Photograph courtesy Thomas Martin, Jean-Philippe Sobczak, and Hendrik Dietz, T.U. Munich

Read Caption

A scarab beetle in the understory of the San Lorenzo forest.

Photograph courtesy Thomas Martin, Jean-Philippe Sobczak, and Hendrik Dietz, T.U. Munich

Vast Diversity of Arthropods in Small Patch of Rain Forest

Insect diversity is linked to diversity in plants, study finds.

Though birds, trees, and orchids call the tropical rain forest home, they are immensely outnumbered by tiny arthropods, such as insects, spiders and millipedes. In the past, scientists had trouble estimating how many arthropods exist in the vastness of a forest. But thanks to new methods of sampling and analysis, researchers now think that over 25,000 different species of arthropods live in just one forest.

These findings are part of Project IBISCA-Panama, an extensive survey of arthropods in Panama's San Lorenzo forest supported by the Smithsonian Tropical Research Institute. The study, published in this week's issue of Science, revealed that an estimated 25,000 species of arthropods exist in the 6,000-hectare forest. By tallying these small organisms, researchers hope to get a better grasp of their many roles in the rain forest ecosystem.

"Arthropods are important in all the functions of the forest: pollination, early decomposition, [consumption] of leaves in the forest, [providing] nutrients in soil, and regeneration of [the] forest," says Yves Basset, scientific coordinator of the Institute's CFTS Arthropod Initiative and lead author of the study.

Since many arthropod species face extinction, Basset says that conservation efforts can be focused if we know how many species exist and which of those species are functionally redundant. "If we have a thousand species breaking up wood in the forest, we want to know if we could maybe simplify this with maybe 500 species ... Can we afford to lose them? Is the basic function of the forest affected?"

The researchers discovered that the areas of the forest with the most arthropod diversity also had the greatest diversity of plants. "It means if we want to save areas of high species richness, we may [want to] focus on sites with plant species [richness]," Tomas Roslin, co-author of the study and professor at the University of Helsinki, Finland, said in a press conference on Wednesday.

The scientists combed the forest floor, then used new methods, such as a construction crane and hot air balloons, to reach the canopy. Basset and his team sampled from a dozen sites in the forest, collecting 130,000 individuals that were then classified into 6,100 distinct species. (Related pictures: Miniature Ecosystems.)

Using these data—almost a decade in the making—the researchers could then apply mathematical formulas to extrapolate the estimated 25,000 arthropods in the entire forest.  Based on these calculations, researchers also discovered that nearly two-thirds of these species are represented in just one hectare of the forest. This means that in the future, scientists can accurately study the diversity of a forest the size of Manhattan by only studying an area equivalent to a few city blocks.

Executing an experiment of this magnitude required a collaboration of over a hundred researchers from 21 different countries, Basset says. "You need to be an expert in ants to identify them, and you need to be a butterfly expert to do the same. The diversity of the experts working on the project is just a reflection of the diversity of the arthropods themselves," he says.

This large-scale interdisciplinary effort marks a first in the field of tropical entomology, says Basset. "In the past we've had quite a few [similar projects] but only targeting a single group, like ants or butterflies. This is the first project where we're trying to sample representative of each group of arthropods," he says.

Though the scientists are heartened by the richness of the tropical arthropod world they discovered, conservation efforts are still very important, Basset says.

"I would be quick to point out that if we have so many species in half a hectare, that doesn't mean that they are able to subsist in only half a hectare. We can collect them because they pass through, but that doesn't mean that you could cut the forest to just one or two hectares and preserve the biodiversity [of the whole forest]," he says.