgren (tom_stohlgren@usgs.gov), S Simonson, D Sax, and D Tilman

This symposium will hopefully improve our understanding of species saturation in structuring ecological systems in light of invasions and many basic issues in ecology: alternate stable states, regional and global homogenization, and invasion meltdown, to name a few.

The coexistence paradox: why do native and invading competitors coexist despite separate evolutionary histories?

Tilman, David *,1, 1 University of Minnesota, St. Paul, MN

ABSTRACT- A broad range of observational, paleontological and experimental studies show that coexistence, rather than competitive displacement, is and long has been the observed norm for life on earth. This observation raises a number of questions: Why havenít three billion of years of natural selection led to the evolution of a few highly superior species that competitively displace all others? Why has local diversity increased in tandem with global diversity? Why, in many cases, did even species with distinct phylogenetic histories and that evolved in different biogeographic realms coexist after immigration into new realms? A review of a variety of evidence suggests such patterns cannot be explained by Hubbellís Neutral Theory of Biodiversity. However, the evidence provides strong support for the role of evolutionarily unavoidable interspecific tradeoffs as the cause of almost universal coexistence of competing species.

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