According to Kay, California's topographical diversity probably has played a critical role in preserving species richness. "People have talked about the topography fostering speciation, and it does play a role in that, but it plays a bigger role in preventing extinction by creating different niches and allowing lots of species to coexist," Kay said. "Topography also provides refuges, and the mountains are particularly important in preventing extinctions during times of climate change."
In a changing climate, species living on mountains can stay in the same temperature regime by shifting their elevation, moving relatively short distances compared to species on flat land that would have to shift their latitude by hundreds of miles to stay in the same temperature range. California's mountains are also important for their influence on precipitation, capturing the moisture in air masses coming off the Pacific Ocean, Kay said.
The new study did support several of Raven and Axelrod's conclusions. For example, they had predicted that cold-adapted lineages would have lower rates of speciation in California than warm-adapted lineages, which Lancaster and Kay confirmed. They also proposed that the onset of the Mediterranean climate facilitated the immigration of desert-adapted plants. Lancaster and Kay found that desert-adapted plants colonized California more recently than other lineages, arriving on average around 5 to 6 million years ago, in comparison to an average of around 17 million years ago for non-desert lineages.
"We just don't have a lot of evidence that the Mediter
|Contact: Tim Stephens|
University of California - Santa Cruz