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Long-term tropical lizard decline
linked to El Niño events
STRI Panama

Natural ups and downs in the numbers of a tropical lizard species may be a result of global-scale El Niño events, according to a unique 40-year census conducted at the Smithsonian Tropical Research Institute in Panama.

The estimated number of lizards on Barro Colorado Island has declined dramatically: In the last decade, census takers recorded only about 35 percent of the number of lizards, Anolis apletophallus, present during 1970-1980.

“Lizard populations fluctuate wildly from year to year,” said Jessica Stapley, who analyzed data taken between 1970 and 2010. “Only with a study stretching over decades is it possible to see such a dramatic decline,” continued the former post-doctoral fellow at the Smithsonian, now a research fellow at the University of Sheffield, UK.

Stapley found that lizard population growth rate increased following cooler, wetter, La Niña years and decreased following warmer, drier, El Niño years. Several of the major crashes in lizard numbers followed severe El Niño years.

“The fact that the frequency and severity of El Niño and other climate fluctuations seems to be increasing is worrisome,” Stapley said. Increases in the minimum nighttime temperature and in the severity of rainfall events also occurred on Barro Colorado Island during the study period.

“This is the kind of research that STRI is uniquely capable of supporting,” said STRI staff scientist and emeritus director, Ira Rubinoff. “Without these kinds of data, much climate change inference is little more than speculation.”

For many years, Rubinoff has used the Anolis data from Barro Colorado Island as an example of the need for long term studies that make it possible to see what is happening in the big picture, not just during a given year or season.

“This kind of data puts natural fluctuations in a population’s abundance in context, moderating the inevitable call for drastic interventions when one species or another was discovered to have materially increased or decreased,” Rubinoff said, “We would be well served by more studies such as this.”

Former staff scientist A. Stanley Rand began the census. Robin Andrews, now professor at Virginia Tech, expanded the census during the 1980’s to include other sites as part of her doctoral thesis research. Milton Garcia, research manager at the Smithsonian in Panama, continued to follow her methods in succeeding years.

The Smithsonian’s history of 100 years of science in Panama continues to make it possible to answer questions about how intricate tropical forest and reef ecosystems respond to environmental change.

Citation: Stapley J, Garcia M, Andrews RM (2015) Long-Term Data Reveal a Population Decline of the Tropical Lizard Anolis apletophallus, and a Negative Affect of El Nino Years on Population Growth Rate. PLoS ONE 10(2): e0115450. doi:10.1371/journal. pone.011545.

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