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Invasion of exotic species...

Data recently published in the journal Science a few issues ago give the number of exotic species found in San Francisco Bay through time, since 1850. We've collected a lot of new biotic material in a relatively short period of time. The authors calculate that between 1961 to 1995, we're adding one new species every fourteen weeks. We're not talking thousands, hundreds of thousands, millions of years, we're talking weeks. This is the rate of change that we're seeing today, a very different kind of change than what's just been talked about in the earlier presentations.

The San Francisco Bay is one place close to us, a place dear to us, and it is probably one of the most disrupted estuaries in the world. Looking more broadly, at the United States as a whole, we can see an extraordinary increase in species additions. Now we're talking thousands of new species entering into the biota and influencing the interactions that we just heard about, new biotic interactions and new evolutionary sub-pathways are being opened up.

If we look at the increase in invading arthropods through time in the US, we see a rapid increase, then a slight leveling off, and then again a continued rapid increase. The slight decrease in the slope of the curve relates to when the quarantine system was established. An enormous amount of money and effort has been put into the quarantine service, and probably rightly so. The quarantine system is, however, certainly not a very fine filter. California saw an increase in plant invasions, even after the quarantine system began. We're now at a thousand new species -- a tremendous number of new additions to the biota.


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