Biodiversity threatened in rainforest

March 23, 2006, vol. 35, no. 6
By Jennifer Gardy

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What would you do if a former student called you in a panic to report that his field experiment had just burned to the ground?

If you're Arne Mooers, an assistant professor in the department of biological sciences, you take that disaster and turn it into an important discovery with implications for the future of tropical forests.

In 1998, Danny Cleary - who as a PhD student at the University of Amsterdam was being co-supervised by Mooers - returned to Borneo to continue his field studies investigating how logging in tropical forests affected biodiversity.

Instead of finding logged plots of land, however, Cleary was confronted with a charred landscape. A series of El Niño-associated fires in 1997 and 1998 had destroyed more than five million hectares of tropical forest. "El Niño causes severe drought conditions in places like Borneo. As we know from recent history in the interior of B.C., drought can turn little fires into catastrophes," explains Mooers.

An upset Cleary, who had spent months setting up his experiment in harsh jungle conditions, emailed his committee for advice. "We told him this was actually an opportunity of a lifetime to document what happened after such a big fire," says Mooers. "I helped convince him to start collecting data immediately."

Between 1998 and 2004, Cleary sampled the butterfly population in the ruined forest several times. "He collected an amazing number of butterflies," Mooers says. "Over 30,000 individuals from over 520 species." The butterflies were originally classified by species to measure species richness, and then more recently by genotype to measure genetic diversity.

"We can isolate DNA - even from a single butterfly leg - from many individuals of the same species," explains Mooers. "If we compare the same short stretches of DNA between the individuals, we can ask how variable the population is: a large, genetically healthy population will have lots of differences among individuals - think humans in Vancouver - whereas a population that is very small or inbred will show few differences - think humans in some remote mountain village 100 years ago."

When the team of researchers, which had now expanded to include French and British scientists, began to analyse the species' richness and genetic diversity data, a frightening picture emerged.

"We had already reported that the fires and drought in Borneo had caused hundreds of butterfly species to disappear," Mooers notes. "What we discovered here was that the genetic health of the species robust enough to survive was strongly affected in parallel - where we lost more species, we lost more genetic variation within species. This suggests that the species that remain after a catastrophe may be less well-equipped genetically for the future. El Niño-associated events seem to be getting worse and more frequent, so this is a real worry."

A small ray of hope did emerge from the team's study, however. "As a species' numbers slowly recovered, so did the genetic health of the species which had struggled through," explains Mooers.

"Because of this parallel loss and recovery of species richness and within-species variation, if we focus on preserving the first, we may get the surprising benefit of preserving the second."

The team reported their latest findings in the March 2006 issue of the journal Ecology Letters in one installment in a series of papers examining the effects of El Niño on tropical biodiversity. And what lies in the future of this globally important ecosystem?

"Biodiversity in tropical rainforests is being decimated, there is no question. Our experience in Borneo suggests that a perfect storm may be gathering. Climate change is going to affect everything," says Mooers. "The speed at which the earth is changing really is frightening."

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