"We already knew," Smith says, "that at each site we were losing roughly half the species. Our analysis confirmed this. Before the fungus, an average 45 species were observed at each site; after the fungus, the average was only 23.
But the beta diversity dropped even more precipitously than the alpha diversity because the fungus preferentially attacked endemic species found only at one or a few sites. Among the species in the study, 42 percent were found at only one site; a disproportionate share of these species disappeared.
The loss of rare species drove regional extinctions higher than expected. "Our simulations showed that random local extinctions would have resulted in 41 regional extinctions across the eight sites," Smith says, "but instead we observed 61 regional extinctions."
Regional extinction may mean global extinction.
"The regional extinctions strongly suggest these species are gone not just from the region but from the planet," says Smith. "It's very difficult to document an extinction, because you have to prove a negative. But if you see that a species is gone not only from point A but also from points B, C and D that gives you a much stronger case."
In homogenizing the frog communities, the fungus erased chapters in evolutionary history. Two rare families of frogs, the Aromobatidae and the Hemiphractidae, disappeared from the region.
Among the Hemiphractidae, also known as the marsupial frogs, males capture eggs as the female lays them and deposit them in pouches on the female's back. The female then totes the eggs around with her until they hatch.
Homogenization also knocked out ecological diversity. Before the invasion there was a good mix of species in the region. Some species lived in streams, others on land, in trees and underground.
|Contact: Kevin Smith|
Washington University in St. Louis