Lancaster and Kay are the first to tackle the question using modern methods of phylogenetic analysis. They studied 16 different plant lineages that are well represented both within and outside of California, and each lineage includes California endemic species. Using DNA sequence data to reconstruct the evolutionary "family trees" of these lineages, plus fossil records to calibrate the dates when different branches of each tree diverged, they were able to estimate historical rates of speciation, extinction, and migration across the California border.
Some of the study's key findings differ from long-standing ideas about the origins of California's extraordinary species richness that were set forth in a landmark study published in 1978, "Origin and relationships of the California flora," by Peter Raven and Daniel Axelrod. That classic work, which was based on analyses of fossil data and current distributions of plants, emphasized high speciation rates as an important contributor to high plant biodiversity in California.
Raven and Axelrod also hypothesized that the onset of the wet-winter, dry-summer Mediterranean climate in California 3 to 5 million years ago was a key factor that promoted high rates of speciation and led to the species richness that now characterizes California's flora. All the regions of the world with a Mediterranean climate (California, the cape of Africa, Southwestern Australia, the west coast of Chile, and around the Mediterranean sea) are currently plant biodiversity hotspots, and California does have a large number of relatively young species.
Lancaster and Kay's study, however, indicates that the onset of the Mediterranean climate did not affect speciation rates in California i
|Contact: Tim Stephens|
University of California - Santa Cruz