Still, she tried to find out. She and her team, including snake expert Julie Ray of Panama’s La MICA Biological Station, conducted more than 1,000 surveys of the El Copé region. They began in 1997, anticipating Bd’s onslaught, and for 13 years found, identified, and counted every reptile and amphibian they could. Before the epidemic, the team saw 30 snake species. Afterward, they saw just 21.
That seems like clear-cut evidence of a decline, but it’s not. Some of the snakes are so rare that during the team’s years of work, they saw 12 of the species just once. And they only saw a few of these after Bd had passed through. It’s not as if those snakes had suddenly migrated into the area; they were probably there before, and just hadn’t been spotted. But if that’s the case, how could the team possibly know if any of the trends in their data were real? If a snake was found in the pre-Bd era but not the post-Bd years, was it actually missing, or did the team just miss it?
“I don’t think I appreciated how difficult it was going to be,” Lips says. “It took a long time to find someone to help us analyze the data.”
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That person was Elise Zipkin. A number-crunching ecologist at Michigan State University, Zipkin specializes in estimating how animals react to changing environments, especially when the underlying data are imperfect. (“My job is making lemonade out of lemons,” she told me.) Working with Lips, she built a mathematical model that represents the snake community in El Copé. The model assumes that different species will vary in abundance—some extremely common, some extremely rare, and many in the middle. It then predicts how likely these species are to be in a given stretch of forest at any one time, and how likely a herpetologist walking through that stretch is to actually spot them. By looking at the model’s predictions and working backwards, Zipkin could use the number of snakes that Lips saw to estimate how many snakes there actually were at the time.
Zipkin calculated that there’s an 85 percent chance that the number of snake species went down after Bd slaughtered El Copé’s frogs, and a 99 percent chance that the community became more homogenous—that is, what’s left is much the same everywhere. “That’s horrible,” says Patricia Burrowes, a herpetologist at the University of Puerto Rico. “When we homogenize a place like El Copé that’s so diverse, you end up losing amazing species—and those that are the rarest go first.”
There are other worrying signs. Of the more commonly observed species, Zipkin estimated that around half declined in number after the epidemic, a quarter increased, and a quarter were unaffected. For the six species that were seen most often, four were smaller after the epidemic, and two were bigger. “Some things do better, but most things do badly, and everything looks more similar on a regional scale,” Zipkin says. The same trends befall most ecosystems under stress.