Don't it always seem to go
That you don't know what you've got
Till it's gone.
They paved paradise
And put up a parking lot.
-Joni Mitchell, "Big Yellow Taxi"
Going, going, gone.
Since 1960, population biologist Paul Ehrlich and his research group have been conducting a classic study of the population of Jasper Ridge's Bay checkerspot butterflies, subspecies Euphydryas editha bayensis. But now the biologists won't have to muck about the ridge counting insects as they have for decades to characterize rates of births, deaths, immigrations and emigrations. The last two Jasper Ridge populations went extinct in 1991 and 1998. Examining 70 years of rainfall and population data, the researchers now conclude that extreme swings in regional climate hastened extinction of the butterflies. They report their findings in the April 30 issue of the Proceedings of the National Academy of Sciences.
"This is the first time anyone has documented the effects of weather variation linked to climate change on extinction of populations," says Ehrlich, the Bing Professor of Population Studies. Previous studies have looked at shifts in average conditions - say, the climate becomes drier or wetter overall - or the effects of a single extreme climate event, such as a hard freeze. The Stanford study instead examined the effect of climate variability - swings in rainfall highs and lows - on extinction, and tied the extinctions tightly to a mechanism. "People have long been aware of the problem of species extinctions, but are just beginning to realize the importance of population extinctions."
Not only are population extinctions a prelude to species extinctions, but they also threaten the vital ecosystem services upon which human life depends. Stanford's Center for Conservation Biology has pioneered investigations of population extinctions, in part because of the Ehrlich group's observations on the extirpation of checker
Contact: Dawn Levy